Dissertations / Theses: 'Multilevel Power Converters'

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Ferreira, Abel António de Azevedo. "Modular multilevel converters for power system applications." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/405894.

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This thesis discusses the operation of the grid-tied modular multilevel converters (MMC) applied on the dc power transmission, particularly on the medium and high-voltage applications. First, it is presented the evolution of the power converters used on the high-voltage dc transmission field (HVdc) with special focus on the modular multilevel-based power converters. Then, due to the intrinsic nature of the converter, besides the control requirements for its dc and ac buses interactions, its energy storage should be carefully managed in order to achieve a safe and knowledgeable operation of this power converter. Hence, its control requirements are presented and mathematically supported. Moreover, the progressive design and validation of its control loops is addressed in this thesis by means of the converter simulation over a broad range of operating conditions. One key-point factor of the MMC performance is the strategy followed to modulate the voltages generated on its arms. In this vision, different modulation techniques were combined with peculiar zero sequence signals in order to analyze their impact on the voltages across the converter arms and its intrinsic performance. This study was also complemented by different procedures followed to balance the energy storage of its capacitors. A transversal research question of this voltage source converter topology is its efficiency. Then, besides the analysis of the ac power flow impact on the power losses produced by its semiconductors, it is deduced and proposed a mathematical expression that that can describe the power losses produced semiconductors, over a broad range of operating conditions of the MMC. Finally, it is explored the possible degrees of freedom of an half-bridge-based MMC whenever it is operating in the static synchronous compensation (STATCOM) mode. Depending on the converter operation aspect that is required to be optimized, the voltage across its dc poles can be adjusted to achieve an improved performance of the MMC
La presente tesis trata sobre el funcionamiento de los convertidores modulares de multinivel (MMC) utilizados en la transmisión de energía eléctrica en corriente continua, en particular para aplicaciones de media y alta tensión. En primer lugar, se presenta la evolución de los convertidores utilizados en el campo de la transmisión de energía eléctrica mediante enlaces en corriente continua de alta tensión(HVdc), haciendo especial énfasis en los convertidores de topología multinivel. Debido a la naturaleza intrínseca del convertidor MMC, se debe regular el intercambio de potencia entre las redes de corriente alterna y continua a las que se conecta, junto con la energía interna almacenada, para asegurar un buen funcionamiento del mismo. Por ello, se presenta una descripción del control del convertidor soportada por un riguroso análisis matemático. El diseño de los diferentes lazos de control se valida mediante simulaciones representando diferentes condiciones de funcionamiento posibles. Un factor clave del rendimiento del MMC es la estrategia de modulación utilizada para aplicar voltajes en cada una de sus ramas. Para evaluar sus diferencias a nivel de pérdidas, se presenta una comparativa entre diferentes técnicas de modulación incorporando secuencia homopolar. Este estudio se complementa con el estudio de diferentes procedimientos seguidos para equilibrar el almacenamiento de energía en los condensadores de una rama. Una cuestión de investigación transversal de esta topología de convertidor de tensión es su eficiencia. Posteriormente, se obtiene una expresión matemática que permite describir las pérdidas de los semiconductores del convertidor en funcionamiento, para diferentes niveles de transferencia de potencia. Finalmente, se analizan los posibles grados de libertad de un MMC operando en modo de compensación de potencia reactiva (STATCOM). En base a la operación de dicho convertidor y de la variable que se requiera optimizar, resulta posible variar la tensión entre sus polos DC para lograr un mejor funcionamiento del convertidor

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Serbia, Nicola. "Modular Multilevel Converters for HVDC power stations." Phd thesis, Institut National Polytechnique de Toulouse - INPT, 2014. http://tel.archives-ouvertes.fr/tel-00945375.

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Les travaux présentés dans ce mémoire ont été réalisés dans le cadre d'une collaboration entre le LAboratoire PLAsma et Conversion d'Énergie (LAPLACE), Université de Toulouse, et la Seconde Université de Naples (SUN). Ce travail a reçu le soutien de la société Rongxin Power Electronics (Chine) et traite de l'utilisation des convertisseurs multi-niveaux pour le transport d'énergie électrique en courant continu Haute Tension (HVDC). Depuis plus d'un siècle, la génération, la transmission, la distribution et l'utilisation de l'énergie électrique sont principalement basées sur des systèmes alternatifs. Les systèmes HVDC ont été envisagés pour des raisons techniques et économiques dès les années 60. Aujourd'hui il est unanimement reconnu que ces systèmes de transport d'électricité sont plus appropriés pour les lignes aériennes au-delà de 800 km de long. Cette distance limite de rentabilité diminue à 50 km pour les liaisons enterrées ou sous-marines. Les liaisons HVDC constituent un élément clé du développement de l'énergie électrique verte pour le XXIème siècle. En raison des limitations en courant des semi-conducteurs et des câbles électriques, les applications à forte puissance nécessitent l'utilisation de convertisseurs haute tension (jusqu'à 500 kV). Grâce au développement de composants semi-conducteurs haute tension et aux architectures multicellulaires, il est désormais possible de réaliser des convertisseurs AC/DC d'une puissance allant jusqu'au GW. Les convertisseurs multi-niveaux permettent de travailler en haute tension tout en délivrant une tension quasi-sinusoïdale. Les topologies multi-niveaux classiques de type NPC ou " Flying Capacitor " ont été introduites dans les années 1990 et sont aujourd'hui couramment utilisées dans les applications de moyenne puissance comme les systèmes de traction. Dans le domaine des convertisseurs AC/DC haute tension, la topologie MMC (Modular Multilevel Converter), proposée par le professeur R. Marquardt (Université de Munich, Allemagne) il y a dix ans, semble particulièrement intéressante pour les liaisons HVDC. Sur le principe d'une architecture de type MMC, le travail de cette thèse propose différentes topologies de blocs élémentaires permettant de rendre le convertisseur AC/DC haute tension plus flexible du point de vue des réversibilités en courant et en tension. Ce document est organisé de la manière suivante. Les systèmes HVDC actuellement utilisés sont tout d'abord présentés. Les configurations conventionnelles des convertisseurs de type onduleur de tension (VSCs) ou de type onduleur de courant (CSCs) sont introduites et les topologies pour les systèmes VSC sont ensuite plus particulièrement analysées. Le principe de fonctionnement de la topologie MMC est ensuite présenté et le dimensionnement des éléments réactifs est développé en considérant une commande en boucle ouverte puis une commande en boucle fermée. Plusieurs topologies de cellules élémentaires sont proposées afin d'offrir différentes possibilités de réversibilité du courant ou de la tension du côté continu. Afin de comparer ces structures, une approche analytique de l'estimation des pertes est développée. Elle permet de réaliser un calcul rapide et direct du rendement du système. Une étude de cas est réalisée en considérant la connexion HVDC d'une plateforme éolienne off-shore. La puissance nominale du système étudié est de 100 MW avec une tension de bus continu égale à 160 kV. Les différentes topologies MMC sont évaluées en utilisant des IGBT ou des IGCT en boitier pressé. Les simulations réalisées valident l'approche analytique faite précédemment et permettent également d'analyser les modes de défaillance. L'étude est menée dans le cas d'une commande MLI classique avec entrelacement des porteuses. Enfin, un prototype triphasé de 10kW est mis en place afin de valider les résultats obtenus par simulation. Le système expérimental comporte 18 cellules de commutations et utilise une plate-forme DSP-FPGA pour l'implantation des algorithmes de commande.

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Lund, Richard. "Multilevel Power Electronic Converters for Electrical motor Drives." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-687.

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Power electronic converters are widely used in industrial power conversion systems both for utility and drives applications. As the power level increases, the voltage level is increased accordingly to obtain satisfactory efficiency. During the last years, the voltage rating of fast switching high voltage semiconductors such as the Insulated Gate Bipolar Transistor (IGBT) has increased. Still, there is a need for series connection of switching devices. In this area of applications, the Multilevel Converter has shown growing popularity.

The fundamental advantages of the Multilevel Converter topologies are low distorted output waveforms and limited voltage stress on the switching devices. The main disadvantages are higher complexity and more difficult control.

In this thesis, Multilevel Converters are analysed for large motor drive applications. The main focus has been on converter losses, output waveform quality and control.

Analytical expressions for both switching and conduction losses for 4- and 5-level Diode Clamped Converters have been developed. The investigation shows that the losses can be reduced by utilizing a multilevel topology for a 1 MW drive. This work is presented in [46]. The same reduction in losses is proven for a 2300V/ 3 MW drive.

Analytical expressions for the harmonic losses in 3-level converters have been developed for 2 different Carrier Based PWM schemes, presented in [56], [57] and [58]. Also Space Vector PWM are investigated and compared by simulations, in addition to 4- and 5-level Carrier Based PWM.

DC-bus balancing in both 3- and 5-level converters is discussed. Balancing in 3- level converters can be achieved by proper control. Balancing in 5-level converters can be achieved by proper arrangement of isolated DC-supplies.

One 40kW 3-level converter and one 5kW 5-level converter has been designed and built. Experimental verification of the analytical and simulated results is shown.

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Peftitsis, Dimosthenis, Georg Tolstoy, Antonios Antonopoulos, Jacek Rabkowski, Jang-Kwon Lim, Mietek Bakowski, Lennart Ängquist, and Hans-Peter Nee. "High-Power Modular Multilevel Converters With SiC JFETs." KTH, Elektrisk energiomvandling, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-52687.

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This paper studies the possibility of building a modular multilevel converter (M2C) using silicon carbide (SiC) switches. The main focus is on a theoretical investigation of the conduction losses of such a converter and a comparison to a corresponding converter with silicon-insulated gate bipolar transistors. Both SiC BJTs and JFETs are considered and compared in order to choose the most suitable technology. One of the submodules of a down-scaled 3 kVA prototype M2C is replaced with a submodule with SiC JFETs without antiparallel diodes. It is shown that the diode-less operation is possible with the JFETs conducting in the negative direction, leaving the possibility to use the body diode during the switching transients. Experimental waveforms for the SiC submodule verify the feasibility during normal steady-state operation. The loss estimation shows that a 300 MW M2C for high-voltage direct current transmission would potentially have an efficiency of approximately 99.8% if equipped with future 3.3 kV 1.2 kA SiC JFETs.
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Hassan, Bakri. "Current fed multilevel converters for high current power applications." Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3267.

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The majority of the worldwide installed power inverters today are voltage source inverters followed by current source inverters where the concluding decision lies with the performance of the applications besides the usual economic reasons. Recent active development in the current source inverter areas has seen the emerging of various generalized multilevel current source inverter topologies analogous to the existing multilevel voltage source inverter families. To date, the multilevel current source inverter families have been classified principally by the physical appearance of their basic structures and also by the number of current sources employed. The existing multilevel current source inverter topologies are unpopular for present applications due to reasons such as big sizes, high control complexity and low reliability; which circumstances are often associated to massive component counts and multiple requirements of current sources. Therefore, this research has been focused on the single-phase single-source generalized multilevel current source inverter for this apparent advantage; where this thesis proposed a novel generalized multilevel current-source inverter topology with the lowest component utilization while employing just a single current source. In addition, the proposed topology can conveniently achieved dc current balance with a simple low frequency switching strategy for the five- and nine-level current outputs. From comparison analysis, the proposed topology has significantly less number of components employed compared to the nearest topology, which implies low implementation cost. The experimental results verify the characteristics and performances of the proposed topology acquired by computer simulations.

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Sternberger, Ronny. "Analytical modelling and controller design of a multilevel STATCOM." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25797.

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Elamalayil, Soman Deepak. "Multilevel Power Converters with Smart Control for Wave Energy Conversion." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-332730.

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The main focus of this thesis is on the power electronic converter system challenges associated with the grid integration of variable-renewable-energy (VRE) sources like wave, marine current, tidal, wind, solar etc. Wave energy conversion with grid integration is used as the key reference, considering its high energy potential to support the future clean energy requirements and due the availability of a test facility at Uppsala University. The emphasis is on the DC-link power conditioning and grid coupling of direct driven wave energy converters (DDWECs). The DDWEC reflects the random nature of its input energy to its output voltage wave shape. Thereby, it demands for intelligent power conversion techniques to facilitate the grid connection. One option is to improve and adapt an already existing, simple and reliable multilevel power converter technology, using smart control strategies. The proposed WECs to grid interconnection system consists of uncontrolled three-phase rectifiers, three-level boost converter(TLBC) or three-level buck-boost converter (TLBBC) and a three-level neutral point clamped (TLNPC) inverter. A new method for pulse delay control for the active balancing of DC-link capacitor voltages by using TLBC/TLBBC is presented. Duty-ratio and pulse delay control methods are combined for obtaining better voltage regulation at the DC-link and for achieving higher controllability range. The classic voltage balancing problem of the NPC inverter input, is solved efficiently using the above technique. A synchronous current compensator is used for the NPC inverter based grid coupling. Various results from both simulation and hardware testing show that the required power conditioning and power flow control can be obtained from the proposed multilevel multistage converter system. The entire control strategies are implemented in Xilinx Virtex 5 FPGA, inside National Instruments’ CompactRIO system using LabVIEW. A contour based dead-time harmonic analysis method for TLNPC and the possibilities of having various interconnection strategies of WEC-rectifier units to complement the power converter efforts for stabilizing the DC-link, are also presented. An advanced future AC2AC direct power converter system based on Modular multilevel converter (MMC) structure developed at Siemens AG is presented briefly to demonstrate the future trends in this area.

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Almaleki, Masoud. "Sliding mode observation of capacitor voltage in multilevel power converters." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/11846/.

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Smart power supply grids may be required to link future energy production and consumers. Multilevel converters are a building block for smart grids. There are several structures of multilevel converters, for example the Neutral Point Clamped (NPC), the Flying Capacitor Circuit and the Cascaded H-Bridge (CHB) converter. The modular structure of the CHB multilevel converter makes it one of the best options for smart grids. Using modular converter structures reduces production and maintenance costs. Implementation of efficient and fast controllers for multilevel converters requires accurate measurement of the voltages and currents for the system feedback loops. Knowledge of the DC link voltages is necessary to construct voltage control loops. In a typical CHB multilevel converter there are many DC links which means that a lot of voltage transducers maybe required. Voltage transducers at medium voltage are not easy to implement and add to system cost. This thesis presents an efficient way to observe the DC link voltages and hence eliminate the cost associated with voltage transducers. A “Sliding Mode Observer (SMO) using the Equivalent Control Method” has been chosen because of its robustness against system uncertainties. Simulation and practical work has been performed on a three-phase, three-cell multilevel converter to validate the use of this observer.

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Saleh, Kamel Subhi. "Sensorless Control of High Power Induction Motors Using Multilevel Converters." Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523161.

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Jupin, Samuel. "Advanced Control of Multilevel Power Converters for Weak Grid Applications." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0210.

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Avec l’avènement des micros-réseaux incorporant les sources d’énergie renouvelable, un nouveau paradigme apparaît dans la distribution de l’électricité. Ces nouvelles architectures interfacent des consommateurs non contrôlés à des sources d’énergie intermittentes, plaçant de fortes contraintes sur les étapes de conversion, stockage et gestion de l’énergie.Les convertisseurs de puissance s’adaptent avec en particulier le développement des convertisseurs multiniveaux, qui supportent à composants égaux des puissances plus importantes que leurs prédécesseurs et assurent une meilleure qualité de l’énergie, mais dont le contrôle gagne en complexité.Du fait de leur nature hybride, le contrôle des convertisseurs de puissance est traditionnellement scindé en deux parties. D’un côté les objectifs continus liés à la fonction principale d’interfaçage des convertisseurs, de l’autre le pilotage des interrupteurs quantifiés qui le forment, la modulation.Dans ce contexte, les exigences croissantes en rendement, fiabilité, polyvalence et performance imposent un gain conséquent d’intelligence de l’ensemble de l’architecture de contrôle. Pour répondre à ces exigences, nous proposons de traiter à la fois les objectifs liés à la fonction d’interface des convertisseurs et ceux rattachés à leur nature avec un unique contrôleur. Cette décision implique d’incorporer la non-linéarité des convertisseurs de puissance au contrôleur. Une approche de Contrôle à Modèle Prédictif (MPC) a été retenue pour traiter cette non-linéarité ainsi que la diversité d’objectifs de contrôle qui accompagne les convertisseurs.L’algorithme développé combine la théorie des graphes, avec divers algorithmes comme ceux de Dijkstra et A* à un modèle d’état spécialisé pour les systèmes à commutation, formant ainsi un outil puissant et universel capable de manipuler et la nature discrète des interrupteurs de puissance et celle continue de son environnement. L’étude du modèle d’état utilisé pour les convertisseurs de puissance comme systèmes commutants conduit à des résultats concernant la stabilité et la contrôlabilité de ces systèmes.Le contrôleur obtenu est éprouvé en simulation, face à des cas d’applications variés : onduleur isolé ou connecté à un réseau, redresseur et convertisseur bidirectionnel. La même structure de contrôle est confrontée à chacune de ces situations pour trois topologies multi-niveaux : Neutral Point-Clamped, Flying Capacitor et Cascaded H-Bridge. La capacité d’adaptation du contrôleur est regroupée dans deux étapes : la prédiction, qui utilise le modèle du convertisseur, et la fonction de coût, qui traduit le cahier des charges en un problème d’optimisation résolu par l’algorithme. Changer de topologie implique de modifier le modèle, sans impact sur la fonction de coût, tandis que modifier cette fonction suffit à s’adapter aux différentes applications.Les résultats montrent que le contrôleur pilote directement les interrupteurs de puissance en fonction des objectifs. Les performances générales de cette structure unique sont comparables à celles des structures multiples utilisées pour chacun des cas étudiés, à l’exception notable du fonctionnement redresseur, où la rapidité et l’étendue des possibilités sont tout particulièrement intéressants.En conclusion, le contrôleur développé est capable de traiter un grand nombre d’applications, topologies, objectifs et contraintes. Alors que les modifications du cahier des charges ou des conditions de fonctionnement impactent souvent profondément les structures de contrôle linéaire, ces altérations ne modifient pas l’architecture du contrôleur MPC développé. Cela illustre la polyvalence de la solution proposée ainsi que son universalité, démontrée davantage par la capacité à s’adapter à des convertisseurs de puissance différents et sans modifications. Finalement, la complexité de la modulation est toute incluse dans la structure, offrant un gain de simplicité et de flexibilité au design du contrôle
With the progressive rise of the micro-grids incorporating renewable energy sources, a new electricity distribution paradigm is emerging. These new architectures interface uncontrolled consumers with intermittent energy sources, therefore imposing more stress on the conversion, storage and management of the energy.Power converters are adapting accordingly, in particular, with the development of multi-level converters, which allow higher power rates and better power quality than their predecessors with similar components, but whose control is becoming increasingly complex.Due to their hybrid nature, the control of power converters is traditionally split into two parts: on the one side, the continuous objectives related to the main interfacing function of the power converters, and, on the other side, the driving of their quantized power switches, known as the modulation strategy.In this context, the growing demands in efficiency, reliability, versatility and performance require a high level of intelligence of the complete control structure. To meet these requirements, the objectives of this research work are to address both the interfacing objectives and the inner driving of the converter into a single controller. This decision implies incorporating the non-linearity of power converters into the controller, equivalent to suppressing the traditional modulation block. Modulation is the traditional solution to linearize the inner operation of the converters. The Model Predictive Control (MPC) approach was chosen to handle the non-linearity and the diversity of control objectives that accompany power converters.The developed control algorithm combines graph theory, with Dijkstra, A* and other algorithms, with a special state-space model designed for switching systems to form a powerful universal tool capable of simultaneously manipulating the discrete and continuous nature of the converter and its environment. Switched state-space models are studied, leading to interesting results on stability and controllability concerning their application on power converters.The obtained controller is then tested in simulation, with various case studies: grid-connected and standalone inverter, rectifier and bidirectional operation. These situations are studied for three common multi-level topologies: Neutral Point-Clamped, Flying Capacitor and Cascaded H-Bridge. The exact same MPC structure is used for each and every one of the case studies, with adaptations of its internal behavior. This behavior is agglomerated in two functions: the prediction, containing the model of the converter, and the cost function, which translates the control requirements into the optimal problem solved by the algorithm. Changing the topology implies adjusting the model, without impacting the cost function, while modifying this function is sufficient to adapt to the different applications.The results show that the controller manages to directly drive the power switches according to the application, demonstrating a large variety of considerations and objectives. The overall performance of this unique structure is comparable to that of the multiple structures used for each of the studied cases, with the notable exception of rectifier operation mode, where the speed and range of possibilities are particularly interesting.In conclusion, the developed controller manages miscellaneous applications, topologies, objectives and constraints. While the traditional linear control structures have to change, often deeply, for different operation modes and control requirements, such modifications do not affect the control architecture of the designed MPC controller. This shows the versatility of the proposed solution and its universality, further demonstrated by its ability to adapt to different power converters without modifications. Finally, the complexity of the modulation is fully included in the structure, offering simplicity and flexibility to the control design

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Li, Chen. "State Space Modeling and Power Flow Analysis of Modular Multilevel Converters." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71811.

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For the future of sustainable energy, renewable energy will need to significantly penetrate existing utility grids. While various renewable energy sources are networked with high-voltage DC grids, integration between these high-voltage DC grids and the existing AC grids is a significant technical challenge. Among the limited choices available, the modular multi-level converter (MMC) is the most prominent interface converter used between the DC and AC grids. This subject has been widely pursued in recent years. One of the important design challenges when using an MMC is to reduce the capacitor size associated with each module. Currently, a rather large capacitor bank is required to store a certain amount of line-frequency related circulating energy. Several control strategies have been introduced to reduce the capacitor voltage ripples by injecting certain harmonic current. Most of these strategies were developed using trial and error and there is a lack of a systematic means to address this issue. Most recently, Yadong Lyu has proposed to control the modulation index in order to reduce capacitor ripples. The total elimination of the unwanted circulating power associated with both the fundamental line frequency and the second-order harmonic was demonstrated, and this resulted in a dramatic reduction in capacitor size. To gain a better understanding of the intricate operation of the MMC, this thesis proposes a state-space analysis technique in the present paper. Combining the power flow analysis with the state trajectory portrayed on a set of two-dimensional state plans, it clearly delineates the desired power transfer from the unwanted circulating energy, thus leading to an ultimate reduction in the circulation energy and therefore the required capacitor volume.
Master of Science

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Sernia, Paul C. "Modelling and analysis of random phase and frequency in multilevel, multi-module power converters /." [St. Lucia, Qld.], 2006. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe19367.pdf.

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Yazdani, Atousa. "Energy and voltage management methods for multilevel converters for bulk power system power quality improvement." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Yazdani_09007dcc805c8ecd.pdf.

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Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed February 18, 2009) Includes bibliographical references.

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Tarisciotti, Luca. "Model predictive control for advanced multilevel power converters in smart-grid applications." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27742/.

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In the coming decades, electrical energy networks will gradually change from a traditional passive network into an active bidirectional one using concepts such as these associated with the smart grid. Power electronics will play an important role in these changes. The inherent ability to control power flow and respond to highly dynamic network will be vital. Modular power electronics structures which can be reconfigured for a variety of applications promote economies of scale and technical advantages such as redundancy. The control of the energy flow through these converters has been much researched over the last 20 years. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a Cascaded H-Bridge converter, configured to function as a solid state substation. The work considers the derivation and application of Dead Beat and Model Predictive controllers for this application and scrutinises the technical advantages and potential application issues of these methodologies. Moreover an improvement to the standard Model Predictive Control algorithm that include an intrinsic modulation scheme inside the controller and named Modulated Model Predictive Control is introduced. Detailed technical work is supported by Matlab/Simulink model based simulations and validated by experimental work on two converter platforms, considering both ideal and non-ideal electrical network conditions.

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Pou, Félix Josep. "Modulation and control of three-phase PWM multilevel converters." Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/6327.

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La present tesi doctoral estudia els inversors trifàsics multinivell del tipus denominat de díodes de fixació (diode-clamped converters). Aquests convertidors poden generar tres o més nivells de tensió a cada fase de sortida, i normalment s'apliquen a sistemes de gran potència ja que poden treballar amb tensions majors que els inversors clàssics. L'anàlisi es centra fonamentalment en la topologia de tres nivells, tot i que també es realitzen contribucions per a convertidors de més nivells. Els principals objectius són la proposta de nous algorismes de modulació vectorial PWM de processat ràpid, l'estudi i la compensació dels efectes dels desequilibris de les tensions dels condensadors del bus de continua, i l'anàlisi de llaços de control avançat.
S'han desenvolupat diversos models que han permès obtenir resultats de simulació de les tècniques de modulació i control proposades. A més, gràcies a l'estada d'un any de l'autor al Center for Power Electronics Systems (CPES) a Virginia Tech, USA, la tesi també inclou resultats experimentals que consoliden les conclusions i metodologies presentades. Les principals contribucions es resumeixen a continuació.
Es presenta un nou algorisme de modulació vectorial PWM que aprofita simetries del diagrama vectorial per a reduir el temps de processat. S'analitzen i es quantifiquen les oscil·lacions de tensió de baixa freqüència que apareixen en el punt central dels condensadors del convertidor de tres nivells. Aquesta informació permet dimensionar els condensadors donades les especificacions d'una determinada aplicació.
L'algorisme de modulació també s'aplica a convertidors de més nivells. Pel cas concret del convertidor de quatre nivells, es comprova l'existència de corrents continus en els punts mitjos dels condensadors que fan que els sistema sigui inestable. Es determinen gràficament les zones d'inestabilitat.
Es presenta un nou i eficient algorisme de modulació vectorial feedforward en el convertidor de tres nivells que és capaç de generar tensions trifàsiques de sortida equilibrades, malgrat l'existència de desequilibris en les tensions dels condensadors.
S'estudien els efectes negatius de càrregues lineals desequilibrades i càrregues no lineals en el control de les tensions dels condensadors. Es justifica que l'existència d'un quart harmònic en els corrents de càrrega pot inestabilitzar el sistema. És determina la màxima amplitud tolerable d'aquest harmònic.
S'estudia la millora en l'equilibrat de les tensions d'una connexió de dos convertidors de tres nivells al mateix bus de continua (back-to-back connection). Un exemple d'aplicació pràctica és la conversió AC/DC/AC per a l'accionament de motors d'alterna treballant amb factor de potència unitari.
Finalment s'aplica un controlador òptim al convertidor de tres nivells treballant com a rectificador elevador (boost). El llaç de control LQR (Linear Quadratic Regulator) es simplifica donat que la tasca d'equilibrat de les tensions dels condensadors es dur a terme en el mateix modulador.

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Kumar, Pavan M. R. "Analysis, design and control of a hybrid multilevel switching converter for synchrotron ring-magnet power." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. https://dspace.library.uvic.ca//handle/1828/9708.

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This thesis presents the development of a Hybrid Multilevel Switching Converter (HMSC) for Ring-Magnet Power Supplies (RMPS). The thesis includes the analysis, design and control of the proposed converter. It introduces multilevel switching converters to the field of ring-magnet power supplies. RMPS feed the electromagnets that produce the magnetic field required to energize and guide subatomic particles in a synchrotron. The accuracy and extreme precision of this magnetic field imposes stringent restrictions on the design and performance of the RMPS used. Study of conventional power supplies highlights the need for modern power supply solutions which can meet the specifications of RMPS. The complete frequency-domain analysis of the conventional resonant-type RMPS along with the Energy Make-up Unit (EMU) is presented. The resonant frequency drift is identified as the main factor in the design of the EMU. The analysis of the input filter network is presented for development of design criteria for input filter components. The principle advantages and disadvantages of the resonant-type RMPS are summarized before identifying multilevel converters as a viable option among switching converters for a non-resonant type of RMPS. The Hybrid Multilevel Switching Converter (HMSC) is proposed as a non-resonant type RMPS to overcome the disadvantages of the resonant-type RMPS. The operational features of the HMSC are explained and the simplification of the general HMSC configuration for positive output currents is identified. The steady-state analysis of the HMSC develops comprehensive design criteria for the device ratings and component stresses, including the methods for reducing the switching losses in the HMSC. Multilevel converters encounter voltage balancing problem among the DC-link capacitors. It is shown that the HMSC configuration is versatile in minimizing this problem. Harmonic spectrum of the output voltage of the HMSC is derived and the effect of number of output voltage levels in reducing the harmonic contents is established. A detailed survey of different current control techniques is presented to form the background for developing an effective current control algorithm for multilevel converters. A dead-beat current control strategy is chosen as an appropriate control technique to suit the needs of RMPS. The control scheme is extended to the control of multilevel converters in general. The control algorithm is developed to track a given arbitrary current reference signal for both single-variable and multi-variable systems. It is also shown that the output dead-beat control is a special case of the pole placement technique. The transient behaviour of the system has been studied and stability considerations of the system are examined. Extensive computer simulation studies have been performed using SABER to study the reference tracking nature of the proposed control scheme. The output current of the HMSC using the modified dead-beat control scheme is shown to follow a given arbitrary-reference with very small tracking error. The reference tracking nature has been simulated for a simple RL magnet load and a magnet load with LCR filter. Experimental results obtained from a laboratory prototype of the HMSC with an RL load, have been presented to substantiate the analytical results. Criteria for improvement in the reference tracking properties of the proposed system have been identified.
Graduate

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Molepo, Seaga Abram. "A multilevel inverter for DC reticulation." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53253.

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Thesis (MScEng)--Stellenbosch University, 2003.
ENGLISH ABSTRACT: This report presents the design and development of a multilevel inverter for DC reticulation. Two main multilevel inverter topologies are introduced and discussed. The research focusses on the flying capacitor multilevel topology, since it became evident that it is more suitable for DC reticulation than the diode clamped multilevel topology. A bootstrap power supply for the gate drive circuits of a multilevel inverter is developed and its feasibility verified experimentally. A self-starting auxiliary power supply, that aims at addressing the power supply problem of DC to AC and DC to DC converters, is designed and its functionality demonstrated on a flying capacitor multilevel inverter. An FPGA based digital controller for implementing the inverter's control algorithms is also discussed. This controller incorporates a feed-forward output voltage regulation technique. Experimental results obtained with the four-level flying capacitor multilevel inverter, using the FPGA based digital controller and the self-starting auxiliary power supply, are presented in this report.
AFRIKAANSE OPSOMMING: In hierdie verslag word die ontwerp en ontwikkelling van 'n multivlak omsetter vir GS retikulasie bespreek. Twee hoof multivlak omsetter topologië word voorgestel en bespreek. Die navorsing fokus op die "vlieënde-kapasitor" multivlak topologië omdat dit duidelik geword het dat dit 'n beter opsie is vir die GS retikulasie as die diode-klamp multivlak topologië. 'n Kragbron vir die hekaandryfbane van die multivlak omsetter is ontwikkel en die werking daarvan is met experimentele toetse bevestig. 'n Self-begin kragbron, wat die probleem van die kragtoevoer aan die GS na WS en die GS na GS omsetters aanspreek, is ontwerp en die funksionaliteit is gedemonstreer met die "vlieënde-kapasitor" multivlak . omsetter. 'n Digitale beheerder, gebaseer op 'n FPGA, wat gebruik word om die omsetter se beheer algoritmes te implementeer, word ook bespreek. Hierdie beheerder inkorporeer 'n vorentoe-voer uittree spannings regulasie tegniek. Eksperimentele resultate wat gekry is met 'n vier-vlak "vlieënde-kapasitor" multivlak omsetter, wat van die FPGA gebaseerde digitale beheerder en die self-begin kragbron gebruik maak, word ook in die verslag bespreek.

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Paterakis, Fotis Konstantinos. "Development of alternative pulse width modulation methods for conventional and multilevel voltage source inverters." Thesis, Brunel University, 2016. http://bura.brunel.ac.uk/handle/2438/13856.

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Multilevel inverters have attracted wide interest in both the academic community and the industry for the past decades. Therefore, the investigation and development of modulation strategies in multilevel inverters emerges as a necessity for the industry and researchers. In this doctoral thesis, alternative modulation methods suitable for three-level conventional single-phase inverters and especially for cascade H-bridge multilevel inverters are discussed and proposed. The theory of Equal Areas is reformed and presented and its modifications are proposed. These modifications are compared with other well-known modulation schemes, such as carrier-based modulation schemes and programmed pulse width modulation techniques. The advantage of the modified Equal Areas Pulse Width Modulation (EAPWM) is its algorithmic simplicity due to simple algebraic relationships, which results in less computational effort. A fully mathematical formulation for the Equal Areas modulation is proposed for both conventional and multilevel inverters. The EAPWM is shown to produce well-formed switched output voltages that have low total harmonic distortion at even low switching frequencies. The importance of this thesis is complimented by the results, produced after the implementation of EAPWM in multilevel inverters, which can be used as a more accurate reference when compared with other modulation strategies. Moreover, this direct modulation strategy has been extended to work on higher amplitude modulation ratios, in a linear manner, while entering the over modulation region. In this context, modified algorithms have been developed using different criteria for the calculation of the pulses’ width and their placement inside the time interval. The equal areas method, implemented in conventional single-phase inverters, uses odd pulse numbers per half cycle, holding integer frequency ratios in contrast to its implementation in multilevel inverters, where non-integer frequency ratios occur due to the level-by-level application. The application of the method is verified by simulations together with experimental work using a full-scale prototype inverter.

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Lee, G. B. "A practical comparison between the three-phase series-stacked and neutral point clamped multilevel converter topologies." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53287.

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Thesis (MScEng)--Stellenbosch University, 2003.
ENGLISH ABSTRACT: The versatility of power electronic converters has made them a dominant force in the current electrical and electronic engineering industry. So too industry presents a wider range of applications, forever demanding operation at higher power levels. To meet this need a variety of multilevel converters have evolved. The challenge often lies in the selection of the appropriate topology for a specific application. This thesis presents a practical comparison between the Series-Stacked and Neutral Point Clamped multilevel converter topologies as candidates for Medium Voltage Direct Current and Traction applications. Their configurations, characteristics, switching techniques and practical performances are compared, in order to aid the topology selection process.
AFRIKAANSE OPSOMMING: As gevolg van die veelsydigheid van drywings elektroniese omsetters word dit geimplementeer in n toenemende hoeveelheid toepassings met toenemende drywings vlakke in die elektriese en elektroniese industrie. Om aan hierdie behoefte te voorsien het n reeks veelvlak omsetters ontstaan. Die uitdaging hiermee is die keuse van die toepaslike topologie vir n spesifieke doelwit. Hierdie proefskrif vergelyk die Serie Gekoppelde en die Geklemde Neutrale Punt omsetters ten opsigte van konfigirasie, karakteristieke, skakel tegnieke en praktiese werksverrigting om die toepaslikheid te bepaal vir Medium Spanning Gelykstroom en Traksie toepassings.

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Song, Byeong-Mun. "Voltage Balancing Techniques for Flying Capacitors Used in Soft-Switching Multilevel Active Power Filters." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/30026.

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This dissertation presents voltage stabilization techniques for flying capacitors used in soft-switching multilevel active power filters. The proposed active filter has proved to be a solution for power system harmonics produced by static high power converters. However, voltage unbalance of the clamping capacitors in the active filter in practical applications was observed due to its unequal parameters. Thus, the fundamentals of flying capacitors were characterized dealing with voltage balancing between flying capacitors and dc capacitors under practical operation, rather than ideal conditions. The study of voltage balancing provides the fundamental high-level solutions to flying capacitor based multilevel converter and inverter applications without additional passive balancing circuits. The use of proposed voltage balancing techniques made it possible to have a simple structure for solving the problems associated with the conventional bulky passive resistors and capacitor banks. Furthermore, the proposed control algorithms can be implemented with a real time digital signal processor. It can achieve the high performance of the active filter by compensating an adaptive gain to the controller. The effectiveness of the proposed controller was confirmed through various simulations and experiments. The focus of this study is to identify and develop voltage stabilization techniques for flying capacitors used in a proposed active filter. The voltage unbalance is investigated and characterized to provide safe operations. After having defined the problems associated with the voltage unbalance, the most important voltage stabilization techniques are proposed to solve this problem, in conjunction with an instantaneous reactive power (IRP) control of an active filter. In order to reduce the switching losses and improve the efficiency of the active filter, the proposed soft-switching techniques were evaluated through simulation and experimentation. Experimental results indicate that the proposed active filter achieved zero-voltage conditions in all of the main switches and zero-current turn-off conditions to the auxiliary switches during commutation processes. Also, various studies on soft-switching techniques, multilevel inverters, control issues and dynamics of the proposed active filter are discussed and analyzed in depth.
Ph. D.

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Nampally, Ashok. "Investigation of modulation dynamics and control of modular multilevel converter for high voltage DC grids." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=235573.

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Energy security concerns and the impact of traditional sources of power generation on the climate have prompted a rise in renewable energy expansion around the world. Power transmission from remote generation sites to consumers over long distance is most efficient using High-Voltage Direct Current (HVDC) transmission lines. Consequently, HVDC and the integration of renewable resources are considered as key perspectives in the improvement of sustainable energy systems capable of secure and stable electric power supply. With the intention of huge energy demand in the future, the multi-terminal DC grid concept is proposed based on various converter topologies like Line Commutated Converter (LCC), Voltage Sourced Converter (VSC), and Modular Multilevel Converter (MMC) HVDC technologies. These converters play a vital role in integrating remotely-located renewable generation and reinforcing existing power systems. The MMC has become increasingly popular in HVDC transmission compared to conventional line commutated converters, two-level and multilevel voltage source converters. Low generation of harmonics, a low switching frequency of semiconductors, sine formed AC voltages and currents, black start capability and higher overall efficiency are a few of the unique features of MMC. The MMC is characterised by a modular arm structure, formed by a cascade connection of a vast number of simple cells with floating DC capacitors. These cells are called Sub-Modules (SMs) and can be easily assembled into a converter for high voltage power conversion systems. Compared with traditional VSCs, the analytical modelling of MMC is more challenging. This is because of technical issues such as higher order system, the discontinuous and non-linear nature of signal transfer through converters, the complexity of the interaction equations between the AC and DC variables, and harmonic frequency conversion through AC side and DC side of the converter. This work intends to resolve these challenges by developing a detailed non-linear model using fundamental switching Selective Harmonic Elimination (SHE) modulation technique, an average MMC model in DQ0 frame and an analytical dynamic MMC model, which can be suitable for small-signal stability studies, and control design. Firstly, the detailed model of MMC using fundamental switching SHE modulation scheme has been developed using PSCAD/EMTDC (Power systems computer aided design Electromagnetic transients for DC) software. The basic terms and equations of the MMC have been presented along control loops. The significance of the switching frequency on the performance of the MMC has been studied as well as the relation between the switching frequency, the Total Harmonic Distortion (THD) and the number of output voltage levels. Detailed representation of MMC systems in PSCAD/EMTDC programs incorporates the modelling of Insulated-Gate Bipolar Transistor (IGBT) valves and should typically utilise small integration time-steps to represent fast switching events precisely. Computational burden introduced by such detailed models make the study of steady-state and transient events more complex, highlighting the need to implement more efficient models that provide comparative behaviour and dynamic response. Secondly, average DQ0 models has been implemented to accurately replicate the steady-state, dynamic and transient behaviour of MMC in PSCAD/EMTDC programs. These simplified models represent the average response of switching devices and converters by using averaging techniques involving controlled sources and switching functions. Developing the MMC average model in DQ0 frame was a challenging task because of the multiplication terms in the MMC average model in ABC frame. The proposed approach to overcome this challenge is considering generic form for the product variables and multiplying them in ABC frame and then transferring only the DC and fundamental frequency components of the results to DQ0 frame. The comparisons between detailed model and the average model validated the effectiveness of the average model in representing the dynamics of MMC. It is at least one hundred times faster than the detailed model for the same simulation time step. Finally, a dynamic analytical MMC model and associated controls have been proposed. To enable the model application to a broad range of system configurations and various dynamic studies, the model is built on a modular modelling approach using four sub-systems; an AC system, Phase Locked Loop (PLL) system, MMC system and a DC arrangement. The developed MMC system model has been linearized and implemented in state-space form. To select the best open-loop controller gains, eigenvalue analysis is performed for each particular test system. The rationality and correctness of the proposed model are verified against non-linear PSCAD/EMTDC simulations, and good accuracy is obtained in the time domain analysis. Further, the model is also verified in the frequency domain, and it is concluded that the developed model can be employed for dynamic analysis below 300 Hz.

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ABDELHAMID, ESLAM. "Innovative Digital dc-dc Architectures for High-Frequency High-Efficiency Applications." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3427310.

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The new generation of automotive controllers requires a space-constrained and high-efficiency step-down architecture. Hence, recently a potential alternative for the conventional step-down topologies is highly demanded. The new architecture should meet the high power density, high efficiency, wide operating ranges, high EMI capabilities, and low-cost requirements. This thesis, developed at the University of Padova and sponsored by Infineon Technologies, aims at investigating potential candidate topologies for automotive step-down conversion capable of eliminating or offsetting some of the common shortcomings of conventional solutions currently in use. Many research effort is paid for the soft switching quasi-resonant topologies in order to miniaturize the passive components through the switching frequency increase. However, the variable switching frequency, increased components count, and narrow operating ranges prevent the wide adoption of the quasi-resonant topologies in the target application. The first objective of this project is to investigate the quasi-resonant buck converter topology in order to stand on the limitations and operating conditions boundaries of such topology. The digital efficiency optimization technique, which is developed in this work, extends the operating ranges in addition to reduce operating frequency variations. On the other hand, the multilevel hybrid topologies are potentially able to meet the aforementioned requirements. By multiplying ripple frequency and fractioning voltage across the switching node the multilevel topologies have the direct advantage of reduced passive components. Moreover, multilevel topologies have many other attractive features include reduced MOSFET voltage rating, fast transient response, a Buck-like wide range voltage conversion ratio, and improved efficiency. These features candidate the multilevel topologies, in particular, the three-level flying-capacitor converter, as an innovative alternative for the conventional topologies for the target application. Accordingly, the three-level flying-capacitor converter (3LFC) is investigated as a second objective for this project. Flying-capacitor (FC) voltage balancing in such topology is quite challenging. The 3LFC under valley current mode control shows an interesting performance, where the FC voltage is self-balanced. In this work, the stability of the converter under valley and peak current mode control is studied and a simplified stability criterion is proposed. The proposed criterion address both current loop static stability and FC voltage stability. The valley current mode modulator results to be inherently stable as soon as the current static instability is compensated with an external ramp. On contrary, the FC voltage in peak current mode control (P-CMC) will never be balanced unless the converter operated with relatively high static peak-to-peak inductor current ripple. Since P-CMC has an inherent over-current protection feature, P-CMC based architectures are widely used in the industrial applications. However, in practice the peak current controlled three-level converter is inherently unstable. Consequently, the instability of the P-CMC 3LFC is addressed. A sensorless stabilizing approach, with two implementation methodologies, is developed in this work. The proposed technique eliminates the instability associated with the FC voltage runaway, in addition to FC voltage self-balancing. Moreover, the proposed methodology offers reduced size, less complexity, and input voltage independent operation. Besides, the proposed approach can be extended to system with a higher number of voltage levels with minimal hardware complexity. The proposed techniques and methodologies in this work are validated using simulation models and experimentally. Finally, in the conclusions the results of the Ph.D. activity are summarized and recommendations for the further development are outlined.

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Louganski, Konstantin. "Generalized Average-Current-Mode Control of Single-Phase AC-DC Boost Converters with Power Factor Correction." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/27331.

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The dissertation presents a generalized average-current-mode control technique (GACMC), which is an extension of the average-current-mode control (ACMC) for single-phase ac-dc boost converters with power factor correction (PFC). Traditional ACMC is generalized in a sense that it offers improved performance in the form of significant reduction of the current control loop bandwidth requirement for a given line frequency in unidirectional and bidirectional boost PFC converters, and additional functionality in the form of reactive power control capability in bidirectional converters. These features allow using a relatively low switching frequency and slow-switching power devices such as insulated-gate bipolar transistors (IGBTs) in boost PFC converters, including those designed for higher ac line frequencies such as in aircraft power systems (360â 800 Hz). In bidirectional boost PFC converters, including multilevel topologies, the GACMC offers a capability to supply a prescribed amount of reactive power (with leading or lagging current) independently of the dc load power, which allows the converter to be used as a static reactive power compensator in the power system.

A closed-loop dynamic model for the current control loop of the boost PFC converter with the ACMC has been developed. The model explains the structure of the converter input admittance, the current phase lead phenomenon, and lays the groundwork for development of the GACMC. The leading phase admittance cancellation (LPAC) principle has been proposed to completely eliminate the current phase lead phenomenon and, consequently, the zero-crossing distortion in unidirectional converters. The LPAC technique has been adapted for active compensation of the input filter capacitor current in bidirectional boost PFC converters.

The dynamic model of the current control loop for bidirectional boost PFC converters was augmented to include a reactive power controller. The proposed control strategy enables the converter to process reactive power and, thus, be used as a reactive power compensator, independently of the converter operation as an ac-dc converter.

Multiple realizations of the reactive power controller have been identified and examined in a systematic way, along with their merits and limitations, including susceptibility to the ac line noise. Frequency response characteristics of reactive elements emulated by means of these realizations have been described.

Theoretical principles and practical solutions developed in this dissertation have been experimentally verified using unidirectional and bidirectional converter prototypes. Experimental results demonstrated validity of the theory and proposed practical implementations of the GACMC.
Ph. D.

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Rech, Cassiano. "Análise, projeto e desenvolvimento de sistemas multiníveis híbridos." Universidade Federal de Santa Maria, 2005. http://repositorio.ufsm.br/handle/1/3703.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This Ph.D. Dissertation presents contributions to the study of hybrid multilevel systems, analyzing several issues that compose this system, such as: topological variations of the output inverter stage and input rectifier stage, design methodologies, modulation strategies and control system. This extensive analysis is carried out because these issues are closely related, so that a modification in any element can affect the overall system performance. Initially, due to the enormous flexibility and large complexity to design hybrid multilevel converters, this work proposes a unified analysis for these converters, which are composed of several series-connected cells with distinct voltage levels, modulation strategies, topologies and/or semiconductor technologies. This unified analysis includes a detailed comparative analysis among distinct topologies and a new generalized design methodology. Different configurations of hybrid converters are proposed from this new design methodology, depending on the specifications imposed to the multilevel system. Therefore, this work can be used as a valuable tool to define an adequate hybrid configuration for a specific application. After, this work also proposes a new arrangement to implement the isolated voltage sources of the series-connected cells that compose a hybrid multilevel inverter. This new arrangement is based on the multipulse connection of uncontrolled rectifiers processing distinct power levels, unlike conventional multipulse converters. A new design methodology for this input stage is proposed in this work, defining the phase shifts among the secondaries of the isolation transformer to eliminate dominant harmonics from the current drawn from the utility grid even when the active power levels processed by rectifiers are different. This work also investigates the impact of the hybrid multilevel modulation strategy on the harmonic contents of the output voltages and input currents. After to demonstrate the negative impact of the modulation strategy on the input harmonic performance for some operating points, this Ph.D. Dissertation proposes a new modulation strategy that makes possible, together with an asymmetrical multipulse connection of rectifiers, to eliminate undesired harmonics from the input current in any operating point without affecting the output harmonic performance. Beyond these issues, this work also includes a qualitative analysis about hybrid multilevel inverters operating as actuators in closed-loop systems, to motivate a discussion about this new subject. Finally, several experimental results are presented to demonstrate the practical feasibility of some proposals of this Ph.D. Dissertation.
Esta Tese de Doutorado apresenta contribuições ao estudo de sistemas multiníveis híbridos, investigando vários temas que compõem esse sistema, tais como: variações topológicas do estágio inversor de saída e do estágio retificador de entrada, metodologias de projeto, estratégias de modulação e sistema de controle. Isso se deve principalmente ao fato que esses temas estão intimamente relacionados, de tal forma que uma alteração em qualquer elemento do sistema pode modificar o desempenho do todo. Inicialmente, devido à enorme flexibilidade e grande complexidade para projetar conversores multiníveis híbridos, esse trabalho realiza uma abordagem unificada desses conversores, que são compostos de várias células em série, com valores de tensão, estratégias de modulação, topologias e/ou tecnologias de semicondutores diferentes. Essa abordagem inclui uma análise comparativa entre várias topologias e uma nova metodologia de projeto generalizada. Assim, esse trabalho pode ser usado como uma importante ferramenta para definir um conversor híbrido adequado para uma determinada aplicação. Posteriormente, esse trabalho também propõe um novo arranjo para implementar as fontes de tensão isoladas das células que compõem um inversor multinível híbrido. Esse novo arranjo é baseado na conexão multipulso de retificadores não controlados que, ao contrário dos conversores multipulso convencionais, processam níveis distintos de potência. Uma nova metodologia de projeto generalizada é proposta nesse trabalho para esse estágio de entrada, determinando os ângulos de defasagem entre os secundários do transformador de isolação para eliminar harmônicas dominantes da corrente drenada da rede pública de energia, mesmo quando os retificadores processam níveis distintos de potência ativa. Esse trabalho também investiga o impacto da estratégia de modulação híbrida tanto no conteúdo harmônico das tensões de saída quanto no conteúdo harmônico das correntes de entrada. Após demonstrar o impacto negativo da estratégia de modulação no desempenho harmônico de entrada em alguns pontos de operação, essa Tese propõe uma nova estratégia de modulação que torna possível, juntamente com uma conexão multipulso assimétrica de retificadores, eliminar harmônicas dominantes da corrente de entrada em qualquer ponto de operação sem prejudicar o conteúdo harmônico das tensões de saída. Além desses assuntos, esse trabalho também realiza uma breve análise qualitativa do desempenho de inversores multiníveis híbridos em sistemas de controle em malha fechada, com o intuito de iniciar uma discussão sobre esse novo tema. Por fim, diversos resultados experimentais, tanto do estágio inversor de saída quanto do estágio retificador de entrada, são apresentados para demonstrar a viabilidade prática de algumas propostas dessa Tese de Doutorado.

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Zambra, Diorge Alex Báo. "Análise comparativa de inversores multiníveis com células h-bridge conectadas em série." Universidade Federal de Santa Maria, 2006. http://repositorio.ufsm.br/handle/1/8467.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This Master Thesis presents a methodology to compare different topologies and configurations of multilevel systems applied to drive medium voltage induction motors. Initially, it presents the input and output parameters that must be supplied by the power drivesystems manufacturer. Then, the mathematical models of the performance indexes used are presented, being, the total harmonic distortion, first order distortion factor and the power losses of the main semiconductors devices. After, it is presented a methodology that allows the amplitude selection of DC sources for the inverter with a specific number of cascaded Hbridge cells. A study regarding the hybrid multilevel modulation strategies and the impact of their variations on the semiconductors devices power losses of the output inverter is developed. Based on this study, it is proposed a new hybrid multilevel modulation technique, it minimizes the semiconductors power losses and allow the use of front-end uncontrolled rectifiers without modifying the total harmonic distortion of the output voltage inverter. After, it is developed a comparative study between the asymmetrical hybrid multilevel inverter and the symmetrical multilevel inverter, which enables the determination of the switching frequency for the one determined performance and the maximum switching frequency of each converter. This Master Thesis presents complementary methods of design of the hybrid multilevel inverter and a methodology that will make possible to choose the drive system that presents high efficiency and reduced cost, neither penalizing the energy quality of the utility grid nor the induction motor constraints.
Esta Dissertação de Mestrado apresenta uma metodologia para comparar diferentes topologias e configurações de sistemas multiníveis aplicados ao acionamento de motores de indução de média tensão. Inicialmente são apresentados os parâmetros de entrada e saída que devem ser fornecidos pelos fabricantes de sistemas de acionamento de alta potência. Então, são apresentados os modelos matemáticos dos índices de desempenho utilizados, sendo eles, distorção harmônica total, fator de distorção de primeira ordem e perdas nos dispositivos semicondutores principais. Posteriormente, é apresentada uma metodologia que permite selecionar a amplitude das fontes CC para um inversor com um número específico de células H-bridge conectadas em série. Um estudo a respeito das estratégias de modulação multinível híbrida e o impacto de suas variações sobre as perdas dos dispositivos semicondutores do inversor de saída é apresentado. Fundamentado neste estudo, é proposta uma nova técnica de modulação multinível hibrida, que minimiza as perdas nos semicondutores e permite o uso de retificadores não controlados no estágio de entrada sem modificar a distorção harmônica total da tensão de saída do inversor. Depois, é desenvolvido um estudo comparativo entre o inversor multinível híbrido assimétrico e o inversor multinível simétrico, que permite a determinação da freqüência de comutação para um rendimento específico e a máxima freqüência de comutação de cada conversor. Esta Dissertação de Mestrado apresenta métodos complementares de projeto de inversores multiníveis híbridos e uma metodologia que possibilitará escolher sistemas de acionamento que apresentem alta eficiência e custo reduzido, sem por isso prejudicar a qualidade da energia drenada da rede pública e fornecida ao motor de indução.

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Morati, Mathieu. "Contribution à l'étude et au contrôle des convertisseurs multiniveaux : application à la compensation des fours à arc." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0052/document.

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Cette thèse est dédiée aux convertisseurs multiniveaux et aborde les problématiques liées à la compensation des perturbations générées sur un réseau électrique, telles que celles produites par les fours à arc. Elle est composée de quatre chapitres couvrant les thématiques de la modélisation des réseaux électriques, des convertisseurs de tension, du contrôle commande et des stratégies de compensation, accompagnés de simulations et de résultats expérimentaux obtenus sur des équipements industriels de forte puissance. Les applications réseaux étant diverses et variées, les convertisseurs multiniveaux sont ici étudiés dans le but d’être raccordés directement sur des réseaux de distribution. Pour cela, un état de l’art des différentes topologies de convertisseurs de tension (classiques et multiniveaux) est présenté et les topologies dites modulaires, sont retenues pour une étude plus poussée. Ces convertisseurs utilisent des modules de puissance à base de ponts en H, de ½ ponts en H ou de ponts en H 3-niveaux connectés en cascade. Ils permettent ainsi de créer différents types de configurations ou couplages appelés dans ce mémoire : étoile, triangle et étoiles symétriques. Les différents modules et les stratégies pour les commander sont étudiés autour d’un composant de puissance (de type IGBT 2.5kV/1.5kA). A travers les domaines électrique et thermique, une méthode est proposée afin d’estimer les pertes, les températures de jonction et déterminer ainsi les limites d’utilisation d’un tel composant de puissance. Le dimensionnement et la fiabilité de ces convertisseurs est également abordé pour chacune des configurations envisagées, afin de dégager les avantages et inconvénients pour une application réseau. D’une façon générale, la stratégie de contrôle des convertisseurs multiniveaux est ardue, principalement lié au fait que de multiples sources de tensions continues doivent être contrôlées. Dans cette optique, des stratégies de contrôle sont proposées et validées en simulation selon les types de modules et de configurations utilisés pour la compensation des perturbations d’un four à arc. Enfin, la dernière partie de ces travaux est consacrée aux résultats expérimentaux sur la base d’un compensateur industriel dénommé DSVC (Dynamic Static Var Compensator), pour la compensation des fours à arc. Les différents résultats obtenus sur plusieurs sites industriels ont ainsi permis la validation des travaux exposés dans ce mémoire
This thesis is dedicated to the multilevel converters and addresses issues related to compensation for disturbance generated on an electrical network such as those produced by arc furnaces. It is composed of four chapters covering the themes of modeling of electrical networks, voltage converters, control and compensation strategies, with simulations and experimental results obtained on high power industrial equipment. There are many networks applications and multilevel converters are here considered to be directly connected to distribution networks. Therefore, a state of the art of different voltage converters, classics and multilevel topologies, is presented and the topologies called modular are retained for further studies. These converters use modular power cells made of H bridges, ½ bridges or 3-level H bridges connected in cascade. They allow to create different types of configurations or couplings called in this memory: star, delta and double stars. The different modules and the strategies to control them are investigated around the same switching power component (IGBT 2.5kV/1.5kA). Through electrical and thermal fields, a method is proposed to estimate their losses, junction temperatures in order to determine the limits of use of such a component of power. Sizing and reliability of these converters is also discussed for each considerer configurations in order to identify the advantages and disadvantages for a network application. Generally, the multilevel converters control strategy is difficult because of the multiple sources of DC voltages to control. In this context, control strategies are proposed and validated in simulation according to the types of modules and configuration used to compensation for disturbance of an arc furnace. Finally, the last part of this thesis is devoted to the experimental results based on an industrial compensator DSVC (Dynamic Static Var Compensator) for arc furnace compensation. The different results obtained at several industrial sites have thus allowed the validation of the various works exposed in this thesis

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Brandelero, Julio Cezar. "Conception et réalisation d'un convertisseur multicellulaire DC/DC isolé pour application aéronautique." Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/14246/1/Brandelero.pdf.

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L’électricité prend une place de plus en plus importante dans les systèmes énergétiques embarqués. L’électricité est une forme d’énergie très malléable, facile à transporter et réglable ou transformable avec un très faible taux de pertes. L’énergie électrique, associée à des convertisseurs statiques, est plus facile à maîtriser que, par exemple, l’énergie hydraulique et/ou pneumatique, permettant un réglage plus fin et une réduction des coûts de maintenance. L’évolution de la puissance dans les modèles avioniques est marquante. Avec le nombre croissant de charges électroniques, un avion plus électrique avec un réseau à courant alternatif inclurait un grand nombre de redresseurs AC/DC qui devront respecter les normes de qualité secteur. Une solution pour la réduction de la masse serait de préférer un réseau HVDC (High Voltage DC Bus). Sur les futurs modèles avioniques plus électriques, les concepteurs envisageront des conversions HVDC/DC à partir de l’unité appelée BBCU (Buck Boost Converter Unit). Dans ce cas d’étude, un réseau de distribution en tension continue (±270Vdc) est connecté à un réseau de sécurité basse tension (28Vdc) avec un échange bidirectionnel de puissance pouvant atteindre 10kW. Le convertisseur statique assurant cette liaison représente de nouveaux défis pour l’électronique de puissance en termes de fiabilité, sûreté, détection de panne, rendement et réduction de masse et de coût. Le dimensionnement du convertisseur doit prendre en compte une conception optimale, en aéronautique ce critère est la masse. Dans le processus de dimensionnement et d’optimisation du convertisseur, il est donc impératif de prendre en compte trois facteurs principaux : 1) l’évolution des topologies de conversion, 2) l’évolution des composants actifs et passifs et 3) l’intégration de puissance. La réunion de ces trois facteurs permettra ainsi la miniaturisation des convertisseurs statiques. Dans un premier temps, nous préciserons la démarche adoptée pour le dimensionnement d’un convertisseur en prenant en compte : les topologies actives, les filtres différentiels et le système de refroidissement. Les différents éléments qui composent le convertisseur sont décrits dans un langage informatique orienté objet. Des facteurs de performances seront également introduits afin de faciliter le choix des semi-conducteurs, des condensateurs et du dissipateur pour un convertisseur statique. Dans un deuxième temps, nous présenterons le fonctionnement d’une topologie multicellulaire DC/DC, isolée pour l’application proposée. Nous présenterons les avantages du couplage de différentes phases de ce convertisseur. Nous introduirons les différentes associations des cellules et leurs avantages, possibles grâce à l’isolement, comme la mise en série et en parallèle. Puisque la caractérisation des pertes des semi-conducteurs est essentielle pour le dimensionnement du convertisseur statique, nous proposerons deux approches : un modèle de simulation relativement simple et paramétré à l’aide de seules notices constructeurs ; et une méthode de mesure des pertes dans les semi-conducteurs qui est à la fois précise et compatible avec les composants les plus rapides. En ce qui concerne les composants magnétiques, une surface de réponse des matériaux ferrites sera présentée. Nous allons décrire, par le biais analytique et de simulation, des modèles pour la détermination du champ magnétique à l’intérieur du noyau et des ondulations de courant engendrés. Finalement, en profitant des modèles et des résultats obtenus dans les sections précédentes, nous montrerons le dimensionnement et la réalisation de chaque partie du convertisseur BBCU 100kHz / 10kW. Une perspective d’un design idéal est également présentée.

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Boutry, Arthur. "Theoretical and experimental evaluation of the Integrated gate-commutated thyristor (IGCT) as a switch for Modular Multi Level Converters (MMC)." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI095.

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Une étude sur la réduction/suppression de l'inductance de limitation di/dt pour IGCTs et du clamp RCD en utilisant des diodes rapides en silicium (Si) et des diodes en carbure de silicium (SiC) dans les convertisseurs multiniveaux modulaires (MMC). Cette thèse contient :- Analyse des sous-modules de MMC HVDC existants.- Évaluation de l'intérêt des IGCTs dans les sous-modules MMC HVDC et comparaison des pertes avec les IGBT, en utilisant des facteurs de mérite spécifiques aux MMC créés dans cette thèse.- Test de double pulse avec diode à récupération rapide dans un module plastique pour tenter de réduire et supprimer l'inductance limitant le di/dt.- Packaging de puces de diodes SiC PiN à haute tension et courant élevé, test avec IGCT dans le même montage, pour tenter de réduire et supprimer l'inductance limite di/dt, et analyser les spécificités de la diode SiC dans ce montage
A study on Integrated gate-commutated thyristors (IGCT) di/dt limiting inductance and RCD-clamp reduction/suppression using plastic module silicon (Si) fast recovery diodes and silicon carbide (SiC) diodes, in Modular Multilevel Converters (MMC). This PhD contains:- Analysis of existing HVDC MMC Submodules.- Assessment of the interest of the IGCT in HVDC MMC Submodules and losses comparison with IGBTs, using MMC-specific figures-of-merit created in this thesis.- Double pulse test with fast recovery diode in plastic module to attempt to reduce and suppress the limiting di/dt inductor.- Packaging of High-Voltage High-Current SiC PiN diode dies, test with IGCT in the same setup to attempt to reduce and suppress the limiting di/dt inductor and analyze the specificities of the SiC diode in this setup

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Pozzebon, Giovani Guarienti. "Controle e análise de conversores multiníveis conectados em redes de distribuição para aplicação em painéis fotovoltaicos e armazenadores de energia." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-18072013-111105/.

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A utilização de conversores multiníveis tem sido uma importante alternativa para aplicações de alta potência e média tensão, graças aos altos níveis de potência alcançáveis por estas estruturas. Recentemente, esta topologia de conversores foi aplicada em sistemas com fontes alternativas para alimentar um sistema de geração distribuída, nos quais diferentes fontes de energia eram utilizadas. Com base nas características dos conversores multinível e sua potencial aplicabilidade em sistemas de geração distribuída, este trabalho tem como objetivo construir um sistema multinível conectado a rede de distribuição para utilização de fontes alternativas de energia como fontes primárias. Considerando que a energia fornecida pelas fontes alternativas pode sofrer variações, propõe-se a integração de sistemas armazenadores de energia, como capacitores, ao sistema multinível. Por isso, este trabalho desenvolve uma estratégia de controle para máxima transferência de potência ativa entregue à rede a fim de obter um fluxo ótimo. A topologia multinível deste trabalho possui em sua configuração dois módulos inversores conectados em série. Neste caso, é possível que pelo menos um desses inversores funcione com uma modulação em baixa frequência processando a maior parcela de potência. Assim, duas estratégias de controle modulação de fase e modulação de amplitude para a transferência de potência realizada pelo inversor de baixa frequência são analisadas. As vantagens e desvantagens de cada um dos métodos são expostas e então a estratégia mais adequada, no caso a modulação de amplitude, é utilizada na operação do conversor multinível. Além disso, são apresentados a modelagem das plantas e o projeto dos controladores de cada um dos módulos inversores. Por fim, a validação da proposta é feita através dos resultados de simulações e experimentais que mostram a capacidade do sistema de geração em transferir potência constante para a rede de distribuição e manter a corrente quase sem distorções em fase com a tensão.
The utilization of multilevel converters has been an important alternative for medium voltage applications with high power and power quality demand, thanks to the high power levels achievable for this kind of structure. Recently, this converter topology was proposed as a new possibility in renewable energy source applications, mainly in system delivering power to the grid, where different renewable energy resources may be used. Based on the characteristics of multilevel converters, and their potential applicability in distributed generation systems, this study aims to build a multilevel system that could be powered by renewable energy sources as primary sources and then connect them to a distribution grid. However, considering the energy produced by alternative sources can vary, it is analyzed the integration of a storage energy system in this multilevel topology. Taking into account this ends, the main concern of this study is related to the development of a control strategy to maximize the active power transferred to the grid. The multilevel topology employed in this study has two H-bridge inverter modules connected in series forming a cascaded configuration. Therefore, it is possible that at least one of these inverters, operating with a low frequency of modulation, process the majority of power with lower amount of losses. On this way, two control strategies for power transfer are analyzed. The advantages and disadvantages of each method are presented, and the most appropriated strategy is used in the operation of the multilevel converter system. In addition, it has been presented the design criteria for each controller and finally the validation of the proposed approach is done by mains of simulations and experimental results which show the ability of the converter to transfer constant active power to the grid and keep the grid current in phase with the grid voltage.

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Nami, Alireza. "A new multilevel converter configuration for high power and high quality applications." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/33216/1/Alireza_Nami_Thesis.pdf.

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The Queensland University of Technology (QUT) allows the presentation of theses for the Degree of Doctor of Philosophy in the format of published or submitted papers, where such papers have been published, accepted or submitted during the period of candidature. This thesis is composed of ten published /submitted papers and book chapters of which nine have been published and one is under review. This project is financially supported by an Australian Research Council (ARC) Discovery Grant with the aim of investigating multilevel topologies for high quality and high power applications, with specific emphasis on renewable energy systems. The rapid evolution of renewable energy within the last several years has resulted in the design of efficient power converters suitable for medium and high-power applications such as wind turbine and photovoltaic (PV) systems. Today, the industrial trend is moving away from heavy and bulky passive components to power converter systems that use more and more semiconductor elements controlled by powerful processor systems. However, it is hard to connect the traditional converters to the high and medium voltage grids, as a single power switch cannot stand at high voltage. For these reasons, a new family of multilevel inverters has appeared as a solution for working with higher voltage levels. Besides this important feature, multilevel converters have the capability to generate stepped waveforms. Consequently, in comparison with conventional two-level inverters, they present lower switching losses, lower voltage stress across loads, lower electromagnetic interference (EMI) and higher quality output waveforms. These properties enable the connection of renewable energy sources directly to the grid without using expensive, bulky, heavy line transformers. Additionally, they minimize the size of the passive filter and increase the durability of electrical devices. However, multilevel converters have only been utilised in very particular applications, mainly due to the structural limitations, high cost and complexity of the multilevel converter system and control. New developments in the fields of power semiconductor switches and processors will favor the multilevel converters for many other fields of application. The main application for the multilevel converter presented in this work is the front-end power converter in renewable energy systems. Diode-clamped and cascade converters are the most common type of multilevel converters widely used in different renewable energy system applications. However, some drawbacks – such as capacitor voltage imbalance, number of components, and complexity of the control system – still exist, and these are investigated in the framework of this thesis. Various simulations using software simulation tools are undertaken and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results. This thesis is divided into two main sections. The first section focuses on solving the capacitor voltage imbalance for a wide range of applications, and on decreasing the complexity of the control strategy on the inverter side. The idea of using sharing switches at the output structure of the DC-DC front-end converters is proposed to balance the series DC link capacitors. A new family of multioutput DC-DC converters is proposed for renewable energy systems connected to the DC link voltage of diode-clamped converters. The main objective of this type of converter is the sharing of the total output voltage into several series voltage levels using sharing switches. This solves the problems associated with capacitor voltage imbalance in diode-clamped multilevel converters. These converters adjust the variable and unregulated DC voltage generated by renewable energy systems (such as PV) to the desirable series multiple voltage levels at the inverter DC side. A multi-output boost (MOB) converter, with one inductor and series output voltage, is presented. This converter is suitable for renewable energy systems based on diode-clamped converters because it boosts the low output voltage and provides the series capacitor at the output side. A simple control strategy using cross voltage control with internal current loop is presented to obtain the desired voltage levels at the output voltage. The proposed topology and control strategy are validated by simulation and hardware results. Using the idea of voltage sharing switches, the circuit structure of different topologies of multi-output DC-DC converters – or multi-output voltage sharing (MOVS) converters – have been proposed. In order to verify the feasibility of this topology and its application, steady state and dynamic analyses have been carried out. Simulation and experiments using the proposed control strategy have verified the mathematical analysis. The second part of this thesis addresses the second problem of multilevel converters: the need to improve their quality with minimum cost and complexity. This is related to utilising asymmetrical multilevel topologies instead of conventional multilevel converters; this can increase the quality of output waveforms with a minimum number of components. It also allows for a reduction in the cost and complexity of systems while maintaining the same output quality, or for an increase in the quality while maintaining the same cost and complexity. Therefore, the asymmetrical configuration for two common types of multilevel converters – diode-clamped and cascade converters – is investigated. Also, as well as addressing the maximisation of the output voltage resolution, some technical issues – such as adjacent switching vectors – should be taken into account in asymmetrical multilevel configurations to keep the total harmonic distortion (THD) and switching losses to a minimum. Thus, the asymmetrical diode-clamped converter is proposed. An appropriate asymmetrical DC link arrangement is presented for four-level diode-clamped converters by keeping adjacent switching vectors. In this way, five-level inverter performance is achieved for the same level of complexity of the four-level inverter. Dealing with the capacitor voltage imbalance problem in asymmetrical diodeclamped converters has inspired the proposal for two different DC-DC topologies with a suitable control strategy. A Triple-Output Boost (TOB) converter and a Boost 3-Output Voltage Sharing (Boost-3OVS) converter connected to the four-level diode-clamped converter are proposed to arrange the proposed asymmetrical DC link for the high modulation indices and unity power factor. Cascade converters have shown their abilities and strengths in medium and high power applications. Using asymmetrical H-bridge inverters, more voltage levels can be generated in output voltage with the same number of components as the symmetrical converters. The concept of cascading multilevel H-bridge cells is used to propose a fifteen-level cascade inverter using a four-level H-bridge symmetrical diode-clamped converter, cascaded with classical two-level Hbridge inverters. A DC voltage ratio of cells is presented to obtain maximum voltage levels on output voltage, with adjacent switching vectors between all possible voltage levels; this can minimize the switching losses. This structure can save five isolated DC sources and twelve switches in comparison to conventional cascade converters with series two-level H bridge inverters. To increase the quality in presented hybrid topology with minimum number of components, a new cascade inverter is verified by cascading an asymmetrical four-level H-bridge diode-clamped inverter. An inverter with nineteen-level performance was achieved. This synthesizes more voltage levels with lower voltage and current THD, rather than using a symmetrical diode-clamped inverter with the same configuration and equivalent number of power components. Two different predictive current control methods for the switching states selection are proposed to minimise either losses or THD of voltage in hybrid converters. High voltage spikes at switching time in experimental results and investigation of a diode-clamped inverter structure raised another problem associated with high-level high voltage multilevel converters. Power switching components with fast switching, combined with hard switched-converters, produce high di/dt during turn off time. Thus, stray inductance of interconnections becomes an important issue and raises overvoltage and EMI issues correlated to the number of components. Planar busbar is a good candidate to reduce interconnection inductance in high power inverters compared with cables. The effect of different transient current loops on busbar physical structure of the high-voltage highlevel diode-clamped converters is highlighted. Design considerations of proper planar busbar are also presented to optimise the overall design of diode-clamped converters.

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Bouarfa, Abdelkader. "Méthodes de commande par allocation de convertisseurs statiques polyphasés, multi-niveaux : de la modélisation à la mise en oeuvre temps-réel." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30261/document.

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Dans nos travaux, nous nous intéressons à la commande des convertisseurs statiques à grand nombre d'interrupteurs. Le développement des topologies multi-niveaux multi-bras a ouvert l'accès aux domaines de la forte puissance et de la haute qualité harmonique. Outre cette montée en puissance, la commande spéciale de ces dispositifs permet de conférer au convertisseur des fonctionnalités avancées de plus en plus nécessaires, comme la possibilité de filtrage actif des harmoniques, la tolérance aux pannes, la gestion du réactif, les liaisons HVDC, etc. Toutefois, un plus grand nombre d'interrupteurs au sein d'une même structure de conversion se traduit par une forte croissance du nombre de variables de commande, des degrés de liberté et par une explosion combinatoire du nombre de configurations possibles. La synthèse de lois de commande suivant les approches traditionnellement conçues pour les topologies classiques, comme les méthodes de modulation vectorielle fondées sur la représentation géométrique du convertisseur, en devient rapidement fastidieuse pour les nouvelles topologies plus complexes. De plus, les interrupteurs présents en surnombre apportent des redondances fortes qui ne sont pas nécessairement exploitées, ou du moins arbitrairement. Nous proposons une nouvelle approche de commande qui se veut moins dépendante du nombre d'interrupteurs, et qui s'affranchit des limitations induites par les méthodes de modulation géométrique. Notre approche consiste dans un premier temps à formuler de manière algébrique des problèmes de commande qui sont généralement sous-déterminés, témoignant de la présence de redondances ou degrés de liberté, et contraints, car tenant compte des limitations propres aux rapports cycliques. De manière intéressante, ces problèmes offrent une similarité avec les problèmes dits d'allocation de commande rencontrés en aéronautique, en marine ou en robotique. Dans un second temps, dans le but de fournir à chaque période de découpage une solution de commande unique et optimisée, nous concevons de nouvelles méthodes d'allocation pour les convertisseurs statiques fondées sur l'optimisation numérique en ligne à partir de techniques d'optimisation linéaire. En conséquence, les rapports cycliques sont automatiquement optimisés pour satisfaire aux références de tension tout en respectant les saturations et en exploitant les redondances disponibles selon l'état actuel du convertisseur. Nous mettons en lumière les propriétés naturellement offertes par nos méthodes. Notamment, toutes nos solutions de modulation étendent de manière maximale la zone de linéarité du convertisseur. Nous proposons des méthodes d'allocation pour la commande en tension ou en courant de topologies variées : l'onduleur quatre bras deux niveaux, l'onduleur multicellulaire à condensateurs flottants, l'onduleur modulaire multi-niveaux. Concernant les convertisseurs multicellulaires, nos méthodes d'allocation utilisent automatiquement les degrés de liberté disponible pour fournir un équilibrage actif très rapide des tensions de condensateurs flottants. Aussi, grâce à la formulation algébrique des contraintes de commande, nos algorithmes peuvent prendre en compte un défaut sur un interrupteur pour conférer au convertisseur une propriété de tolérance aux fautes du point de vue de la commande
In our works, we are interested in control of high-switch-count power converters. The development of multileg, multilevel converters has opened the access to high power and high harmonic quality. The special control of these devices brings to the converter advanced abilities that are more and more requested nowadays, like active harmonic filtering, fault tolerance, active and reactive power transfer, High Voltage Direct Current (HVDC) links, etc. However, a higher number of switches in a conversion structure leads to a higher number of control variables, as well as more redundancies and a combinatorial explosion of the number of possible configurations. The development of control laws resulting from approaches traditionally designed for classical topologies, as for space vector modulation methods, becomes harder for new, much complex topologies. Moreover, the too many available switches bring strong control redundancies that are not necessarily exploited, at least arbitrarily. We propose a new control approach that is expected to be less dependent on the number of switches, and that does not suffer from limitations proper to geometrical modulation methods. Firstly, our approach consists in the algebraic formulation of control problems that are generally under-determined, highlighting the presence of redundancies and degrees of freedom, and constrained, because control limitations are taken into account. Interestingly, a connection can be highlighted to the so-called control allocation problem in flight control, robotics, or marine applications. Secondly, in order to compute a unique and optimized control solution at each switching period, we develop new control allocation methods for power converters based on on-line numerical optimization using linear programming techniques. Consequently, duty cycles are automatically optimized to satisfy voltage references while respecting saturations and exploiting available redundancies depending on the state of the converter. We highlight the properties naturally offered by our methods. In particular, all modulation solutions yield a maximized extension of the linearity range of the converter. We propose control allocation methods for the voltage or current control of many topologies: the four-leg two-level inverter, the multicellular flying capacitor inverter, the modular multilevel inverter

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Silva, Leonardo de Araujo. "Sintese de indutancia negativa para aplicação serie em redes de energia eletrica." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260861.

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Orientador: Jose Antenor Pomilio
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: Nesta tese é introduzida uma nova estratégia de controle que permite a síntese de indutâncias negativas para realização da compensação série de linhas de transmissão. O método, que é baseado na estratégia SDR (Síntese Direta de Reatâncias), opera com realimentação de estados e requer a medição de variáveis locais. Em relação aos métodos tradicionais, usando capacitores, a compensação através de indutância negativa pode ter desempenho superior, pois é possível conseguir sistemas mais estáveis, sem risco de ressonâncias, e com desempenho dinâmico superior, o que permite a realização de outras funções desejáveis, tais como o amortecimento de oscilações eletromecânicas e a compensação de cintilação luminosa. Dada a elevada potência requerida pela aplicação, sugere-se a utilização do Conversor Multinível em Cascata Assimétrico, que apresenta alto rendimento e é capaz de produzir uma tensão de saída de baixo conteúdo harmônico. Para este conversor, foi introduzida uma estratégia de controle que permite uma implementação sem que sejam necessárias fontes CC. Sugere-se também um procedimento para escolha do capacitor de filtragem que permite uma redução da corrente no conversor para uma dada condição de operação. São apresentados alguns estudos sobre a estabilidade da compensação série com indutância negativa. Para a técnica de controle proposta, são realizados estudos de autovalores, que permitem verificar a robustez com variação de parâmetros. Através de simulações, verificasse a estabilidade com a presença de elementos não modelados na planta, como capacitâncias parasitas. Também são apresentados estudos sobre a estabilidade para um modelo de simulação da ressonância subsíncrona, que considera o modelo do gerador e características mecânicas do eixo da turbina. Os resultados obtidos com estes estudos de estabilidade, bem com os resultados experimentais, indicam que a técnica proposta é viável para a aplicação
Abstract: This thesis introduces a new control strategy of realizing negative inductances with static converters for series compensation of transmission lines. The proposed method, which is basedon DRS (Direct Reactance Synthesis) technique, requires state feedback of variables that can be measured locally. The use of negative inductances instead of capacitors may yield performance improvement because there is no risk of resonance and it is possible to obtain higher stability margins and better dynamic performance. Consequently, it is possible to realize some useful functions that are not possible with conventional strategies, just as flicker ompensation and smoothing of electromechanical oscillations. Series compensation requires high power static converters and, due to this, the use of the Asymmetrical Cascaded Multilevel Converters (ACMC) is suggested. This high efficiency power converter is capable of producing a low THD output voltage using less power switches than other topologies. This thesis also introduces a DC control strategy for ACMC, which may allow negative inductance implementation with no DC sources. It is also suggested a design procedure for choosing the filter capacitance that reduces the required current capability of the power converter. Some studies regarding the stability of series compensation with negative inductances were carried on. For the new control strategy, it was possible to perform the eigenvalues analysis, that proved therobustness under some parameters variations. The stability considering elements that were not modeled, just as stray capacitances or generator and turbine shaft, were tested through simulations. The simulations and experimental results corroborate to prove that the control strategy is suitable for this application
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica

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Nicolás, Apruzzese Joan. "Design and analysis of a novel multilevel active-clamped power-converter." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/134933.

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Multilevel converter technology has been receiving increasing attention during the last years due to its important advantages compared to conventional two-level conversion. Multilevel converters reduce the voltage across each semiconductor. These converters also synthesize waveforms with better harmonic spectrum, and in most cases, increasing the efficiency of the power conversion system. However, a larger quantity of semiconductors is needed and the modulation strategy to control them becomes more complex. There are three basic multilevel converter topologies: diode clamped, flying capacitor, and cascaded H-bridge with separate dc sources. Numerous hybrid configurations combining them and other multilevel topologies have also been presented in the literature. A novel multilevel active-clamped (MAC) topology is the subject of study of the present thesis. This topology is derived from the generalized multilevel topology by simply removing all flying capacitors. The topology can also be seen as an extension into an arbitrary number of levels of the three-level active neutral-point-clamped (ANPC) topology. The novel converter is controlled using a proper set of switching states and a switching state transition strategy, which permits to obtain the maximum benefits from the converter. In this thesis, the performance and operating capabilities of the MAC topology are studied through comprehensive efficiency and fault-tolerance analyses. The efficiency analysis comprises a study of power-device conduction and switching losses in the topology, followed by analytical and experimental efficiency comparisons between the MAC converter and conventional two-level converters. In the analysis of the fault-tolerance capacity of the MAC topology both open- and short-circuit faults are considered and the analysis is carried out under single-device and two-simultaneous-device faults. Switching strategies to overcome the limitations caused by faults and topology variations to increment the fault-tolerance ability of the MAC converter are proposed. The thesis also proposes guidelines to guarantee a proper MAC converter design and improve its performance.

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Williams, Richard. "The use of multilevel power converter technology in aerospace starter-generator systems." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/3816/.

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This thesis investigates how a back-to-back connected, 5-level, diode-clamped multilevel inverter may be applied in an aerospace Starter / Generator (S/G) system. The performance of the proposed system is investigated with both wound field (WF) and permanent magnet (PM) synchronous machines. Control techniques are investigated to improve the waveform quality at the machine side. Also the grid interfacing of the converter is considered to make the system more resilient to AC distribution bus distortion. Aerospace generators are typically low inductance machines owing to the need to regulate the back-emf at the high rated speed, reduce stator losses and to increase power density. However, the driving of low inductance synchronous machines with a two level inverter results in a high level of current ripple at the same frequency as the converter switching frequency. A high level of current ripple increases losses in both the converter and machine necessitating additional heatsinking/cooling. The high ripple also results in increased radiated and conducted EMI. Additional filtering/shielding is therefore required to protect other vulnerable systems in the vicinity. The stability of the converter's controller may be adversely affected by a high level of current ripple. This instability can lead to the increased production of low order harmonic in the current waveform. The effect of interfacing a two-level inverter to an aircraft's AC distribution bus must also be considered. Power quality standards require the converter to draw a high quality sinusoidal current from the grid and introduce minimal distortion onto the voltage waveform. In order to reduce the current ripple in the machine windings and to ensure the distortion at the grid connection is within the governed limit, it is customary to use increased passive filtering and/or raise the converter switching frequency. Both of which incur a weight penalty. This study sought to investigate how a multilevel converter may be used as an alternative approach to this problem. The stepped PWM waveform produced by a multilevel converter offers superior harmonic performance and may therefore require reduced amounts of passive filtering whilst still producing a high quality waveform. The performance of the converter is initially demonstrated experimentally upon a PMSM. This is considered relevant as future 'embedded' S/Gs are likely to be PMSM due to the robust rotor structure and high power density. Performance is verified experimentally using a dynamometer test rig. The dynamometer is controlled to provide a rudimentary model of a gas turbine in both starting and generating mode. It is therefore possible to load the S/G in a similar manner to a real world application and provide realistic testing data. The converter is then applied to a WFSM. WFSMs are the industry norm for aerospace generators and it is this machine topology that is used as the S/G in Trent 1000 engine. Converter performance with a WFSM must therefore be assessed if this study is to be considered relevant. The excitation of the machine is investigated to ensure that the machine may be driven in motoring mode from zero speed and to maximise the available torque throughout the starting sequence. The excitation is then used to regulate the back-emf during generating mode. The same dynamometer test rig is used to provide full system test experimental data. Predictive control is then investigated to obtain a further reduction in waveform distortion in the stator current. Predictive control utilises a mathematical model of the load to predict the converter output voltage required in the next PWM period to minimise the current error. The estimated switching vector may then be applied in the next modulation period. This is shown to provide a substantial reduction in THD throughout both modes of operation. A reduction in THD in a real-world application would provide lower losses in both the machine and converter. The heatsinking/cooling arrangement may be reduced giving a possible weight reduction. In the final stage of this study, the control and synchronisation of the grid connected inverter is investigated. Aerospace power converters are required by the standards to function under distorted grid conditions. In this study a review is conducted into the competing grid synchronisation methods, to determine which is the most suitable to accommodate the heavily unbalanced grid waveforms commonly found on an aircraft distribution bus. A virtual-flux estimator is identified as the most promising technique as it eliminates the three voltage transducers at the grid connection. This not only makes the converter more resilient to grid distortion but may also increase the converter's reliability as three essential components have been removed. The system is assessed in both simulation and hardware. The level of grid distortion applied to the grid waveform is the maximum permissible according to the aerospace power quality standards. The system performance is satisfactory, maintaining synchronisation with the grid with minimal error despite the heavily unbalanced supply.

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Gebreel, Abd Almula G. M. "POWER CONVERSION FOR UHVDC TO UHVAC BASED ON USING MODULAR MULTILEVEL CONVERTER." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429358686.

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Espinoza, Bolaños Mauricio Antonio. "Control systems for high-power medium-voltage modular multilevel converter-based drives." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/168418.

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Doctor en Ingeniería Eléctrica
Hoy en día, la construcción de maquinaria y plantas industriales exigen soluciones de accionamiento con un diseño flexible y escalable. En sectores industriales como la petroquímica, la minería, la generación de energía, etc., existe una demanda de soluciones con alta eficiencia, seguridad integrada y respaldo de las compañías proveedoras. En este contexto, el Convertidor Multinivel Modular (MMC) ha aparecido como una opción prometedora para accionamientos de media tensión de alta potencia debido a sus características, como modularidad total, flexibilidad de control, niveles de media tensión, calidad de potencia y posible operación sin transformador. Por lo tanto, esta tesis discute la aplicación del MMC para accionamientos de máquinas. El modelado del MMC y sus sistemas de control asociados para esta aplicación son analizados ampliamente en este documento. Específicamente, se ha propuesto un nuevo modelado basado en coordenadas dq y su sistema correspondiente sistema de control para regular el valor instantáneo de las tensiones de los condensadores del MMC. Además, se ha propuesto la integración de los sistemas de control de la máquina y del MMC para mejorar el rendimiento general del sistema. Por ejemplo, se demostró que las corrientes circulantes requeridas durante bajas frecuencias ac se reducen al considerar la interacción de ambos sistemas de control. La efectividad de las estrategias de control propuestas se validó a través de extensos resultados experimentales, que se han publicado en dos artículos (IEEE Transactions on Industrial Electronics) y seis artículos de conferencia (indexados en la base de datos Scopus), así como contribuciones importantes en otros proyectos relacionados con el control de convertidores multinivel modulares. El prototipo utilizado se compone de 18 celdas de potencia. El sistema se controla utilizando un procesador de señales digitales y dos FPGAs. Un segundo MMC con 12 celdas de potencia también se usó para algunas pruebas, conformando una unidad Back-to-Back MMC. Se probó el rendimiento dinámico y en estado estable de las metodologías de control propuestas, considerando el arranque del MMC, cambios escalón tanto en el par y las corrientes de magnetización, rampas de velocidad, pruebas de cruce por velocidad cero, operación de rotor bloqueado, operación con flujo debilitado, diferentes condiciones de carga, manipulación de la tensión dc del MMC, etc. En todos los casos, el rendimiento alcanzado es consistente con los resultados esperados. Nowadays, machinery and plant construction are demanding drive solutions with flexible and scalable design. In industrial sectors such as petrochemical, mining, power generation, etc., there is a demand for solutions with high efficiency, integrated safety and support from the supplier companies. In this context, the Modular Multilevel Converter (MMC) has appeared as a promising option for high-power medium-voltage drives due to their characteristics, such as full modularity, control flexibility, medium-voltage levels, power quality and possible transformer-less operation. Thereby, this thesis discusses the application of the MMC as a machine drive. The modelling and control systems required for this application are extensively analysed and discussed in this document. Specifically, a novel dq-based modelling of the MMC and its associated control system has been proposed to regulate the instantaneous value of the MMC capacitor voltages. Additionally, the integration of the machine and MMC control systems has been proposed to enhance the performance of the overall system. For example, it was demonstrated that the required circulating currents during low-ac frequencies are reduced by considering the interaction of both control systems. The effectiveness of the proposed control strategies is validated through extensive experimental results, which have been published in two journal papers (IEEE Transaction on Industrial Electronics) and six conference papers (indexed in the Scopus database), as well as important contributions in other projects related to the control of modular multilevel converters. The downscaled prototype utilised is composed of 18 power cells. The system is controlled using a Digital Signal Processor and two Field Programmable Gate Arrays (FPGAs). A second MMC with 12 power cells was also used for some tests, conforming a Back-to-Back MMC-based drive. The dynamic and steady-state performance of the proposed control methodologies were tested, considering the MMC starting-up, step changes in both the torque and magnetising currents, speed-ramps, zero-speed crossing test, rotor-locked operation, flux-weakening operation, different loading conditions, manipulation of the input voltage of the MMC, etc. In all cases, the achieved performance is consistent with the expected results.

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Wu, Cong Martin. "Etude prospective de la topologie MMC et du packaging 3D pour la réalisation d’un variateur de vitesse en moyenne tension." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT027/document.

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La topologie modulaire multiniveaux est une structure d'électronique de puissance construite par la mise en série de sous-modules identiques, composés chacun d'une cellule de commutation et d'un condensateur. Un tel système de conversion pouvant comporter un grand nombre de cellules permet d'augmenter le rendement global et la qualité des signaux en sortie. De plus, il permet d'utiliser des composants basse tension présentant un meilleur comportement dynamique et un rapport qualité-prix bien supérieur aux composants moyenne tension. Il permet également, par rapport aux structures conventionnelles, une grande souplesse pour la conception et la fabrication du fait de son aspect modulaire, tout en s'affranchissant d'un transformateur volumineux et onéreux en entrée. Comparé aux autres types de topologies, avantageuses avec un nombre limité de niveaux, le convertisseur modulaire multiniveaux semble être mieux adapté aux applications en moyenne et haute tensions, qui sont tributaires de l'association des composants de puissance. Néanmoins, pour la variation de vitesse, un certain nombre de défis technologiques ont été mis en évidence, compte tenu du fonctionnement particulier de l'onduleur modulaire multiniveaux et des contraintes imposées par l'opération en très basse fréquence. En le fonctionnement normal, la forme d'onde des courants internes, contrairement aux autres types de topologies, n'est pas symétrique en raison de la distribution du courant direct dans chaque bras. Cela entraîne une disparité significative en termes de dissipation thermique parmi les interrupteurs constituant un sous-module. Avec le choix d'une technologie de packaging 3D, la possibilité de refroidir les puces semi-conductrices en double-face offre une meilleure capacité de refroidissement et une nouvelle perspective de conception des modules pour cette application. Un nouveau concept de report de puces est présenté et un prototype de tel module a été réalisé, modélisé et caractérisé. Il permet d'équilibrer globalement la chaleur dissipée par les puces sur les deux faces du module, problème inhérent à l'emploi de structure 3D. Conjugué à la mutualisation d'un interrupteur par deux puces en parallèle, la nouvelle architecture a aussi pour objectif d'équilibrer le refroidissement double-face dans le temps. En effet, pour les opérations en basse fréquence, les interrupteurs fonctionnent en régime instationnaire avec de forte variation de température, il n'est donc plus possible de compenser les effets thermomécaniques de chaque composant l'un par l'autre, comme en régime stationnaire et avec un positionnement planaire des puces. D'autre part, d'un point de vu systémique, la stratégie de commande et le dimensionnement des condensateurs flottants de l'onduleur modulaire multiniveaux sont deux aspects intimement liés. En effet, les condensateurs flottants sont le siège d'ondulations de tension de très forte amplitude. Cela a pour effet de déstabiliser l'onduleur, voire de provoquer la destruction des composants en atteignant des niveaux de tension trop élevés. Ainsi, des contrôleurs judicieusement conçus permettent de réduire les ondulations indésirables, et a fortiori, d'embarquer des capacités moins importantes dans le système, tant que ces dernières sont inversement proportionnelles à l'ondulation de la tension. Afin d'avoir une compréhension approfondie sur les dynamiques régissant le convertisseur modulaire multiniveaux, un modèle dynamique global basé sur la représentation d'état a été établi. Bien que cette représentation soit limitée à l'harmonique 2 des grandeurs caractéristiques, elle permet une fidèle interprétation du mécanisme de conversion sans passer par des modèles énergétiques bien plus complexes à exploiter, et de proposer des lois de commande montrant leur efficacité notamment autour de la fréquence nominale. Cela a été vérifié sur une maquette de puissance réalisée dans le cadre de cette thèse
Multilevel modular topology converts energy between two direct and alternative endings. This structure is constructed by the series connection of identical sub-modules, composed of a switching cell and a floating capacitor, and with arm inductors. Such a conversion system may reach a large number of levels increases the overall efficiency and quality of the output signals. In addition, it allows the use of low voltage components with better dynamics and cost effectiveness above the high voltage components. It also allows flexibility in the work of design and manufacture due to its modularity, while avoiding a bulky and expensive input transformer, regarding the conventional technology. Compared with other types of topologies, advantageous with a limited number of levels, the modular multilevel converter seems to be more suited for medium and high voltage applications, which are dependent on the association of power components. However, for variable speed drive application, a certain number of technological challenges have been highlighted, given the specific functional characteristics of the modular multilevel inverter and the constraints imposed by the very low frequency operation. On the one hand, for the normal operation of a multilevel modular converter, the waveform of the internal currents, in contrast to other types of topologies, is not symmetrical due to the distribution of the direct current in each phase leg. This may entail a significant disparity in terms of heat dissipation within the switching devices constituting a sub-module. Therefore, the problem of thermal management of active components is emphasized in the use of a modular multilevel converter. With the choice of a 3D packaging technology, interconnection by bumps, the ability to cool the semiconductor chips through the both sides of a module offers better cooling effects and a new perspective to design the power module for the studied structure. The concept of laying chips on both the two substrates of module without facing each other provides overall balanced dissipation in the space and permit to overcome the unbalanced heat distribution induced by bumps. Combined with the sharing of a switch by two chips in parallel, the proposal of the new architecture for 3D power module also aims to balance the double-sided cooling in the time range. Indeed, for the very low frequency operation, the switches operate in unsteady state where each switch has its own thermal behavior, it is no longer possible to compensate the thermo-mechanical constraints over each component with the help of the others, as in steady state and with a planar chips positioning scheme. On the other hand, from a systemic point of view, the control strategy and the dimensioning of floating capacitors of modular multilevel inverter are two interrelated aspects. Because the floating capacitors, having the role of energy sources, are loaded / unloaded through the modulation period, which causes very high voltage ripples across those capacitors with a very low frequency. This will destabilize the inverter and even provoke the destruction of components by approaching too high voltage levels. Thus, wisely designed controllers reduce unwanted ripples and, furthermore, allow embarking much smaller capacity in the system, as they are inversely proportional to the voltage ripple. In order to have a thorough understanding on the dynamics governing the modular multilevel converter, a comprehensive dynamic model based on state-space representation was established. Although this representation is limited to the second harmonic of characteristic variable, it allows a faithful interpretation of the conversion mechanism without using energy models, more complex to operate, and control laws can also be proposed and their effectiveness around the nominal frequency has been underlined. Concerning the very low frequency operations, another solution has been proposed and is ongoing patent pending

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Alepuz, Menéndez Salvador Simón. "Aportación al control del convertidor CC/CA de tres niveles." Doctoral thesis, Universitat Politècnica de Catalunya, 2004. http://hdl.handle.net/10803/6330.

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La presente tesis estudia, propone y realiza sus principales aportaciones en el campo del control para el convertidor CC/CA de tres niveles, sobre la topología denominada Neutral-Point-Clamped, aunque se puede extender a otras topologías y/o número de niveles. Se presenta una metodología de modelado que emplea funciones de conmutación de fase, el operador de promediado y la transformación D-Q, tal que los modelos obtenidos en el dominio D-Q contienen una información completa sobre la dinámica del sistema. La estrategia de conmutación se puede entender como una extensión de la estrategia PWM senoidal de dos a tres niveles. Esta estrategia es simple y no realiza el control de ninguna de las variables del sistema. En esta tesis, el controlador se encarga de regular todas las variables del sistema, incluido el equilibrio del bus de continua. Este es un enfoque diferente del convencional, donde el equilibrio del bus de continua se consigue mediante la elección adecuada de los estados redundantes del convertidor en la estrategia de conmutación, mientras que el resto de variables se regulan a través del controlador. Para la realización del controlador, se propone la técnica de control lineal multivariable LQR (Linear Quadratic Regulator), complementada con la técnica de control no lineal adaptativo denominada programación de ganancia (Gain Scheduling). Se presenta, además, una metodología de cálculo del controlador. Este control es versátil, abierto y adaptable. En cualquier caso, el controlador se puede adaptar a las necesidades concretas de cada aplicación. El cálculo del controlador se realiza mediante simulación con MatLab-Simulink. Los modelos matemáticos que emplean las funciones de conmutación del convertidor son aquellos que ofrecen un mejor compromiso entre velocidad de simulación y precisión. Para validar el control propuesto, se ha diseñado y construido un equipo experimental donde el controlador se ha mostrado aplicable, útil y eficaz en la regulación de las distintas cargas y aplicaciones experimentadas, incluso con carga no lineal, bajo diferentes condiciones de trabajo y variables a controlar, tanto en régimen permanente como en procesos transitorios. La rapidez y calidad de la respuesta transitoria es comparable a la de otros sistemas de control publicados. Es especialmente interesante el excelente control conseguido del equilibrio del bus de continua. Además, la robustez del control permite cancelar el error estacionario aunque diferentes parámetros del sistema presenten desviaciones significativas respecto los valores esperados. El uso de la programación de ganancia junto con la técnica LQR se ha mostrado muy efectivo, puesto que permite realizar diferentes tipos de control. Se ha comprobado la congruencia entre simulaciones y resultados experimentales obtenidos, lo que valida los modelos de simulación empleados y el proceso de diseño del controlador mediante simulación.
This dissertation study, propose and carry out the main contributions in the field of three-level inverter control, using the topology Neutral-Point-Clamped, although results can be extended to other topologies and/or number of levels. A procedure for modelling is presented, based on line-switching functions, moving average operator and D-Q transformation. Then, the obtained models in D-Q frame contain complete information about system dynamics. Switching strategy is simple and can be considered as an extension of two-level sinusoidal PWM to three level. The system variables are not controlled by the switching strategy. In this work, all the system variables are controlled by the regulator, including DC-link balance. This control approach is different than the conventional one, where DC-link balance is achieved by means of a proper selection of redundant states in the switching strategy, and the other variables are controlled by the regulator. The regulator is based on the multivariable linear control technique LQR (Linear Quadratic Regulator), in combination with the non-linear adaptive control technique Gain Scheduling. Moreover, a methodology for the calculation of the controller is presented. This controller is versatile, open and adaptable. However, the controller can be built depending on the concrete specifications of each application. The controller is calculated by means of simulation using MatLab-Simulink. The mathematical models based on the switching functions of the converter give the best trade-off between simulation speed and precision. In order to validate the proposed controller, an experimental prototype has been designed and implemented. Experimental results show that the controller is useful and effective for the regulation of different loads and applications, even with non-linear loads, different operation points and variables to control, in steady-state and transitory operation. Dynamic response speed and quality are similar to other control systems in the literature. The DC-link balance control achieved is specially interesting. Furthermore, steady-state error is cancelled due to the robustness of the controller, even though significant deviation of different system parameters are present. The use of Gain-Scheduling in combination with LQR is effective, allowing the calculation of regulators with different control strategies. Good agreement between simulations and experimental results has been found. This result validates simulation models and the design method for the controller, based on simulations.

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39

Alepuz, Menéndez Salvador Simón. "Aportació al control del convertidor CC/CA de tres nivells." Doctoral thesis, Universitat Politècnica de Catalunya, 2004. http://hdl.handle.net/10803/6330.

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La presente tesis estudia, propone y realiza sus principales aportaciones en el campo del control para el convertidor CC/CA de tres niveles, sobre la topología denominada Neutral-Point-Clamped, aunque se puede extender a otras topologías y/o número de niveles. Se presenta una metodología de modelado que emplea funciones de conmutación de fase, el operador de promediado y la transformación D-Q, tal que los modelos obtenidos en el dominio D-Q contienen una información completa sobre la dinámica del sistema. La estrategia de conmutación se puede entender como una extensión de la estrategia PWM senoidal de dos a tres niveles. Esta estrategia es simple y no realiza el control de ninguna de las variables del sistema. En esta tesis, el controlador se encarga de regular todas las variables del sistema, incluido el equilibrio del bus de continua. Este es un enfoque diferente del convencional, donde el equilibrio del bus de continua se consigue mediante la elección adecuada de los estados redundantes del convertidor en la estrategia de conmutación, mientras que el resto de variables se regulan a través del controlador. Para la realización del controlador, se propone la técnica de control lineal multivariable LQR (Linear Quadratic Regulator), complementada con la técnica de control no lineal adaptativo denominada programación de ganancia (Gain Scheduling). Se presenta, además, una metodología de cálculo del controlador. Este control es versátil, abierto y adaptable. En cualquier caso, el controlador se puede adaptar a las necesidades concretas de cada aplicación. El cálculo del controlador se realiza mediante simulación con MatLab-Simulink. Los modelos matemáticos que emplean las funciones de conmutación del convertidor son aquellos que ofrecen un mejor compromiso entre velocidad de simulación y precisión. Para validar el control propuesto, se ha diseñado y construido un equipo experimental donde el controlador se ha mostrado aplicable, útil y eficaz en la regulación de las distintas cargas y aplicaciones experimentadas, incluso con carga no lineal, bajo diferentes condiciones de trabajo y variables a controlar, tanto en régimen permanente como en procesos transitorios. La rapidez y calidad de la respuesta transitoria es comparable a la de otros sistemas de control publicados. Es especialmente interesante el excelente control conseguido del equilibrio del bus de continua. Además, la robustez del control permite cancelar el error estacionario aunque diferentes parámetros del sistema presenten desviaciones significativas respecto los valores esperados. El uso de la programación de ganancia junto con la técnica LQR se ha mostrado muy efectivo, puesto que permite realizar diferentes tipos de control. Se ha comprobado la congruencia entre simulaciones y resultados experimentales obtenidos, lo que valida los modelos de simulación empleados y el proceso de diseño del controlador mediante simulación.
This dissertation study, propose and carry out the main contributions in the field of three-level inverter control, using the topology Neutral-Point-Clamped, although results can be extended to other topologies and/or number of levels. A procedure for modelling is presented, based on line-switching functions, moving average operator and D-Q transformation. Then, the obtained models in D-Q frame contain complete information about system dynamics. Switching strategy is simple and can be considered as an extension of two-level sinusoidal PWM to three level. The system variables are not controlled by the switching strategy. In this work, all the system variables are controlled by the regulator, including DC-link balance. This control approach is different than the conventional one, where DC-link balance is achieved by means of a proper selection of redundant states in the switching strategy, and the other variables are controlled by the regulator. The regulator is based on the multivariable linear control technique LQR (Linear Quadratic Regulator), in combination with the non-linear adaptive control technique Gain Scheduling. Moreover, a methodology for the calculation of the controller is presented. This controller is versatile, open and adaptable. However, the controller can be built depending on the concrete specifications of each application. The controller is calculated by means of simulation using MatLab-Simulink. The mathematical models based on the switching functions of the converter give the best trade-off between simulation speed and precision. In order to validate the proposed controller, an experimental prototype has been designed and implemented. Experimental results show that the controller is useful and effective for the regulation of different loads and applications, even with non-linear loads, different operation points and variables to control, in steady-state and transitory operation. Dynamic response speed and quality are similar to other control systems in the literature. The DC-link balance control achieved is specially interesting. Furthermore, steady-state error is cancelled due to the robustness of the controller, even though significant deviation of different system parameters are present. The use of Gain-Scheduling in combination with LQR is effective, allowing the calculation of regulators with different control strategies. Good agreement between simulations and experimental results has been found. This result validates simulation models and the design method for the controller, based on simulations.

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Ghennam, Tarak. "Supervision d’une ferme éolienne pour son intégration dans la gestion d’un réseau électrique, Apports des convertisseurs multi niveaux au réglage des éoliennes à base de machine asynchrone à double alimentation." Thesis, Ecole centrale de Lille, 2011. http://www.theses.fr/2011ECLI0012/document.

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La première thématique développée dans ce mémoire vise à développer de nouveaux algorithmes pour la commande des éoliennes reposant sur une machine asynchrone à double alimentation et des convertisseurs multi niveaux. Deux stratégies de contrôle direct du courant, basées sur l’Hystérésis à Zones Carrées et l’Hystérésis à Zones Circulaires (HZCi) ont été proposées. Celles-ci consistent à appliquer des vecteurs de tension appropriés pour contrôler les puissances actives et réactive générées et permettent également d’équilibrer les tensions du bus continu interne des convertisseurs. Des résultats de simulation et d’expérimentation montrent que la stratégie basée sur l’HZCi est meilleure en termes de forme d’onde et de contenu harmonique des tensions de sortie.La seconde concerne la supervision et la gestion des puissances active et réactive dans une ferme éolienne au vu de son intégration dans un réseau électrique. Cette supervision centralisée est assurée par un algorithme qui distribue les consignes de puissance aux éoliennes de la ferme de manière proportionnelle. Ces références sont fonction de la capacité maximale de production de l’éolienne. Pour cela, une analyse des transits de puissance dans le système éolien à base de la machine asynchrone à double alimentation a été effectuée. Elle a permis de déterminer la caractéristique (P, Q) du générateur et de calculer ses limites de compensation en termes de puissance réactive. Une gestion locale des puissances de chaque éolienne a été développée permettant ainsi une répartition des puissances entre le stator de la machine et le convertisseur coté réseau en considérant plusieurs modes de fonctionnement du système éolien
This research work deals with two topics conditioning the large scale development of wind turbines into electrical grids. The first is devoted to the development of new algorithms for the control of Doubly Fed Induction Machine (DFIM) based wind energy conversion systems. Two direct current control strategies have been proposed and are based on the hysteresis square areas (HZCA) and hysteresis circular areas (HZCI). Both strategies apply an appropriate voltage vector to control the active and reactive powers delivered to the grid, and also, to balance the voltages of the inner DC bus converter. Simulation and experimental results show that the HZCI strategy is better than HZCA in terms of output voltage waveforms and harmonic contain.The second topic is dedicated to the active and reactive powers supervision in a wind farm in order to supply prescribed power references from the grid operator. This supervision is ensured by a centralized algorithm that distributes power references between wind turbines in a proportional way. These references are calculated according to the maximum production capacity of wind turbines. An analysis of the power flow in the DFIM based wind energy system has been made to identify the (P, Q) characteristic and to calculate limits in terms of reactive power compensation. The local power management of each wind system has been developed allowing the powers distribution between the stator of the DFIM and the grid side converter by considering several operating modes of the wind generator

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Abdalla, Imadeddin Abdalla. "Integrated PV and multilevel converter system for maximum power generation under partial shading conditions." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/4603/.

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The emerging trend towards the harnessing of the electrical power from solar energy has increased the research effort in power electronics applications. To achieve the required voltage level, a number of photovoltaic PV sources (cells/modules) are connected in series. The major challenge here is to deal with the partial shading problem, where the series connected PV sources are exposed to different insolation. The generated current is limited by the current of the shaded PV sources unless those sources are bypassed by diodes, in which case the total DC voltage is reduced and the shaded sources do not contribute to the generated output power. A power electronics approach can be employed to overcome the problem, by enabling both shaded and non-shaded sources to generate their maximum power, thereby and delivering the total generated power to the load. Thus no shaded PV source is bypassed or degrades the power extraction from the other PV sources. This thesis investigates the PV partial shading problem of individual PV sources which are connected in series. After the review and evaluation of existing methods to overcome this problem, the thesis employs for the first time the multilevel DC-Link inverter to deal with the problem of partial shading by using a novel control algorithm called PV permutation algorithm. The thesis also develops a simplified generalized Integration PWM (IPWM) algorithm which can be used to control higher level inverters. An improved maximum power point algorithm “voltage-hold perturbation and observation (VH-P&O)”, which overcomes the major tracking limitations, is developed from the basic P&O algorithm. Experimental systems of five and seven level DC-link inverters with a DC-DC buck converter system have been implemented. The digital processing unit eZdspTM F28335 is used to control the PV systems in real time, and Matlab-Simulink Real Time Data Exchange (RTDX) is employed to display the extracted power and to control the system parameters via a designed Graphical User Interface (GUI) window. The simulation and experimental results showed that the series connected PV sources operate at their maximum power points under partial shading conditions without affecting each other.

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Khlid, Ben Hamad. "Fuel cell power conditioning multiphase converter for 1400 VDC megawatts stacks." Thesis, Cape Peninsula University of Technology, 2019. http://hdl.handle.net/20.500.11838/3042.

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Thesis (PhD (Electrical Engineering))--Cape Peninsula University of Technology, 2019
Energy systems based on fossil fuel have demonstrated their abilities to permit economic development. However, with the fast exhaustion of this energy source, the expansion of the world energy demand and concerns over global warming, new energy systems dependent on renewable and other sustainable energy are gaining more interests. It is a fact that future development in the energy sector is founded on the utilisation of renewable and sustainable energy sources. These energy sources can enable the world to meet the double targets of diminishing greenhouse gas emissions and ensuring reliable and cost-effective energy supply. Fuel cells are one of the advanced clean energy technologies to substitute power generation systems based on fossil fuel. They are viewed as reliable and efficient technologies to operate either tied or non-tied to the grid to power applications ranging from domestic, commercial to industrial. Multiple fuel cell stacks can be associated in series and parallel to obtain a fuel cell system with high power up to megawatts. The connection of megawatts fuel cell systems to a utility grid requires that the power condition unit serving as the interface between the fuel cell plant and the grid operates accordingly. Different power conditioning unit topologies can be adopted, this study considers a multilevel inverter. Multilevel inverters are getting more popularity and attractiveness as compared to conventional inverters in high voltage and high-power applications. These inverters are suitable for harmonic mitigation in high-power applications whereby switching devices are unable to function at high switching frequencies. For a given application, the choice of appropriate multilevel topology and its control scheme are not defined and depend on various engineering compromises, however, the most developed multilevel inverter topologies include the Diode Clamped, the Flying Capacitor and the Cascade Full Bridge inverters. On the other hand, a multilevel inverter can be either a three or a five, or a nine level, however, this research focuses on the three-level diode clamped inverters. The aim of this thesis is to model and control a three-level diode clamped inverter for the grid connection of a megawatt fuel cell stack. Besides the grid, the system consists of a 1.54 MW operating at 1400 V DC proton exchange membrane fuel cell stack, a 1.26 MW three-level diode clamped inverter with a nominal voltage of 600 V and an LCL filter which is designed to reduce harmonics and meet the standards such as IEEE 519 and IEC 61000-3-6. The inverter control scheme comprises voltage and current regulators to provide a good power factor and satisfy synchronisation requirements with the grid. The frequency and phase are synchronised with those of the grid through a phase locked loop. The modelling and simulation are performed using Matlab/Simulink. The results show good performance of the developed system with a low total harmonic distortion of about 0.35% for the voltage and 0.19% for the current.

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Shehada, Ahmed. "Novel Multilevel Converter for Variable-Speed Medium Voltage Switched Reluctance Motor Drives." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85111.

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A novel multilevel converter that is especially suited for high speed multi-megawatt switched reluctance motor drives operating at the medium voltage level is presented. The drive is capable of variable speed, four-quadrant operation. Each phase leg of the converter contains an arbitrary number of cascaded cells connected in series with the phase winding. Each cell contains a half-bridge chopper connected to a capacitor. The converter is named the cascaded chopper cell converter. The modular nature of the converter with the ability to add redundant cells makes it very reliable, which is a key requirement for medium voltage drive applications. A comprehensive control algorithm that overcomes the challenges of balancing and controlling cell capacitor voltages is also proposed. A suitable startup algorithm to limit startup current and switching losses, as well as ensure that cell capacitor voltages remain controlled at startup, is suggested. Details of the drive design such as component sizing and control parameter selection are also discussed. A detailed simulation model is developed and explained, and simulation results are provided for primary validation. Operation with standard current and speed control is first simulated. Then a scheme that gives way to a controller that operates the drive in single-pulse mode is developed and presented. This single-pulse control scheme controls the turn-on and turn-off angles, as well as the energization voltage level, in order to obtain high efficiency. Practical considerations related to the drive such as reliability, efficiency, and cost considerations are also discussed. Finally, a detailed comparison of the proposed converter to another competing converter is performed. Besides its scalability to high voltages and powers, the reliability and efficiency of the proposed converter makes it also a candidate for sub-megawatt applications requiring minimum downtime, or any application where high efficiency or improved performance is required. A small part of this work is also dedicated to brushless dc machines. Control methods for a new converter for brushless dc machines are proposed and verified via simulation. The main advantage of this converter with the proposed control is that it allows exact control of torque or speed up to twice the rated speed, without resorting to current phase advancing or other flux-weakening techniques.
Ph. D.

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Leredde, Alexandre. "Etude, commande et mise en œuvre de nouvelles structures multiniveaux." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0094/document.

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Les structures de conversion multiniveaux permettent de convertir en moyenne tension et forte puissance. Celles-ci sont construites à partir de cellules de commutations et permettent d’augmenter le courant et la tension en entrée ou en sortie. Ces structures sont appelées multiniveaux car les formes d’ondes des tensions en sortie permettent d’avoir plus de deux niveaux de tension différents. Les différentes structures peuvent être classées dans différentes catégories tel que la mise en série de pont en H, les convertisseurs multicellulaires série ou parallèle ou encore les structures utilisant le fractionnement du bus continu. Toutes ces structures ont des propriétés et applications différentes, même si certaines structures ont des propriétés communes. Il est aussi possible de créer de nouvelles structures en mixant les différentes structures de bases des différentes familles de convertisseurs multiniveaux ou en assemblant les structures de base de la conversion statique. Même si l’utilisation de structure de conversion multiniveaux permet de convertir à forte puissance, celle-ci n’est pas toujours aisée. En effet l’augmentation du nombre de niveaux ou de la tension d’entrée implique également une augmentation du nombre de composants semiconducteurs. Ceci peut être un frein à l’utilisation de convertisseur multiniveaux. Pour cela une nouvelle structure utilisant des composants partagés entre les différentes phases est proposée afin de limiter leur nombre. Un autre problème important lié aux convertisseurs multiniveaux est l’équilibrage des tensions des condensateurs du bus continu si celui-ci est composé de plus de deux condensateurs mis en série. Pour cela plusieurs solutions sont possibles : soit en utilisant une commande spécifique utilisant la modulation vectorielle, soit en utilisant des structures auxiliaires qui ont pour but d’équilibrer les différentes tensions des condensateurs. Dans une dernière partie ont été proposées de nouvelles structures qui permettent à la fois d’augmenter le courant de sortie et la tension en entrée en utilisant les principes des structures de base des convertisseurs multicellulaires série et parallèle. De plus, ces structures ont des propriétés intéressantes sur les formes d’ondes de sortie. De ces structures a été conçu un prototype permettant de valider les résultats de simulation. Une commande numérique implantée sur FPGA a été réalisée et a permis d’avoir des résultats expérimentaux intéressants
This PhD Thesis deals with the study of new multilevel structures. At the beginning of this work, a new methodology to create new multilevel structures has been conceived. To evaluate the performances of these structures, there are many possibilities: number of output voltage levels, number of components, and the quality of the converters’ output waveforms. The list of criteria is not exhaustive. One technique to obtain an output multilevel waveform is to split the DC link in several capacitors. There is a limitation since putting more than two capacitors in serial connection leads to an unbalancing of these voltage capacitors. Several solutions are possible to balance these voltages. The first one uses the control of the structure in a three phase application, using a space vector modulation and minimizing the energy stored in the DC link. The second solution consists in using auxiliary circuits, which realize an energy transfer between one capacitor to another through an inductor. The drawback of this method is the high number of components. This problem can be reduced sharing some components between the three phases of the converter. The third part of this study is related to multicell converters, structures with very interesting good properties. New converter structures mix serial and parallel multicell converters, to obtain a hybrid converter with similar performances to the two basic converters. An experimental prototype was built to validate the results of the PhD. The digital control of this hybrid structure was made with a FPGA where two DSP processors were implemented

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Johnson, Jalen Craig. "High Power Density GaN Based Boost Inverter and Resonant Modular Multilevel Boost Converter for Automotive Applications." Thesis, North Dakota State University, 2018. https://hdl.handle.net/10365/28778.

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With the rise in demand for electric vehicles increasing, the need for high efficiency electrification systems is in high demand. One challenge is keeping full output power to the electric drives as the vehicle battery drops. This thesis presents a GaN based three-phase semi-quasi-z-source boost inverter that can produce twice the output voltage of a traditional inverter without the need for a boost converter stage. This single stage approach is great when the AC output voltage is relatively low. A second approach presented in this paper is a novel GaN based composite boost converter topology which is made up of a very efficient unregulated converter topology with an integrated partial power voltage regulation stage. This approach offers the benefits of very high efficiency from the unregulated converter stage and the regulated output voltage with the voltage regulation stage. This design can offer an estimated efficiency up to 98.6%.

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Viatkin, Aleksandr. "Development of a Test Bench for Multilevel Cascaded H-Bridge Converter with Self-Balancing Level Doubling Network." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14974/.

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This Master degree project was developed during an exchange program, established between the University of Bologna and the Technical University of Munich (TUM). The research activity was conducted at the Institute of Energy Conversion Technology (TUM department) in collobaration with Prof. Dr.-Ing. Hans-Georg Herzog and his research team. A symmetric 3-Phase Cascaded H-bridge Multilevel Inverter (CHBMLI), that is available in the TUM university laboratory, is reconfigured to operate as proposed using a Level Doubling Network (LDN). The LDN takes the form of a 3-phase half-bridge inverter that shares a common DC bus connected to a floating capacitor. This configuration allows almost to double number of output voltage levels. The LDN concept has inherent self-balancing capability that guarantees to maintain voltage across the LDN capacitor at nearly constant value and without any closed-loop control, while it does not consume or supply any power, apart from losses in the circuit. The proposed topology preserves the merit of CHBMLI modular structure, improving overall inverter’s reliability with reduced number of switching devices and required isolated DC sources compare with standard CHBMLI topology. Therefore, it significantly improves power quality, allows to reduce average device switching frequency, while minimizing cost and size of the power filter. Operation of the circuit is extensively verified by simulation in MATLAB/Simulink framework and experiments, performed on a grid-connected 3-phase five level laboratory prototype, specifically built as a part of the current Master Thesis. This work is a first step towards studying the proposed topology. Nevertheless, it provides a baseline for future analyses of the architecture and its possible variations.

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Du, Toit Daniel Josias. "Predictive control of a series-input, parallel-output, back-to-back, flying-capacitor multilevel converter." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/18087.

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Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2011.
ENGLISH ABSTRACT: This thesis investigates the viability of constructing a solid-state transformer (SST) with a series-input, parallel-output connection of full-bridge, three-level ying-capacitor converters. It focusses on the active recti er front-end of the SST which is used to control the input current to be sinusoidal and in-phase with the sinusoidal input voltage. A stack of two converters are built and tested. The input current, as well as the ying capacitor voltages of the two active recti ers in the stack, are actively controlled by a nite-state model-based predictive (FS-MPC) controller. The use of multiple ying-capacitor converters poses a problem when using FS-MPC because of the large number of possible switching states to include in the prediction equations. Three FS-MPC control algorithms are proposed to attempt to overcome the problem associated with the large number of switching states. They are implemented on an FPGA digital controller. The algorithms are compared on the bases of voltage and current errors, as well as their responses to disturbances that are introduced into the system. The simulation and experimental results that are presented shows that by interleaving the control actions for the two converters, one can obtain fast and robust responses of the controlled variables. The viability of extending the interleaving control algorithm beyond two converters is also motivated.
AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die moontlikheid van volbrug, drievlak vlieënde-kapasitoromsetters wat gebruik word om 'n serie-intree, parallel-uittree drywingselektroniese transformator (DET) te bou. Dit fokus op die aktiewe gelykrigter van die DET wat gebruik word om die intreestroom te beheer om sinusvormig en in fase met die sinusvormige intreespanning te wees. 'n Stapel van twee omsetters word gebou en getoets. Die intreestroom, sowel as die vlieënde kapasitorspannings van die twee aktiewe gelykrigters in die stapel, word aktief beheer met behulp van 'n eindige-toestand, model-gebaseerde voorspellende beheerder (ET-MVB). Die gebruik van veelvuldige vlieënde-kapasitoromsetters bemoeilik die implementering van 'n ET-MVB-beheerder as gevolg van die groot aantal skakeltoestande wat in die voorspellende vergelykings in ag geneem moet word. Drie ET-MVB-algoritmes word voorgestel om te poog om die probleme, wat met die groot aantal skakeltoestande geassosieer word, te oorkom. Die algoritmes word in 'n FPGA digitale verwerker geïmplementeer. Die algoritmes word vergelyk op grond van hul stroom- en spanningsfoute, asook hul reaksie op steurings wat op die stelsel ingevoer word. Die simulasie en praktiese resultate toon dat, deur die beheeraksies vir die twee omsetters te laat oorvleuel, die gedrag van die beheerde veranderlikes vinniger en meer robuust is. Die moontlikheid om die oorvleuelende beheeraksies uit te brei tot meer as twee omsetters word ook gemotiveer.

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Busquets, Monge Sergio. "A novel pulsewidth modulation for the comprehensive neutral-point voltage control in the three-level three-phase neutral-point-clamped dc-ac converte." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6372.

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Las topologías de convertidores multinivel han recibido una atención especial durante las dos últimas décadas debido a sus notables ventajas en aplicaciones de alta potencia y media/alta tensión. En estas topologías, y comparadas con el convertidor tradicional de dos niveles, el voltaje que soporta cada dispositivo semiconductor es menor, evitando los problemas asociados con la interconexión serie de dispositivos. La distorsión armónica en la tensión de salida es también menor y la eficiencia mayor. Pero incorporan un número superior de dispositivos semiconductores y la estrategia de modulación resultante es, por tanto, más compleja.
Entre estas topologías, el convertidor cc-ca de tres niveles trifásico con conexión al punto neutro del bus de cc es probablemente el más popular. La aplicación a este convertidor de técnicas de modulación convencionales causa una oscilación de la tensión del punto neutro de baja frecuencia (tres veces la frecuencia fundamental de la tensión de salida). Esta oscilación, a su vez, supone un incremento del estrés de tensión de los dispositivos y provoca la aparición de armónicos de baja frecuencia en la tensión de salida.
Esta tesis presenta una nueva técnica de modulación del pulso de conducción de los dispositivos semiconductores para convertidores de tres niveles trifásicos con conexión a punto neutro, capaz de conseguir un control completo de la tensión del punto neutro con una distorsión armónica reducida en la tensión de salida alrededor de la frecuencia de conmutación. Esta nueva técnica de modulación, basada en la definición de unos vectores espaciales virtuales, garantiza el equilibrado de la tensión del punto neutro con cualquier carga (lineal o no, cualquier factor de potencia) y para todo el rango de tensión de salida, con el único requisito de que la suma de corrientes de fase sea nula.
Las características de la técnica de modulación propuesta y sus beneficios con respecto a otras modulaciones se han verificado a través de simulaciones y experimentos tanto en lazo abierto como en lazo cerrado.
Multilevel converter topologies have received special attention during the last two decades due to their significant advantages in high-power medium- and high-voltage applications. In these topologies, and compared to the previous two-level case, the voltage across each semiconductor is reduced, avoiding the problems of the series interconnection of devices. The harmonic distortion of the output voltage is also diminished and the converter efficiency increases. But a larger number of semiconductors is needed and the modulation strategy to control them becomes more complex.
Among these topologies, the three-level three-phase neutral-point-clamped voltage source inverter is probably the most popular. The application of traditional modulation techniques to this converter causes a low frequency (three times the fundamental frequency of the output voltage) oscillation of the neutral-point voltage. This, in turn, increases the voltage stress on the devices and generates low-order harmonics in the output voltage.
This thesis presents a novel pulsewidth modulation for the three-level three-phase neutral-point-clamped converter, able to achieve a complete control of the neutral-point voltage while also having a low output voltage distortion at around the switching frequency. The new modulation, based on a virtual space vector concept, guarantees the balancing of the neutral-point voltage for any load (linear or nonlinear, any load power factor) over the full range of converter output voltage, the only requirement being that the addition of the output three-phase currents equals zero.
The performance of this modulation approach and its benefits over other previously proposed solutions are verified through simulation and experiments in both open- and closed-loop converter configurations.

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Smailes, Michael Edward. "Hybrid HVDC transformer for multi-terminal networks." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31173.

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There is a trend for offshore wind farms to move further from the point of common coupling to access higher and more consistent wind speeds to reduce the levelised cost of energy. To accommodate these rising transmission distances, High Voltage Direct Current (HVDC) transmission has become increasingly popular. However, existing HVDC wind farm topologies and converter systems are ill suited to the demands of offshore operation. The HVDC and AC substations have been shown to contribute to more than 20% of the capital cost of the wind farm and provide a single point of failure. Therefore, many wind farms have experienced significant delays in construction and commissioning, or been brought off line until faults could be repaired. What is more, around 75% of the cost of the HVDC and AC substations can be attributed to structural and installation costs. Learning from earlier experiences, industry is now beginning to investigate the potential of a modular approach. In place of a single large converter, several converters are connected in series, reducing substation individual size and complexity. While such options somewhat reduce the capital costs, further reductions are possible through elimination of the offshore substations altogether. This thesis concerns the design and evaluation the Hybrid HVDC Transformer, a high power, high voltage, DC transformer. This forms part of the platform-less (i.e. without substations) offshore DC power collection and distribution concept first introduced by the Offshore Renewable Energy Catapult. By operating in the medium frequency range the proposed Hybrid HVDC Transformer can be located within each turbine’s nacelle or tower and remove the need for expensive offshore AC and DC substations. While solid state, non-isolating DC-DC transformers have been proposed in the literature, they are incapable of achieving the step up ratios required for the Hybrid HVDC transformer [1]– [3]. A magnetic transformer is therefore required, although medium frequency and non-sinusoidal operation does complicate the design somewhat. For example, inter-winding capacitances are more significant and core losses are increased due to the added harmonics injected by the primary and secondary converters [1], [2]. To mitigate the impact of these complications, an investigation into the optimal design was conducted, including all power converter topologies, core shapes and winding configurations. The modular multilevel converter in this case proved to be the most efficient and practical topology however, the number of voltage levels that could be generated on the primary converter was limited by the DC bus voltage. To avoid the use of pulse width modulation and hence large switching losses, a novel MMC control algorithm is proposed to reduce the magnitude of the converter generated harmonics while maintaining a high efficiency. The development and analysis of this High Definition Modular Multilevel Control algorithm forms the bulk of this thesis’ contribution. While the High Definition Modular Multilevel Control algorithm was developed initially for the Hybrid HVDC Transformer, analysis shows it has several other potential applications particularly in medium and low voltage ranges.

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Jiang, Zhen. "Proposed Improvements to the Neutral Beam Injector Power Supply System." Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami150187797853065.

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Dissertations / Theses on the topic 'Multilevel Power Converters'

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