Tesis: "Ac generator"

1

Hu, Jiangang. "Sensorless control of AC machines for integrated starter generator application". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196258873.

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2

Yon, Jason M. "Variable frequency AC from a shunt regulated permanent magnet generator". Thesis, University of Bristol, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682723.

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The aviation industry is in the process of developing the All-Electric-Aircraft through a succession of increasingly More-Electric-Aircraft. Through this evolution, previously pneumatically or hydraulically powered functions are being implemented by electrical systems. This requires an increase in electrical power generation and distribution. To meet this increasing demand at competitive power densities, a change of generator technology may soon be required. Permanent Magnet (PM) machines, due to their power density, efficiency and simple robust construction, are a strong candidate technology for future aircraft electrical power generation. A variable frequency AC system based around a non-salient PM machine and a parallel shunt regulator is assessed and analysed to examine the effect of generator electromagnetic parameters on the rating of the regulator. With the correct pairing of PM machine and converter, it is anticipated that a system could be conceived which provides the necessary performance to meet the coming needs of the evolving aerospace industry at a competitive mass density. Key to achieving an optimised converter is the realisation of a machine with a specific PM flux linkage and inductance. Surface mounted PM machines offer a robust and simple machine construction. This topology is often employed where electromagnetic saliency is not required. However, their design is currently constrained by the effect of rotor containment structures on the machine's magnetic circuit. Alternative containment materials with a degree of magnetic permeability are calculated to reduce the effective air-gap usually presented by the containment material. Cold-rolled AISI 304L stainless steel exhibits such magnetic propelties. A prototype rotor is constructed incorporating a containment sleeve constructed of this material in a laminated construction. The machine is then tested to verify the analysis and to demonstrate shunt regulation of a PM generator. A further investigation is then conducted to assess the suitability of salient machine designs for operation as shunt regulated generators before conclusions are drawn and suggestions for future research are proposed.

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3

Coombe, H. Scott. "Development of a dynamic model of a mechanically driven polyphase AC generator /". This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03172010-020029/.

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4

Lopez, Santos Oswaldo. "Contribution to the DC-AC conversion in photovoltaic systems : Module oriented converters". Thesis, Toulouse, INSA, 2015. http://www.theses.fr/2015ISAT0001/document.

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Ces dernières années, un intérêt croissant pour les systèmes électroniques de puissance a été motivé par l'émergence de sources d'énergie distribuées et renouvelables raccordées aux réseaux électriques. Dans ce contexte, la nécessité de topologies de faibles puissances alimentées par quelques modules photovoltaïques, en évitant l'utilisation de transformateurs, a ouvert l'étude de convertisseurs spéciaux et l’étude des stratégies de commande associées afin d’assurer la stabilité, la fiabilité et un rendement élevé du dispositif. Une possible solution est d’utiliser un dispositif générique connu dans la littérature scientifique et commerciale comme « micro-onduleur » ou «convertisseur intégré au module » qui avec le module photovoltaïque définit un produit « plug and play » appelé "module AC".Ce travail est consacré à l'étude d'un micro-onduleur monophasé avec deux étapes sans transformateur raccordée au réseau. La topologie proposée est composé d’un convertisseur DC-DC non isolé élévateur avec un gain quadratique et un onduleur réducteur lié au réseau connectés en cascade. Le convertisseur DC-DC extrait en permanence la puissance maximale du module photovoltaïque malgré les changements dans les conditions environnementales. L'étape DC-AC injecte la puissance extraite par l'étape DC-DC dans le réseau et assure un niveau élevé de qualité de l’énergie. Les efforts de recherche de ce travail sont concentrés sur la mise au point de commandes utilisant comment base, la théorie de contrôle par mode de glissement, qui conduit à une mise en œuvre simple avec une description théorique complète validée á partir de simulations et expérimentations.Après avoir décrit l'état de l’art dans le premier chapitre, le manuscrit est divisé en quatre chapitres, qui sont dédiés respectivement à l’algorithme de recherche du point de puissance maximale (MPPT), á l’étape de conversion DC-DC, á l'étape de conversion DC-AC et finalement au micro-onduleur complet. Un nouvel algorithme de recherche extrémal du point de puissance maximale est développé (SM-ESC). Pour la étape DC-DC, le convertisseur élévateur quadratique avec seulement un interrupteur contrôlé est étudié utilisant le concept de résistance sans perte par mode de glissement (de l’acronyme anglais : Sliding-Mode Loss-Free-Resistor – SM-LFR) afin d’obtenir un gain de tension élevé avec un fonctionnement sûr et compatible avec l’algorithme MPPT. Pour la étape DC-AC, le convertisseur de pont complet est contrôlé comme un onduleur de source de puissance (de l’acronyme anglais : Power Source Inverter - PSI) en utilisant une commande par mode de glissement qui poursuit une référence sinusoïdale de courant de sortie. Cette commande est complétée par une boucle de régulation de la tension du bus DC qui assure une haute qualité d’énergie injectée dans le réseau. Enfin, les trois étapes constitutives sont fusionnées pour obtenir un micro-onduleur complètement contrôlé par la technique de mode de glissement, ce qui constitue le principal résultat et contribution de cette thèse
These last years, a growing interest in power electronic systems has been motivated by the emergence of distributed renewable energy resources and their interconnection with the grid. In this context, the need of low power topologies fed by a few photovoltaic modules avoiding the use of transformers opens the study of special converters and the associated control strategies ensuring stability, reliability and high efficiency. A resulted generic device known in the commercial and scientific literature as “microinverter” or “module integrated converter” performs a plug and play product together with the PV module called an “AC module”.This work is devoted to the study of a transformer-less single-phase double-stage grid-connected microinverter. The proposed topology has a non-isolated high-gain boost type DC-DC converter and a non-isolated buck type DC-AC converter connected in cascade through a DC bus. The DC-DC converter permanently extracts the maximum power of the PV module ensuring at the same time a good performance coping with power changes introduced by the change in the environmental conditions. The DC-AC stage injects the power extracted by the DC-DC stage into the grid ensuring a high level of power quality. The research efforts focus on the involved control functions based on the sliding mode control theory, which leads to a simple implementation with a comprehensive theoretical description validated through simulation and experimental results.After giving the state-of-the-art in the first chapter, the manuscript is divided into four chapters, which are dedicated to the Maximum Power Point Tracking (MPPT), the DC-DC stage and its control, the DC-AC stage and its control and the complete microinverter. A new Extremum Seeking Control (ESC) MPPT algorithm is proposed. The single-switch quadratic boost converter is studied operating as a Loss-Free-Resistor (LFR) obtaining a high DC output voltage level with a safe operation. The full-bridge converter is controlled as a Power Source Inverter (PSI) using a simple sliding-mode based tracking law, regulating the voltage of the DC bus and then ensuring a high power quality level in the grid connection. Finally, the three building blocks are merged to obtain a sliding mode controlled microinverter constituting the main result and contribution of the work

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5

Elmes, John. "MAXIMUM ENERGY HARVESTING CONTROL FOROSCILLATING ENERGY HARVESTING SYSTEMS". Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3400.

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This thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.
M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE

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6

Jarosz, Antoine. "Étude de la température et des vibrations des développantes d'alternateur hydraulique". Grenoble INPG, 1998. http://www.theses.fr/1998INPG0138.

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Ce mémoire concerne l'étude des contraintes mécaniques et thermiques que subit l'isolation statorique des alternateurs de centrale hydraulique. La zone plus particulièrement étudiée est la partie frontale des machines. Ainsi, dans le premier chapitre, il est rappelé la structure du bobinage statorique et l'ensemble des contraintes pouvant l'affecter. Cette première partie s'achève par une présentation des systèmes de maintenance prédictive et de leurs limites actuelles. Le deuxième chapitre concerne l'étude du comportement mécanique des développantes d'un alternateur hydraulique. La prise en compte de la non-homogénéité des matériaux par des modèles linéiques et volumiques ainsi que, la géométrie de cette structure sont décrites en détail-Ces modèles sont ensuite appliqués pour analyser qualitativement les déformées modales d'une seule développante puis, de l'ensemble du bobinage. Le troisième chapitre aborde la mesure expérimentale des températures et vibrations de trois alternateurs-moteurs utilisés dans des conditions usuelles de production d'énergie électrique. A partir de plusieurs enregistrements du régime permanent, il est clairement montré que l'isolation possède des propriétés viscoélastiques. Parallèlement, l'étude des régimes transitoires (démarrages et arrêts) nous indique que : * les efforts exercés sur les développantes sont principalement d'origine électromagnétique * l'utilisation du freinage électrique lors des phases d'arrêt peut exciter des modes propres de la machine et ainsi engendrer des niveaux vibratoires très élevés Le dernier chapitre présente un banc d'essai muHicontraintes capable de reproduire, sur un fragment de conducteur, les contraintes mécaniques, thermiques et électriques observées sur un alternateur. Les choix technologiques retenus sont justifiés et illustrés par plusieurs photographies. Enfin, une méthode analytique pour déduire le niveau des contraintes mécaniques dans l'isolation est proposée et validée expérimentalement
This thesis deals with thermal and mechanical stress that undergoes hydrogenerators stator insulation. More precisely, this study concems the stator endwinding zone. Thus, ail over the first chapter, stator winding structure and insulation stresses are described. This first part is concluded by a short présentation of on-line monitoring Systems and some pièces of information about their présent limits. The second chapter concems mechanical behavior of hydrogenerator endwindings. Materials non-homogeneity is taken account by three-dimensional and straight beam models moreover, endwinding geometry is described in détail. In the following step, thèse meihods are applied to analyse a single endwinding and the whole winding eigenforms. The third chapter contains a vibrations and température expérimental study of three generators-motors used in power generating units. Front the study of many steady-state recordings, insulation viscoelastic properties are proved. In the same way, mechanical transient analysis (starts and stops) shows that : * endwinding forces hâve mainly electromagnetic origins * the electrical braking during the stop séquences may lead to high vibration levels caused by machine naturel frequencies The last chapter purpose is to présent an expérimental testing bench able to repnoduce, on a short part of a generator bar, thermal, mechanical and high voltage stresses measured on real machines. Technological solutions chosen are justified and illustrated by many pictures. To conclude, an analytical method for predicting insulation mechanical stress level is proposed and compared with expérimental data

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7

Phan, Anh Minh. "Optimisation énergétique des groupes turbine-alternateur-convertisseur à vitesse variable". Grenoble INPG, 1998. http://www.theses.fr/1998INPG0031.

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La valorisation technico-economique des projets de centrales hydroelectriques depend des ressources hydrauliques disponibles et aussi des procedures d'exploitation utilisees en fonction de la puissance electrique demandee. Classiquement les groupes hydroelectriques sont exploites a vitesse de rotation constante, synchrone avec la frequence du reseau. Grace aux progres de l'electronique de puissance, il est maintenant possible d'utiliser des convertisseurs de frequences jusqu'a des puissances tres importantes et donc de faire fonctionner les turbines hydrauliques a vitesse variable. Ce nouveau degre de liberte permet d'obtenir un rendement du groupe turbine-alternateur-convertisseur le plus souvent superieur a l'ensemble turbine-alternateur a vitesse constante. Pour justifier l'installation d'un tel convertisseur, il est necessaire de verifier que le gain lie a la variation de vitesse compense le surcout correspondant. Dans ce memoire, on a developpe un modele global parametrique du fonctionnement du groupe turbine-alternateur-convertisseur. Le modele de la turbine est base sur la parametrisation des pertes a partir de mesures experimentales. L'alternateur est modelise a partir d'une structure theorique classique dont les coefficients sont obtenus par des essais sur prototype ou sur modele. Le convertisseur est represente par un modele sequentiel. Une procedure propose par l'auteur permet de trouver le reglage optimal de chaque element de l'ensemble complet compte tenu du potentiel hydraulique et de la demande de puissance electrique. Par simulation, il est alors possible de determiner le productible annuel de la centrale. Cette etude a ete testee et validee sur une installation experimentale de laboratoire equipee d'une turbine francis de 5 kw. Cette analyse a ensuite ete appliquee a un site reel presentant de grandes variations annuelles de chutes. Le productible annuel avec cette methode a ete compare a la simulation a frequence constante. Le gain energetique ainsi obtenu est un facteur important pour l'aide a la decision base des consideration technico-economique.

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8

Chen, Jianyi. "Performance enhancement of AC machines and permanent magnet generators for sustainable energy applications". Thesis, Curtin University, 1999. http://hdl.handle.net/20.500.11937/1663.

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Sustainable energy solutions are aimed to reduce the consumption of fossil fuels by using renewable energy sources and energy efficiency techniques. This thesis presents two new sustainable energy applications in the field of electrical machines.Polyphase induction motors dominate the energy usage spectrum for industrial and commercial applications. The conventional winding structure used in both synchronous and induction machines has a basic unit of the winding with a 60 degree phase belt and a three phase connection either in star or delta. A new winding structure using an innovative Star-Delta Series Connection (SDSC) which has a high winding coefficient and low harmonic content is presented in this thesis. The principle of the SDSC winding is described. The Electro-Magnetic Belt and Electro-Magnetic Space diagram are two important means to be used for optimization of the new winding. Experimental results from two prototypes confirm the theoretical analysis. The efficiency of the new machine at rated load increased by about 3.8% as compared to the standard machine with a conventional winding structure.Wind energy is one of the most attractive renewable energy options. Wind turbines are designed to couple either synchronous or asynchronous generators with various forms of direct or indirect connection with grid or diesel generators. Permanent magnet (PM) generators using high energy Neodymium- Iron-Boron magnets offer advantages such as direct coupling without gear box, absence of excitation winding and slip rings, light weight and smaller size. This thesis presents the design and development of an outer-rotor PM generator suitable for wind energy conversion. The initial electromagnetic design followed by a Finite Element Analysis is presented in detail. A 20 kW prototype machine was built and extensively tested. It was found that the machine could maintain an efficiency of about 85% for a wide operating range. Equivalent circuit models were developed. The results of the Finite Element analysis matches closely with the experimental and the designed values.

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9

Adabi, Firouzjaee Jafar. "Remediation strategies of shaft and common mode voltages in adjustable speed drive systems". Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/39293/1/Jafar_Adabi_Firouzjaeel_Thesis.pdf.

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AC motors are largely used in a wide range of modern systems, from household appliances to automated industry applications such as: ventilations systems, fans, pumps, conveyors and machine tool drives. Inverters are widely used in industrial and commercial applications due to the growing need for speed control in ASD systems. Fast switching transients and the common mode voltage, in interaction with parasitic capacitive couplings, may cause many unwanted problems in the ASD applications. These include shaft voltage and leakage currents. One of the inherent characteristics of Pulse Width Modulation (PWM) techniques is the generation of the common mode voltage, which is defined as the voltage between the electrical neutral of the inverter output and the ground. Shaft voltage can cause bearing currents when it exceeds the amount of breakdown voltage level of the thin lubricant film between the inner and outer rings of the bearing. This phenomenon is the main reason for early bearing failures. A rapid development in power switches technology has lead to a drastic decrement of switching rise and fall times. Because there is considerable capacitance between the stator windings and the frame, there can be a significant capacitive current (ground current escaping to earth through stray capacitors inside a motor) if the common mode voltage has high frequency components. This current leads to noises and Electromagnetic Interferences (EMI) issues in motor drive systems. These problems have been dealt with using a variety of methods which have been reported in the literature. However, cost and maintenance issues have prevented these methods from being widely accepted. Extra cost or rating of the inverter switches is usually the price to pay for such approaches. Thus, the determination of cost-effective techniques for shaft and common mode voltage reduction in ASD systems, with the focus on the first step of the design process, is the targeted scope of this thesis. An introduction to this research – including a description of the research problem, the literature review and an account of the research progress linking the research papers – is presented in Chapter 1. Electrical power generation from renewable energy sources, such as wind energy systems, has become a crucial issue because of environmental problems and a predicted future shortage of traditional energy sources. Thus, Chapter 2 focuses on the shaft voltage analysis of stator-fed induction generators (IG) and Doubly Fed Induction Generators DFIGs in wind turbine applications. This shaft voltage analysis includes: topologies, high frequency modelling, calculation and mitigation techniques. A back-to-back AC-DC-AC converter is investigated in terms of shaft voltage generation in a DFIG. Different topologies of LC filter placement are analysed in an effort to eliminate the shaft voltage. Different capacitive couplings exist in the motor/generator structure and any change in design parameters affects the capacitive couplings. Thus, an appropriate design for AC motors should lead to the smallest possible shaft voltage. Calculation of the shaft voltage based on different capacitive couplings, and an investigation of the effects of different design parameters are discussed in Chapter 3. This is achieved through 2-D and 3-D finite element simulation and experimental analysis. End-winding parameters of the motor are also effective factors in the calculation of the shaft voltage and have not been taken into account in previous reported studies. Calculation of the end-winding capacitances is rather complex because of the diversity of end winding shapes and the complexity of their geometry. A comprehensive analysis of these capacitances has been carried out with 3-D finite element simulations and experimental studies to determine their effective design parameters. These are documented in Chapter 4. Results of this analysis show that, by choosing appropriate design parameters, it is possible to decrease the shaft voltage and resultant bearing current in the primary stage of generator/motor design without using any additional active and passive filter-based techniques. The common mode voltage is defined by a switching pattern and, by using the appropriate pattern; the common mode voltage level can be controlled. Therefore, any PWM pattern which eliminates or minimizes the common mode voltage will be an effective shaft voltage reduction technique. Thus, common mode voltage reduction of a three-phase AC motor supplied with a single-phase diode rectifier is the focus of Chapter 5. The proposed strategy is mainly based on proper utilization of the zero vectors. Multilevel inverters are also used in ASD systems which have more voltage levels and switching states, and can provide more possibilities to reduce common mode voltage. A description of common mode voltage of multilevel inverters is investigated in Chapter 6. Chapter 7 investigates the elimination techniques of the shaft voltage in a DFIG based on the methods presented in the literature by the use of simulation results. However, it could be shown that every solution to reduce the shaft voltage in DFIG systems has its own characteristics, and these have to be taken into account in determining the most effective strategy. Calculation of the capacitive coupling and electric fields between the outer and inner races and the balls at different motor speeds in symmetrical and asymmetrical shaft and balls positions is discussed in Chapter 8. The analysis is carried out using finite element simulations to determine the conditions which will increase the probability of high rates of bearing failure due to current discharges through the balls and races.

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10

Chen, Jianyi. "Performance enhancement of AC machines and permanent magnet generators for sustainable energy applications". Curtin University of Technology, School of Electrical and Computer Engineering, 1999. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10442.

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Sustainable energy solutions are aimed to reduce the consumption of fossil fuels by using renewable energy sources and energy efficiency techniques. This thesis presents two new sustainable energy applications in the field of electrical machines.Polyphase induction motors dominate the energy usage spectrum for industrial and commercial applications. The conventional winding structure used in both synchronous and induction machines has a basic unit of the winding with a 60 degree phase belt and a three phase connection either in star or delta. A new winding structure using an innovative Star-Delta Series Connection (SDSC) which has a high winding coefficient and low harmonic content is presented in this thesis. The principle of the SDSC winding is described. The Electro-Magnetic Belt and Electro-Magnetic Space diagram are two important means to be used for optimization of the new winding. Experimental results from two prototypes confirm the theoretical analysis. The efficiency of the new machine at rated load increased by about 3.8% as compared to the standard machine with a conventional winding structure.Wind energy is one of the most attractive renewable energy options. Wind turbines are designed to couple either synchronous or asynchronous generators with various forms of direct or indirect connection with grid or diesel generators. Permanent magnet (PM) generators using high energy Neodymium- Iron-Boron magnets offer advantages such as direct coupling without gear box, absence of excitation winding and slip rings, light weight and smaller size. This thesis presents the design and development of an outer-rotor PM generator suitable for wind energy conversion. The initial electromagnetic design followed by a Finite Element Analysis is presented in detail. A 20 kW prototype machine was built and extensively tested. It was found that the machine could maintain an ++
efficiency of about 85% for a wide operating range. Equivalent circuit models were developed. The results of the Finite Element analysis matches closely with the experimental and the designed values.

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11

Stevens, Jonathan. "HVDC transmission and AC hubs for offshore wind generation". Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/87531/.

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The offshore AC hub was identified as a feasible network topology for an offshore node applied in a future pan-European Supergrid. A model of an offshore AC hub was developed in SimPowerSystemsTM using the round three offshore wind development zone Dogger Bank, as a case study. Two control philosophies, master-slave and droop control, are shown to successfully manage the voltage, current and complex power flow in the offshore AC hub following planned changes in operating conditions. The impacts of three different fault scenarios on the offshore AC hub are investigated. It is shown that each fault severely impedes normal operation of equipment in the offshore AC hub, as equipment ratings are exceeded. In addition, the loss of infeed to the onshore UK power network is extensive. Based on these outcomes, it is identified that additional fault management systems are required. A novel centralised fault management system is then developed based on an online OPF algorithm. The performance is compared to de-centralised fault management system, and advantages and disadvantages of the two methods are discussed. The centralised fault management system is implemented on a realtime platform as hardware-in-the-loop, with the offshore AC hub implemented on a Real Time Digital Simulator. The simulation and experimental results are then compared to confirm the validity of the simulation results.

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12

Duggan, Claire. "The generation of the amyloid precursor protein intracellular domain". Thesis, University of Manchester, 2005. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:77486.

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Alzheimer's disease (AD) is the most common cause of a progressive decline of cognitive function in aged humans. It is thought to be a result of the formation of amyloid plaques in the brain that are largely composed of β-amyloid (Aβ), which is one of the cleavage products of the amyloid precursor protein (APP). The amyloidogenic processing of APP to produce the Aβ peptides requires sequential proteolytic cleavages by the β- and γ-secretases. APP is first cleaved by the β-secretase to produce APP-C99, and this product is a substrate for further processing by the γ-secretase that cleaves within its transmembrane domain to produce N-terminal Aβ peptides and the C-terminal APP intracellular domain (AICD). On the basis of similarities to the Notch processing pathway, it has been postulated that the AICD may play a role in gene regulation following its release in response to some form of extracellular signal. In order to better understand the production and fate of the AICD, I have investigated the potential for exploiting a cell-free system to study its generation and properties. Having generated a number of model APP-derived fragments and shown them to be efficiently membrane integrated in vitro, I went on to study AICD production. I discovered that AICD-like fragments are extremely labile when synthesised in a rabbit reticulocyte lysate system and are rapidly degraded via a metalloproteinase, most likely the insulin degrading enzyme (IDE). The in vitro stability of these model AICD-like fragments was dependent upon the precise chain length of the polypeptide and N-terminal processing may preface the activity of IDE in vitro. The rapid degradation of the AICD in vitro is in close agreement with previous in vivo studies, and taken together such data are consistent with a role for the AICD in a signalling pathway of some form. A variety of approaches were also taken to try to generate the AICD by the γ-secretase mediated cleavage of the APP-C99 fragment, a biologically relevant substrate. In no case was any evidence of such cleavage observed in vitro and hence I conclude that the endoplasmic reticulum does not possess an active form of the γ-secretase. Preliminary in vivo-based studies did provide evidence for the γ-secretase cleavage of APP-C99 fragments, consistent with current models implying that such processing takes place at the cell surface and/or in endosomes and not at the endoplasmic reticulum.

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13

Robinson, James A. "Quasi Taylor cones generated by AC fields on water surfaces". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58229.pdf.

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14

Adrees, Atia. "Risk based assessment of subsynchronous resonance in AC/DC systems". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/risk-based-assessment-of-subsynchronous-resonance-in-acdc-systems(8750b478-51c8-4dd2-b54d-70cee13488ae).html.

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This thesis investigates the phenomenon of subsynchronous resonance (SSR) in meshed series compensated AC/DC systems in the presence of operational uncertainties. The main contribution of this research is the novel application of risk assessment methods to SSR studies. In terms of network topology, future electric power transmission networks alongside the current power networks are expected to be meshed, and consequently, exposed to relative low risk of subsynchronous resonance. However, power systems are increasingly operated closer to stability limits in order to enhance efficiency and economics of their use. These stressed operating conditions may contribute to the deterioration in the system reliability. Uncertainty associated with the loads will also further diversify in the future due to new type of devices connected to the network whilst the integration of stochastic renewable generation sources will add another layer of uncertainty to system operation. There is a growing necessity to explore the challenges created by the increased uncertainty in generation and loads, and quantify risk to keep a balance between avoiding potentially catastrophic systems failures and mitigating for extremely rare event. This research work introduces risk assessment in subsynchronous resonance studies. Two indices are developed to quantify the severity of dynamic instability and transient torque amplification. Using these indices generators in the network can be ranked based on potential exposure to SSR. Following the development of indices, a methodology is proposed to evaluate the risk of SSR. The developed methodology takes into account the severity of SSR problem and probabilities of different contingencies and different operating conditions of a turbine generator. A robust investigation, into the effect of uncertainties on both aspects of SSR with symmetrical and asymmetrical compensation schemes, is also performed. The results of the analysis reveal that a critically compensated system in normal meshed network configuration may become dynamically unstable with as low as ±5% uncertainty in mechanical parameters. The critical compensation level with asymmetrical compensation in normal network configuration and each contingency becomes higher. It is also shown that the risk level assessed with the developed methodology does not change under the influence of ±5% uncertainties in the mechanical parameters. After establishing, that risk, based approach provides a better picture of all credible scenarios and risk of SSR in compensated power network, a methodology based on risk evaluation of SSR for selecting an optimal combination of TCSCs and fixed series capacitors for compensation of transmission lines is presented. This proposed methodology maximizes the use of fixed capacitors whilst maintaining the risk of SSR within an acceptable level in all credible contingencies and operating conditions.

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15

Bensmaine, Fayçal. "Modélisation et commande d'un système de stockage d'énergie à base de supercondensateur pour l'hybridation des groupes électrogènes". Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2341.

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Les travaux de recherche dans ce mémoire s’inscrivent dans l'étude et la commande d'un nouveau concept du groupe électrogène hybride permettant de réduire la puissance du moteur diesel (downsizing) d’économiser du carburant et d’améliorer le comportement de la génératrice synchrone durant les régimes transitoires. La solution adoptée consiste à mettre en parallèle à la génératrice synchrone un système de stockage d'énergie. Ce système est composé d'un onduleur avec un supercondensateur du côté du bus continu. L’objectif de la thèse a été de dimensionner l’ensemble supercondensateur /convertisseur statique et de développer une commande ayant des performances optimales pour obtenir le meilleur compromis entre l’énergie échangée dans le supercondensateur et l’efficacité sur la vitesse du groupe et sur l’amplitude des tensions de l’alternateur. Une commande par retour d’état avec intégration de l’écart en utilisant l’approche LMIs a été mise en place pour la synthèse des régulateurs des boucles de courants de l'onduleur. Une deuxième commande a été développée pour réguler la tension variable aux bornes du supercondensateur. Un simulateur regroupant l’alternateur et le système de stockage a été développé pour la mise au point de ces commandes. Toutes les validations ont été faites sur une maquette expérimentale spécifiquement élaborée pour cette thèse. Les essais ont été menés avec un moteur d’entraînement électrique et sur un diesel. En conclusion, les essais expérimentaux ont mis en évidence l’apport important de cette hybridation sur les variations de vitesse du diesel et sur la tension aux bornes de l’alternateur lors d’important impact ou de délestage de la charge
The research in this thesis are part of study and control of a new concept of hybrid generator to reduce the power of the diesel engine (downsizing) in order to save fuel and improve the behavior of the synchronous generator during transients. The adopted solution is to place in parallel with the synchronous generator an energy storage system. The latter consists of an inverter with a super capacitor on the DC bus. The aim of the thesis was to scale the entire supercapacitor / static converter and to develop a control law having the best performance with the best compromise between the energy exchanged in the supercapacitor, efficiency, the group speed and voltage amplitude of the generator. A feedback control condition with integration of the deviation using LMI's approach has been established for the synthesis of loop current regulators from the inverter.A second control law was developed to regulate the variable voltage across the supercapacitor. A simulator combining generator and storage system has been developed to test these commands.All validations were made on an experimental test rig specifically developed for this thesis. The tests were conducted with an electric drive motor in the test platform of the LIAS and with a diesel in that of the Leroy Somer Motors company.Finally, experimental tests have highlighted the significant contribution of this hybridization on the diesel speed variationsand on the terminal voltage of the alternator during impact or load shedding

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16

Roets, Hendrik Adriaan. "Effect of altitude on audible noise generated by AC conductor corona". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71810.

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Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Power utilities are expected to keep the cost of electricity as low as possible. They are also expected to be environmentally friendly and, amongst other things, not to produce unacceptable audible noise. When the electric field on a conductor is high enough corona is produced and this is accompanied by audible noise. Air pressure, which is directly related to altitude, has an effect on the voltage at which corona will start. It is more difficult to ionise the air at sea level (high air pressure) than at high altitude (low air pressure). Altitude does not only affect the corona inception voltage, but also the intensity of the audible noise. A thorough scan of literature revealed that there is very little evidence of prior research work on the effect of air density on corona under fair weather (dry) conditions. In South Africa, transmission lines are built at altitudes higher than 1800 m above sea level. The cost of a 400 kV line is in the region of R2M per km. It is important to predict the noise levels under a proposed line accurately, before it is energised. This research indicated that the altitude correction for conductor corona audible noise, under dry conditions, might be steeper than the general accepted correction of 1 dB/300m. This correction, however, appears to be valid for heavy rain conditions. Under heavy rain conditions the corona is mainly determined by the water droplets, whereas under dry conditions the condition of the conductor plays the biggest role. The air density therefore has a bigger effect on the corona performance under dry conditions. The implication of a steeper altitude correction for dry conditions is that too low noise levels will be predicted for a higher altitude, which could lead to complaints. On the other hand, predictions for lower altitudes will be too conservative.
AFRIKAANSE OPSOMMING: Daar word van kragvoorsieners verwag om die koste van elektrisiteit so laag as moontlik te hou. Hulle is verder onder druk om omgewingsvriendelik te wees en om onder andere nie onaanvaarbare hoorbare geraas te veroorsaak nie. Wanneer die elektriese veld op ‘n geleier hoog genoeg is, kan korona ontstaan wat dan hoorbare geraas veroorsaak. Die lugdruk, en daarom die hoogte bo seevlak, beïnvloed die spanning waarby ‘n geleier in korona sal gaan. Dit is moeiliker om die lug te ioniseer by seevlak (hoë lugdruk) as hoog bo seevlak (lae lugdruk). Die hoogte bo seevlak beïnvloed daarom nie net die spanning waarby korona sal begin nie maar ook die intensiteit van die hoorbare geraas. Dit wil voorkom of die effek van hoogte bo seevlak, op hoorbare geraas, a.g.v. geleier korona tot op datum baie skraps nagevors is. Baie min kon in die literatuur gevind word op die effek onder droë toestande. In Suid-Afrika is dit nodig om transmissielyne op hoogtes van 1800 m en hoër te bou. So ‘n lyn (400 kV) kos in die omgewing van R2M per km. Dit is daarom van uiterste belang om die geraasvlakke wat ‘n beplande lyn sal veroorsaak, akkuraat te bepaal, voordat so ‘n lyn aangeskakel word. Hierdie navorsing het gewys dat die effek van hoogte bo seespieël op hoorbare korona geraas onder droë toestande groter kan wees as wat algemene aanvaar word. Die helling van die korreksiefaktor vir hoogte bo seevlak blyk steiler as 1 dB/300 m te wees vir droë toestande. Die implikasie hiervan is dat geraas voorspellings vir hoër hoogtes bo seespieël te laag sal wees en die vir lae hoogtes te konserwatief kan wees. Die navorsing stem egter saam met die korreksiefaktor van 1 dB/300 m onder swaar reën toestande. Dit wil voorkom of die invloed van die waterdruppels op geleier korona groter is as lugdruk. Onder droë toestande speel die toestand van die geleier 'n groter rol en is die effek van lugdruk groter.

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17

Gu, Patrick. "Advanced Nonlinear Control and Estimation Methods for AC Power Generation Systems". Thesis, Southern Illinois University at Edwardsville, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10263630.

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Due to the increased demand for reliable and resilient controls in advanced power generation systems, new control methods are required to tackle traditional problems within these systems. This work discusses a control method and an estimation method for advanced control systems. The control method is sliding mode controls of a higher order, which is used to control the nonlinear wind energy conversion system while lessening the chattering phenomena that causes mechanical wear when using first order sliding mode controls. The super-twisting algorithm is used to create a second order sliding mode control. The estimation method is the derivation of a Resilient Extended Kalman filter, which can estimate and control the system through sensor undergoing failures with a binomial distribution rate and known mean value. Simulations on these dynamical systems are presented to show the effectiveness of the proposed control methods; the former is applied to a wind energy conversion system and the latter is applied to an single machine infinite bus. Both methods are also compared with more traditional methods in their respective applications, those being first order sliding mode controls and the Extended Kalman filter.

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18

Santos, Heron Alves dos. "Design of a controlled single-phase ac-dc converter for interconnection of DC and AC buses of a microgrid". Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12977.

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The recent growth expectation of the participation of solar-photovoltaic energy sources in the power generation matrix has significantly increased the number of grid-connected systems. For connection to power grid, it is essential to use a dc-ac converter, which is able to suit the characteristics of the power provided by the photovoltaic modules to grid parameters. This dissertation presents a project proposal of a 2 kW single phase dc-ac converter for connecting a 311 V dc bus to a 220 Vrms ac bus of a microgrid. The proposed converter is bidirectional and allows, when necessary, the power flow from ac to dc bus. The study shows, through simulation and prototype implementation in the laboratory, that with the application of an appropriate control strategy it is possible to control the direction of power flow, as well as properly modulating the current flowing between two buses, dc, powered by photovoltaic panels and the battery bank, and the ac, at grid side. The prototype had a yield of about 91% and has injected electric current with low harmonic content (THDi less than 5%).
A recente expectativa de crescimento da participaÃÃo da energia solar-fotovoltaica na matriz de geraÃÃo de energia elÃtrica aumentou significativamente o nÃmero de conexÃes desses sistemas Ã rede elÃtrica. Para que a interligaÃÃo com a rede elÃtrica convencional seja possÃvel, Ã indispensÃvel a utilizaÃÃo de conversores CC/CA, capazes de adequar as caracterÃsticas da energia disponibilizada pelos mÃdulos fotovoltaicos aos padrÃes da rede. Esta dissertaÃÃo apresenta uma proposta de projeto de conversor CC/CA de 2 kW para conexÃo de dois barramentos de uma microrrede, um CC em 311 V e outro CA em 220 Vrms. O conversor proposto Ã bidirecional e permite, quando necessÃrio, o fluxo de energia elÃtrica do barramento CA para o CC. O estudo realizado mostra, atravÃs de simulaÃÃes e de implementaÃÃo de protÃtipo em laboratÃrio, que com a aplicaÃÃo de uma estratÃgia de controle adequada Ã possÃvel controlar o sentido do fluxo de potÃncia do conversor, assim como modular apropriadamente a corrente que flui entre dois barramentos, o CC, alimentado por painÃis fotovoltaicos e por banco de baterias, e o barramento CA, do lado da rede elÃtrica. O protÃtipo desenvolvido apresentou rendimento de cerca de 91% e forneceu corrente elÃtrica de baixo conteÃdo harmÃnico (THDi menor que 5%).

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19

Tiwari, Raghbendra. "Application of AC Superconducting Windings in Large PM Synchronous Generators for Wind Power". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18308.

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Superconductors are known for carrying very high current density without any loss of energy. This characteristic helps to achieve very high power capacity with compact size of machine. In application of superconductors, the main obstacle has been the cooling of the conductors since it operates at very low temperatures below ambient. After the discovery of high temperature superconductor (HTS) in 1986, several prototype machines have been built using in DC field winding. The application of superconductor in AC armature winding has not been feasible due to excessive AC losses. These losses are caused due to penetration of time varying magnetic field. This thesis concerns the possibility of the application of superconductor in armature windings of permanent magnet synchronous generator. A 10 MW wind power generator with copper winding has been taken as reference machine and the machine has been redesigned with several pole-slot combinations using superconductor. Permanent magnet has been used as the source of field. Three alternatives have been designed with superconductor in armature winding and the machine with 176 poles, 192 slots has been selected as the best among them based upon the active weight of the generator, outer volume, utilization factor, power factor, full load losses, and total harmonic distortion and cogging torque. The selected machine has been found to be 62 ton in weight where as that of reference machine is 90 ton. Moreover, the outer volume of the superconducting machine is about 2.5 times lesser than that of the copper winding reference machine. The reduction in volume of generator will consequently reduce the volume of nacelle and the reduction in weight will reduce the transportation cost. The major reference of comparison has been the utilization factor of the machines which is 110 kN•m/m3 for the proposed superconducting machine whereas that for reference machine has been 44.6 kN•m/m3. The total loss in superconducting machine has not been calculated due to unavailability of actual AC losses in superconductors. Therefore, a tolerable limit of AC losses has been calculated using the losses incurred by the reference machine which is 0.82 mW/A•m at 20 K when a perpendicular AC field of 0.39 T is applied. Normalized AC losses lower than this value will make the superconducting machine to possess lower loss in comparison to reference machine. Some measures to improve the power factor of superconducting machine by increasing the thickness of magnet have also been studied. It has been found that an increase by 20 mm of additional layer of magnet makes the proposed superconducting machine to have better power factor than the reference machine. Hence, the SC machine consumes less reactive power from the grid and needs a smaller power electronic converter in the system. In this work, it has been put forth that permanent magnet synchronous generators with AC superconductors will make a system compact in size and weight provided AC superconductors with lower losses than aforementioned value are manufactured.

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20

Diver, Carl. "An investigation into novel micro-hole machining techniques for next generation fuel injection nozzle manufacture". Thesis, University of Manchester, 2006. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:207667.

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21

Chen, Yiran. "AC loss analysis and measurement of second generation high temperature superconductor racetrack coils". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648818.

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22

Shen, Boyang. "Study of second generation high temperature superconductors : electromagnetic characteristics and AC loss analysis". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/276688.

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This thesis presents a novel study on Second Generation High Temperature Superconductors, which covers their electromagnetic characteristics and AC loss analysis. Lorentz Force Electrical Impedance Tomography (LFEIT) is one of the most promising hybrid diagnostic scanners with burgeoning potential for biological imaging, particularly in the detection of cancer and internal haemorrhages. The author tried a novel combination of superconducting magnets together with the LFEIT system. The reason is that superconducting magnets can generate a magnetic field with high intensity and homogeneity, which could significantly enhance the electrical signal induced from a sample, thus improving the Signal-to-Noise Ratio (SNR). The author developed four magnet designs for the LEFIT system using the Finite Element Method (FEM) package, COMSOL Multiphysics, and found that a Superconducting Halbach Array magnet can achieve all the requirements (magnetic field properties, geometry, portability, etc.) for the LFEIT system. The optimization study of the superconducting Halbach Array magnet has been carried out on the FEM platform of COMSOL Multiphysics, with 2D models using H-formulation based on B-dependent critical current density and bulk approximation. Optimization focused on the location of the coils, as well as the geometry and number of coils on the premise of maintaining the total amount of superconducting material used in the design. The optimization results showed that the Halbach Array configuration based superconducting magnet is able to generate a magnetic field with an intensity of over 1 Tesla and improved homogeneity. In order to efficiently predict the optimization performance, mathematical formulas were developed for these optimization parameters to determine the intensity and homogeneity of the magnetic field. The mathematical model for the LFEIT system was built based on the theory of the magneto-acousto-electric effect. Then the basic imaging of the electrical signal was developed using Matlab. The magnetic field properties of the magnet design were imported into the LFEIT model. The LFEIT model simulated two samples located in three different magnetic fields with varying magnetic strength and homogeneity. Even if there are no actual alternating currents involved in the DC superconducting magnets mentioned above, they have power dissipation during normal operation (e.g. magnet ramping) and under different background fields. This problem generally goes under the category of “AC loss”. Therefore, the AC loss characteristics of HTS tapes and coils are still fundamentally important for HTS magnet designs, even if they are normally operating in DC conditions. This thesis starts with the AC loss study of HTS tapes. The investigation and comparison of AC losses on Surround Copper Stabilizer (SCS) Tape and Stabilizer-free (SF) Tape have been carried out, which includes AC loss measurement using the electrical method, as well as the real geometry and multi-layer HTS tape simulation using the 2D H formulation by COMSOL Multiphysics. Hysteresis AC losses in the superconducting layer, and eddy current AC losses in the copper stabilizer, silver overlayer and substrate were concerned in this investigation. The measured AC losses were compared to the AC losses from the simulation, using 3 cases of different AC frequency: 10 Hz, 100 Hz, and 1000 Hz. The frequency dependence of AC losses from Stabilizer free Tape and Copper Stabilizer Tape were compared and analysed. A comprehensive AC loss study of a circular HTS coil has been fulfilled. The AC losses from a circular double pancake coil were measured using the electrical method. A 2D axisymmetric H-formulation model using FEM package COMSOL has been established, which was able to make consistency with the real circular coil used in the experiment. To model a circular HTS coil, a 2D axisymmetric model provided better accuracy than a general 2D model, and was also more efficient than a 3D model. Three scenarios were analysed: (1) AC transport current and DC magnetic field, (2) DC transport current and AC magnetic field, (3) AC transport current and AC magnetic field. The angular dependence analysis on the coil under the magnetic field with the different orientation angle  was carried out for all three scenarios. For scenario (3), the effect of the relative phase difference ∆ between the AC current and the AC field on the total AC loss of the coil was investigated. To summarise, a current/field/angle/phase dependent AC loss (I, B, , ∆) study of circular HTS coil has been carried out, which could potentially benefit the future design and research of HTS AC systems. The AC losses of horizontally parallel HTS tapes have been investigated. The AC losses of the middle and end tape of three parallel tapes have been measured using the electrical method, and compared to those of an individual isolated tape. The effect of the interaction between tapes on AC losses has been analysed, and compared with finite element method (FEM) simulations using the 2D H formulation implemented in COMSOL Multiphysics. The electromagnetic induction around the three parallel tapes was monitored using COMSOL simulation. The electromagnetic induction and AC losses generated by a conventional three turn coil were simulated as well, and then compared to the case of three parallel tapes with the same AC transport current. The analysis demonstrated that HTS parallel tapes could be potentially used in wireless power transfer systems, which could have lower total AC losses than conventional HTS coils. By using FEM simulations, cases of increasing number of parallel tapes was considered, and the normalised ratio between the total average AC losses per tape and the AC losses of an individual single tape have been calculated for different gap distances. A new parameter is proposed, Ns, a turning point the for number of tapes, to divide Stage 1 and Stage 2 for the AC loss study of horizontally parallel tapes. For Stage 1, N < Ns, the total average losses per tape increased with the increasing number of tapes. For Stage 2, N > Ns, the total average losses per tape started to decrease with the increasing number of tapes. The analysis demonstrates that horizontally parallel HTS tapes could be potentially used in superconducting devices like HTS transformers, which could retain or even reduce the total average AC losses per tape with large numbers of parallel tapes.

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23

Dalvi, Mahesh. "Computer controlled generation of PWM waveform using harmonic distortion minimization scheme". Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177442328.

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24

Vezenkov, Stoyan Raykov. "Pharmacological studies on the contribution of the neuropeptide proctolin to the cephalic control of singing behavior in grasshopper Chorthippus biguttulus (L. 1758)". Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=974032557.

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25

Shigematsu, Ei. "Study on transport and conversion of ac and dc spin current generated by magnetization dynamics". Doctoral thesis, Kyoto University, 2020. http://hdl.handle.net/2433/245846.

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京都大学
0048
新制・課程博士
博士(工学)
甲第22161号
工博第4665号
新制||工||1728(附属図書館)
京都大学大学院工学研究科電子工学専攻
(主査)教授白石誠司, 教授藤田静雄, 准教授掛谷一弘
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DGAM

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26

Pouresmaeil, Edris. "Advance control of multilevel converters for integration of distributed generation resources into ac grid". Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/83364.

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Distributed generation (DG) with a converter interface to the power grid is found in many of the green power resources applications. This dissertation describes a multi-objective control technique of voltage source converter (VSC) based on multilevel converter topologies, for integration of DG resources based on renewable energy (and non-renewable energy)to the power grid. The aims have been set to maintain a stable operation of the power grid, in case of di erent types of grid-connected loads. The proposed method provides compensation for active, reactive, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently non-linear DG system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the DG output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that signi cantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the DG reference currents, is proposed. The rst step is to extract the DG reference currents from the sensed load currents by applying the stationary reference frame and then transferred into synchronous reference frame method, and then, the reference currents are modi ed, so that the delay will be compensated. The transformed variables are used in control of the multilevel voltage source converter as the heart of the interfacing system between DG resources and power grid. By setting appropriate compensation current references from the sensed load currents in control circuit loop of DG link, the active, reactive, and harmonic load current components will be compensated with fast dynamic response, thereby achieving sinusoidal grid currents in phase with load voltages while required power of loads is more than the maximum injected power of the DG resources. The converter, which is controlled by the described control strategy, guarantees maximum injection of active power to the grid continuously, unity displacement power factor of power grid, and reduced harmonic load currents in the common coupling point. In addition, high current overshoot does not exist during connection of DG link to the power grid, and the proposed integration strategy is insensitive to grid overload.
La Generació Distribuïda (DG) injectada a la xarxa amb un convertidor estàtic és una solució molt freqüent en l'ús de molts dels recursos renovables. Aquesta tesis descriu una técnica de control multi-objectiu del convertidor en font de tensió (VSC), basat en les topologies de convertidor multinivell, per a la integració de les fonts distribuïdes basades en energies renovables i també de no renovables.Els objectius fixats van encaminats a mantenir un funcionament estable de la xarxa elèctrica en el cas de la connexió de diferents tipus de càrregues. El mètode de control proposat ofereix la possibilitat de compensació de les components actives i reactives de la potencia, i les components harmòniques del corrent consumit per les càrregues.La llei de control proporcional-Integral (PI) s’obté de la linearització del model inherentment no lineal del sistema, de forma que el problema de control del corrent injectat i de la tensió d’entrada del convertidor queden desacoblats. Aquest desacoblament permet el control dels corrents de sortida i la tensió del bus de forma independent, però amb un d’ells amb una dinàmica inferior.Per superar els inconvenients del mètode convencional, s’usa un retard computacional, que genera les senyals de referència de forma acurada i sense retard. El primer pas es calcular els corrents de referència a partir de les mesures de corrent. Aquest càlcul es fa primer transformant les mesures a la referència estacionaria per després transformar aquests valors a la referència síncrona. En aquest punt es on es poden compensar els retards.Les variables transformades son usades en els llaços de control del convertidor multinivell. Mitjançant aquests llaços de control i les referències adequades, el convertidor és capaç de compensar la potencia activa, reactiva i els corrents harmònics de la càrrega amb una elevada resposta dinàmica, obtenint uns corrents de la xarxa de forma completament sinusoïdal, i en fase amb les tensions.El convertidor, controlat amb el mètode descrit, garanteix la màxima injecció de la potencia activa, la injecció de la potencia reactiva per compensar el factor de potencia de la càrrega, i la reducció de les components harmòniques dels corrents consumits per la càrrega. A més, garanteix una connexió suau entre la font d’energia i la xarxa. El sistema proposat es insensible en front de la sobrecarrega de la xarxa

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27

Van, Wiltenburg Philip E. "Mitigation of EMI generated by a variable frequency drive controller for an AC induction motor". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA286045.

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28

Siles, Blacutt Carlos. "Direct generation of low frequency single phase AC for the Railway in Norway and Sweden". Thesis, KTH, Elektriska energisystem, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-120116.

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This thesis deals with direct generated electricity for the Swedish and Norwegian railway systems. The form of renewable energy sources that are presented in this thesis is hydropower and a small part is about wind power. Älvkarleby hydropower plant could give redundancy to the Swedish railway system and at the same time solve that problem of locations for static converters close to Stockholm since the land areas close to Stockholm are expensive [14]. A conversion of 50 Hz generators into 16.66 Hz generators in Älvkarleby hydropower plant could lower the pressure on the nearby converter stations which this thesis shows, see Table 6.6. The conversion of a part in Älvkarleby hydropower plant would also strengthen the Swedish railway grid as can be seen in Figure 6.11 and Figure 6.12. If a malfunction would happen in Häggvik converter station as the case was in the fall 2008 [35] and Älvkarleby is functioning it would be possible to have train traffic running. The simulation preformed in this thesis shows that it is possible to have reduced traffic and still have the voltage levels in an acceptable range, see Figure A 4.3 and Figure A 4.4. In 2009 the "132 kV power flow control system" will be introduced for the Swedish railway system. This control system together with direct generation by hydropower could make the idea of hydropower generation attractive as one alternative renewable energy source. Both Norway and Sweden have similar railway systems. The 16.66 Hz electricity price is increasing in Norway and that is one reason why JBV (Jernbaneverket, a company that owns the Norwegian railway grid) chose to renovate one of their two hydropower plants that generates low frequency electricity for the railway. The renovation plans show that JBV sees a profit in renovating their existing low frequency hydropower plants. These aspects are strong arguments to why a reintroduction of hydropower in Sweden could be one alternative solution to more static converters, when dealing with the problem of increasing power consumption.

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29

Zhao, Huiying. "Regulation and Control of AC Microgrid Systems with Renewable Generation and Battery Energy Storage System". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1536342769000338.

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30

Berardi, Alberto. "Studio nel dominio tempo-frequenza di emissioni condotte generate da convertitori elettronici di potenza". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amslaurea.unibo.it/2228/.

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La presente Tesi di Laurea si colloca nell’ambito di un progetto strategico di ateneo chiamato OpIMA. Tale progetto mira a sviluppare codificatori innovativi per segnali di tipo impulsivo, discreti nei livelli, con riferimento soprattutto all’attuazione, alla sintesi di forme d’onda e all’amplificazione audio. L’obiettivo del progetto è di sviluppare nuove generazioni di codificatori, simili nell’uso a quelli tradizionali ed in qualche modo compatibili con essi e pure basati su principi operativi radicalmente diversi. La Tesi di Laurea è stata svolta presso il Dipartimento di Ingegneria Elettrica (DIE) nel laboratorio di Compatibilità Elettromagnetica (LACEM). Il lavoro tratta di uno studio nel dominio tempo-frequenza sulle emissioni condotte prodotte da un convertitore statico DC/AC progettato presso il DIE. Tale studio risulta utile per capire come e quando vengono generati questi disturbi e per migliorare la compatibilità elettromagnetica del convertitore. La Tesi inizialmente richiama con il Capitolo 1 i concetti che stanno alla base della compatibilità elettromagnetica, soprattutto per quanto riguarda le emissioni condotte. Con il Capitolo 2 si descrive in dettaglio il banco prova in ogni sua parte; nel Capitolo 3 vengono riportati i dati teorici di carica e scarica del BUS DC del convertitore. Nel Capitolo 4, 5, 6 vengono riportati i risultati delle prove effettuate sul convertitore per quanto riguarda le emissioni condotte; in particolare nel Capitolo 4 le prove sono state eseguite sul convertitore originale, nel Capitolo 5 si sono ripetute le prove separando elettricamente il circuito di potenza del convertitore da quello di controllo (ovviamente in questa fase abbiamo utilizzato due fonti di alimentazione separate) e nel Capitolo 6 si è voluto eliminare il rumore generato dall’alimentatore presente all’interno del circuito di controllo e per far ciò sono stati costruiti cinque alimentatori lineari esterni con determinate caratteristiche. Infine nell’ultimo Capitolo si sono tratte le conclusioni sui risultati delle misure effettuate.

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Un, Emre. "Common Mode Voltage And Current Reduction In Voltage Source Inverter Driven Three Phase Ac Motors". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609062/index.pdf.

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In this thesis various reduced common mode voltage (RCMV) pulse width modulation (PWM) techniques and active/passive common mode voltage (CMV) reduction methods for voltage source inverter driven three-phase AC motors are theoretically and practically investigated. A novel RCMV-PWM method, the near state PWM (NSPWM) method is proposed for operation at high modulation index. At low modulation index, a modified version of an existing RCMV-PWM method, AZSPWM1, termed as MAZSPWM, is proposed to mitigate the voltage reflection problem of the method. An optimum modulation algorithm combining NSPWM and MAZSPWM with seamless transition is proposed. The proposed RCMV-PWM methods significantly reduce CMV but they suppress common mode current (CMC) partially. Utilization of a common mode inductor together with RCMV-PWM methods is effective in suppressing the CMC. In the study, in addition to the CMV characteristics, various practical performance characteristics such as voltage linearity, inverter output current ripple, inverter DC-link current ripple, and output line-to-line voltage pulse pattern are also analyzed. The study involves analysis, computer simulations, and detailed laboratory experiments.

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32

LaBella, Thomas Matthew. "A High-Efficiency Hybrid Resonant Microconverter for Photovoltaic Generation Systems". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/50526.

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The demand for increased renewable energy production has led to increased photovoltaic (PV) installations worldwide. As this demand continues to grow, it is important that the costs of PV installations decrease while the power output capability increases. One of the components in PV installations that has lots of room for improvement is the power conditioning system. The power conditioning system is responsible for converting the power output of PV modules into power useable by the utility grid while insuring the PV array is outputting the maximum available power. Modular power conditioning systems, where each PV module has its own power converter, have been proven to yield higher output power due to their superior maximum power point tracking capabilities. However, this comes with the disadvantages of higher costs and lower power conversion efficiencies due to the increased number of power electronics converters. The primary objective of this dissertation is to develop a high-efficiency, low cost microconverter in an effort to increase the output power capability and decrease the cost of modular power conditioning systems. First, existing isolated dc-dc converter topologies are explored and a new topology is proposed based on the highly-efficient series resonant converter operating near the series resonant frequency. Two different hybrid modes of operation are introduced in order to add wide input-voltage regulation capability to the series resonant converter while achieving high efficiency through low circulating currents, zero-current switching (ZCS) of the output diodes, zero-voltage switching (ZVS) and/or ZCS of the primary side active switches, and direct power transfer from the source to the load for the majority of the switching cycle. Each operating mode is analyzed in detail using state-plane trajectory plots. A systematic design approach that is unique to the newly proposed converter is presented along with a detailed loss analysis and loss model. A 300-W microconverter prototype is designed to experimentally validate the analysis and loss model. The converter featured a 97.7% weighted California Energy Commission (CEC) efficiency with a nominal input voltage of 30 V. This is higher than any other reported CEC efficiency for PV microconverters in literature to date. Each operating mode of the proposed converter can be controlled using simple fixed-frequency pulse-width modulation (PWM) based techniques, which makes implementation of control straightforward. Simplified models of each operating mode are derived as well as control-to-input voltage transfer functions. A smooth transition method is then introduced using a two-carrier PWM modulator, which allows the converter to transition between operating modes quickly and smoothly. The performance of the voltage controllers and transition method were verified experimentally. To ensure the proposed converter is compatible with different types of modular power conditioning system architectures, system-level interaction issues associated with different modular applications are explored. The first issue is soft start, which is necessary when the converter is beginning operation with a large capacitive load. A novel soft start method is introduced that allows the converter to start up safely and quickly, even with a short-circuited output. Maximum power point tracking and double line frequency ripple rejection are also explored, both of which are very important to ensuring the PV module is outputting the maximum amount of available power. Lastly, this work deals with efficiency optimization of the proposed converter. It is possible to use magnetic integration so that the resonant inductor can be incorporated into the isolation transformer by way of the transformer leakage inductance in order to reduce parts count and associated costs. This chapter, however, analyzes the disadvantages to this technique, which are increased proximity effect losses resulting in higher conduction losses. A new prototype is designed and tested that utilizes an external resonant inductor and the CEC efficiency was increased from 97.7% to 98.0% with a marginal 1.8% total cost increase. Additionally, a variable frequency efficiency optimization algorithm is proposed which increases the system efficiency under the high-line and low-line input voltage conditions. This algorithm is used for efficiency optimization only and not control, so the previously presented simple fixed-frequency modeling and control techniques can still be utilized.
Ph. D.

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33

BAIG, CLEMENT RANJITH ANTHIKKAD &amp IRFAN AHMED. "PERFORMANCE ENHANCEMENT OF OFDM IN PAPR REDUCTION USING NEW COMPANDING TRANSFORM AND ADAPTIVE AC EXTENSION ALGORITHM FOR NEXT GENERATION NETWORKSPERFORMANCE ENHANCEMENT OF OFDM IN PAPR REDUCTION USING NEW COMPANDING TRANSFORM AND ADAPTIVE AC EXTENSION ALGORITHM FOR NEXT GENERATION NETWORKS". Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-6011.

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This paper presents a new hybrid PAPR reduction technique for the OFDM signal, which combines a multiple symbol representations method with a signal clipping method. The clipping method is a nonlinear PAPR reduction scheme, where the amplitude of the signal is limited to a given threshold. Considering the fact that the signal must be interpolated before A/D conversion, a variety of clipping methods has been proposed. Some methods suggest the clipping before interpolation, having the disadvantage of the peaks re-growth. Other methods contributed that the clipping after interpolation, having the disadvantage of out-of-band power production. In order to overcome this problem different filtering techniques have been proposed. Filtering can also cause peak re-growth, but less than the clipping before interpolation. Another clipping technique supposes that only subcarriers having the highest phase difference between the original signal and its clipped variant will be changed. This is the case of the partial clipping method. To further reduce the PAPR, the dynamic of the clipped signal can be compressed. Linear methods like partial transmit sequence or selective mapping has been proposed for the reduction of PAPR as well. Another PAPR reduction method is the tone reservation. It uses tones on which no data is sent to reduce the transmitted signal peaks. Derivatives of this method with lower computation complexity and improved performance have been proposed: One-Tone One-Peak and one by-one iteration. A similar PAPR reduction method is the multiple symbol representations, where alternative signalling points are used to represent one symbol. The simulation results highlight the advantages of the proposed PAPR reduction method.
The proposed technique namely Adaptive Active Constellation Extension (Adaptive ACE) Algorithm reduced the high Peak-to-Average Power Ratio (PAPR) of the Orthogonal Frequency Division Multiplexing (OFDM) systems. The Peak-to-Average Power Ratio (PAPR) is equal to 6.8 dB for the target clipping ratios of 4 dB, 2 dB and 0 dB by using Adaptive Active Constellation Extension (Adaptive ACE) Algorithm. Thus, the minimum PAPR can be achieved for low target clipping ratios. The Signal-to-Noise Ratio (SNR) of the Orthogonal Frequency Division Multiplexing (OFDM) signal obtained by the Adaptive Active Constellation Extension (Adaptive ACE) algorithm is equal to 1.2 dB at a Bit Error Rate (BER) of 10-0..4 for different constellation orders like 4-Quadrature Amplitude Modulation (4-QAM), 16-Quadrature Amplitude Modulation (16-QAM) and 64-Quadrature Amplitude Modulation (16-QAM). Here, the Bit Error Rate of 10-0.4 or 0.398, that means a total of 398-bits are in error when 1000-bits are transmitted via a communication channel or approximately 4-bits are in error when 10-bits are transmitted via a communication channel, which is high when compared to that of the original Orthogonal Frequency Division Multiplexing (OFDM) signal. The other problems faced by the Adaptive Active Constellation Extension (Adaptive ACE) algorithm are Out-of-Band Interference (OBI) and peak regrowth. Here, the Out-of-Band Interference (OBI) is a form of noise or an unwanted signal, which is caused when the original Orthogonal Frequency Division Multiplexing (OFDM) signal is clipped for reducing the peak signals which are outside of the predetermined area and the peak regrowth is obtained after filtering the clipped signal. The peak regrowth results to, increase in the computational time and computational complexity. In this paper, we have proposed a PAPR reduction scheme to improve the bit error rate performance by applying companding transform technique. Hence, 1-1.5 dB reduction in PAPR with this Non-companding technique is achieved. In Future, We can accept to implement the same on Rician and Rayleigh channels.
Clement Ranjith Anthikkad (E-mail: clement.ranjith@gmail.com / clan11@bth.se) & Irfan Ahmed Baig (E-mail: baig.irfanahmed@gmail.com / ir-a11@bth.se )

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Zhang, YuQi. "ADVANCED SYNCHRONOUS MACHINE MODELING". UKnowledge, 2018. https://uknowledge.uky.edu/ece_etds/118.

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The synchronous machine is one of the critical components of electric power systems. Modeling of synchronous machines is essential for power systems analyses. Electric machines are often interfaced with power electronic components. This work presents an advanced synchronous machine modeling, which emphasis on the modeling and simulation of systems that contain a mixture of synchronous machines and power electronic components. Such systems can be found in electric drive systems, dc power systems, renewable energy, and conventional synchronous machine excitation. Numerous models and formulations have been used to study synchronous machines in different applications. Herein, a unified derivation of the various model formulations, which support direct interface to external circuitry in a variety of scenarios, is presented. Selection of the formulation with the most suitable interface for the simulation scenario has better accuracy, fewer time steps, and less run time. Brushless excitation systems are widely used for synchronous machines. As a critical part of the system, rotating rectifiers have a significant impact on the system behavior. This work presents a numerical average-value model (AVM) for rotating rectifiers in brushless excitation systems, where the essential numerical functions are extracted from the detailed simulations and vary depending on the loading conditions. The proposed AVM can provide accurate simulations in both transient and steady states with fewer time steps and less run time compared with detailed models of such systems and that the proposed AVM can be combined with AVM models of other rectifiers in the system to reduce the overall computational cost. Furthermore, this work proposes an alternative formulation of numerical AVMs of machine-rectifier systems, which makes direct use of the natural dynamic impedance of the rectifier without introducing low-frequency approximations or algebraic loops. By using this formulation, a direct interface of the AVM is achieved with inductive circuitry on both the ac and dc sides allowing traditional voltage-in, current-out formulations of the circuitry on these sides to be used with the proposed formulation directly. This numerical AVM formulation is validated against an experimentally validated detailed model and compared with previous AVM formulations. It is demonstrated that the proposed AVM formulation accurately predicts the system's low-frequency behavior during both steady and transient states, including in cases where previous AVM formulations cannot predict accurate results. Both run times and numbers of time steps needed by the proposed AVM formulation are comparable to those of existing AVM formulations and significantly decreased compared with the detailed model.

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35

You, Keping Electrical Engineering &amp Telecommunications Faculty of Engineering UNSW. "A new bidirectional AC-DC converter using matrix converter and Z-source converter topologies". Awarded by:University of New South Wales, 2007. http://handle.unsw.edu.au/1959.4/37450.

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This thesis proposes a new bidirectional three-phase AC-DC power converter using matrix converter and Z-source inverter topologies. Advantages of the AC-DC matrix converter are the inherently controllable power factor, the tight DC voltage regulation, the wide bandwidth with quick response to load variation, the single-stage buck-voltage AC-to-DC power conversion; advantages of the z-source inverter are the increased reliability by allowing the shoot-through between upper and lower power switches of one inverter leg, insensitivity to DC bus voltage due to the extra freedom of controlling DC-link voltage. The proposed Matrix-Z-source converter (MZC) marries up both advantages of AC-DC matrix converter and Z-source inverter. It can achieve voltage-boost DC-AC inversion capable of variable voltage variable frequency (VVVF) AC output; it can achieve voltage-buck AC-DC rectification capable of inherent control over AC current phase angle and DC output regulation with a (VVVF) AC source supply. Both foresaid performance in DC-AC inversion and AC-DC rectification can be implemented in a simple open-loop control manner. Three constraints of VSI, in the bidirectional AC-DC power conversion, are the peak AC voltages are always less than DC-link voltage, closed-loop control has to be employed when DC regulation and/or AC current phase angle control are required, and AC voltage is sensitive to the variation of the DC-link voltage in DC-AC inversion. The voltage-boost inversion and/or voltage-buck rectification of MZC overcomes the first constraint; thus MZC enables the AC machine voltage increased higher than DC-link voltage hence advantages of running AC machine at relatively high voltages are enabled. The direct DC voltage regulation and inherent AC-current-phase-angle control of MZC overcomes the second constraint in an open-loop manner; hence a simplified system design is obtained with sufficient room for the further improvement by closed-loop control schemes. The extra freedom in controlling DC-link voltage of MZC overcomes the third constraint hence a DC source voltage adaptable inverter is obtained. This thesis focuses on the study of the feasibility of the proposed MZC through theoretical analysis and experimental verification. At first, the proposed MZC is conceptually constructed by examining the quadrant operation of AC-DC matrix converter and Z-source inverter. After the examination of the operating principles of both AC-DC matrix converter and Z-source inverter, the configuration of MZC is then proposed. The MZC has two operating modes: DC-AC inversion and AC-DC rectification. Circuit analysis for both operating modes shows that the new topology does not impose critical conflict in circuit design or extra restriction in parameterization. On the contrary, one version of the proposed MZC can make full advantage of Z-source network components in both operating modes, i.e. a pair of Z-source inductor and capacitor can be used as low-pass filter in AC-DC rectification. The modulation strategy, average modeling of system, and features of critical variables for circuit design of the proposed MZC were examined for each operating mode. Simulations of the proposed MZC and its experimental verification have been presented. Analytical models of conduction and switching losses of the power-switch network in different operating mode have shown that the losses in the MZC compare favorably with conventional VSI for a range of power factor and modulation indices.

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36

Yuan, Weijia. "Second-generation high-temperature superconducting coils and their applications for energy storage". Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/229754.

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Since a superconductor has no resistance below a certain temperature and can therefore save a large amount of energy dissipated, it is a 'green' material by saving energy loss and hence reducing carbon emissions. Recently the massive manufacture of high-temperature superconducting (HTS) materials has enabled superconductivity to become a preferred candidate to help generation and transportation of cleaner energy. One of the most promising applications of superconductors is Superconducting Magnetic Energy Storage (SMES) systems, which are becoming the enabling engine for improving the capacity, efficiency, and reliability of the electric system. SMES systems store energy in the magnetic field created by the flow of direct current in a superconducting coil. SMES systems have many advantages compared to other energy storage systems: high cyclic efficiency, fast response time, deep discharge and recharge ability, and a good balance between power density and energy density. Based on these advantages, SMES systems will play an indispensable role in improving power qualities, integrating renewable energy sources and energizing transportation systems. This thesis describes an intensive study of superconducting pancake coils wound using second-generation(2G) HTS materials and their application in SMES systems. The specific contribution of this thesis includes an innovative design of the SMES system, an easily calculated, but theoretically advanced numerical model to analyse the system, extensive experiments to validate the design and model, and a complete demonstration experiment of the prototype SMES system. This thesis begins with literature review which includes the introduction of the background theory of superconductivity and development of SMES systems. Following the literature review is the theoretical work. A prototype SMES system design, which provides the maximum stored energy for a particular length of conductors, has been investigated. Furthermore, a new numerical model, which can predict all necessary operation parameters, including the critical current and AC losses of the system, is presented. This model has been extended to analyse superconducting coils in different situations as well. To validate the theoretical design and model, several superconducting coils, which are essential parts of the prototype SMES system, together with an experimental measurement set-up have been built. The coils have been energized to test their energy storage capability. The operation parameters including the critical current and AC losses have been measured. The results are consistent with the theoretical predictions. Finally the control system is developed and studied. A power electronics control circuit of the prototype SMES system has been designed and simulated. This control circuit can energize or discharge the SMES system dynamically and robustly. During a voltage sag compensation experiment, this SMES prototype monitored the power system and successfully compensated the voltage sag when required. By investigating the process of building a complete system from the initial design to the final experiment, the concept of a prototype SMES system using newly available 2G HTS tapes was validated. This prototype SMES system is the first step towards the implementation of future indsutrial SMES systems with bigger capacities, and the knowledge obtained through this research provides a comprehensive overview of the design of complete SMES systems.

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37

Gonçalves, Amilcar Flamarion Querubini. "Sistema de geração distribuída controlado em tensão e potência e utilizado de forma isolada ou conectada à rede de distribuição". Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-28012016-080537/.

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Esta tese apresenta uma estratégia de controle para gerenciar a potência entregue ou absorvida da rede, independente de características das cargas locais. Para atingir este objetivo é utilizado um inversor fonte de tensão (VSI) que funcionará semelhante a um sistema de geração distribuída (GD) ou como um filtro ativo. O VSI é controlado por meio de controladores clássicos em cascata, nos quais a malha interna é utilizado para estabilizar a corrente e a malha externa controla a tensão nos terminais de saída da GD. Para melhorar a resposta do VSI são colocados filtros ressonantes em paralelo ao controlador de tensão (P+RES). Além disso, as respostas dos filtros ressonantes são melhoradas através da utilização de um método adequado de discretização, no qual os coeficientes são alterados dinamicamente mediante a frequência de sincronismo produzido pelo algoritmo de sincronismo (PLL). O controle de potência apresenta duas estruturas de controle em malha fechada: uma para controlar a potência reativa através da rede pelo ajuste da amplitude da tensão da GD, e o outra para controlar a potência ativa, modificando o ângulo de defasagem entre as tensões da rede e as tensões GD. Por fim, um conjunto de simulações e resultados experimentais é apresentado para validar todas as propostas deste trabalho.
This thesis presents a control strategy to manage the power delivered to or absorbed from the grid, independently of the local load characteristics. To achieve this goal, a voltage source inverter (VSI) will work as a distributed generation system (DG) or according to active filter. The VSI will be controlled by means of a double cascade classical controller, in which the inner loop is used to stabilize the VSI output current and the outer loop controls the DG terminal voltage. To improve the response of the VSI, resonant filters are placed in parallel. Additionally, resonant filter dynamic responses are enhanced through the use of a proper discretization method, in which the coefficients are changed dynamically by means of the synchronism frequency produced by the phase-locked loop (PLL) algorithm. This study also exhibits two closed-loop structures: one to control the reactive power through the grid by adjusting the DG voltage amplitude, and the other to control the active power by modifying the angle of displacement between the grid and the DG voltages. Both power control structures operate adequately in decoupled operation mode, so that one has a faster dynamic response than the other. To verify all statements proposed in this thesis, a set of simulations and experimental results are presented.

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38

Dalík, Vladimír. "Číslicově řízený zdroj střídavého napětí". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218319.

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The thesis deals of microprocesor controlled instrument for measuring. In general it is about of controlling instruments and their usage in standard industry. laboratories and measuring systems. The first part contens theoretical knowledge of controlling instrument, his funtions and describes circuitry of sources of AC voltages. This part describes blocks of instrument and basis connecting in system of instrument. Each block is described with examples in praxis. Examples contents typical connecting and their problems out of view in parameters of instrumenr. In this part is whole theory of analysis and practical using separately parts of instrument. Next part is aimed at searching of interrelationship between the teoretical model of source that described by different circuits and practical connections with electronic parts. These part analyse concrete design with exactly sized parameters and connections. In last part contents describing of measuring at prototype. The appendix contains schematics and boards with electronic parts and test reports of measuring output voltage and frequency with required accuracies.

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39

Sahoo, Smrutirekha. "Impact Study: Photo-voltaic Distributed Generation on Power System". Thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-32369.

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The grid-connected photo-voltaic (PV) system is one of the most promising renewable energy solutions which offers many benefits to both the end user and the utility network and thus it has gained the popularity over the last few decades. However, due to the very nature of its invariability and weather dependencies, the large scale integration of this type of distributed generation has created challenges for the network operator while maintaining the quality of the power supply and also for reliable and safe operations of the grids. In this study, the behavioral impact of large scale PV system integration which are both steady and dynamic in nature was studied. An aggregate PV model suited to study the impacts was built using MATLAB/Simulink. The integration impacts of PV power to existing grids were studied with focus on the low voltage residential distribution grids of Mälarenergi Elnät AB (10/0.4 kV). The steady state impacts were related to voltage profile, network loss. It was found that the PV generation at the load end undisputedly improves the voltage profile of the grid especially for the load buses which are situated at farther end of the grid. Further, with regard to the overvoltage issue, which is generally a concern during the low load demand period it was concluded that, at a 50% PV penetration level, the voltage level for the load buses is within the limit of 103% as prescribed by the regulator excepting for few load buses. The voltage level for load buses which deviate from the regulatory requirement are located at distance of 1200 meter or further away from the substation. The dynamic impact studied were for voltage unbalancing in the grid, which was found to have greater impact at the load buses which is located farther compared to a bus located nearer to the substation. With respect to impact study related to introduction of harmonics to the grid due to PV system integration, it was found that amount of harmonic content which was measured as total harmonic distortion (THD) multiplies with integration of more number of PV system. For a 50 % penetration level of PV, the introduced harmonics into the representative network is very minimal. Also, it was observed from the simulation study that THD content are be less when the grid operates at low load condition with high solar irradiance compared to lower irradiance and high load condition.

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40

Carvalho, Marina Silva Camillo de. "Análise de técnicas de detecção de ilhamento ativas em sistemas de geração distribuída baseados em inversores fonte de tensão". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-02082017-164542/.

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A abordagem principal desse trabalho é o estudo de técnicas anti-ilhamento ativas com realimentação positiva em um sistema de Geração Distribuída (GD) composto por um Inversor Fonte de Tensão (VSI,do inglês Voltage Source Inverter) e com cargas locais conectadas em paralelo. Na literatura são encontrados dois grupos de técnicas empregadas como proteção anti-ilhamento: as ativas e as passivas. Os métodos de detecção de ilhamento ativos são utilizados, pois possuem menores zonas de não detecção em comparação às técnicas passivas, porém injetam distúrbios contínuos no sistema de GD. Esses distúrbios degradam a qualidade de energia elétrica fornecida pelo conversor eletrônico. Nesse contexto, como escopo dessa dissertação, é realizado o estudo da estrutura de controle empregada no sistema de GD conectado com a rede de distribuição, com o intuito de avaliar o funcionamento do gerenciamento de tensão e de potência ativa e reativa. E em seguida, são discutidas técnicas de detecção de ilhamento ativas em frequência e tensão, ambas, com realimentação positiva e ganho fixo com o objetivo de investigar o desempenho das mesmas em relação ao tempo de detecção e a injeção de distúrbios no sistema de controle da GD. A partir dessa análise, são desenvolvidas técnicas anti-ilhamento com intuito de reduzir a injeção de distúrbios em diferentes pontos de operação da GD e garantir uma eficiência semelhante aos métodos tradicionais em casos de difícil detecção. Essas técnicas são baseadas na implementação do cálculo de um ganho com realimentação positiva variável inversamente proporcional a variação de potência ativa ou reativa entregue a rede. Para validação das propostas presentes nesta dissertação, são obtidos resultados em simulações computacionais e, posteriormente são adquiridos resultados práticos através de uma bancada experimental compatível com o sistema de GD simulado.
The main approach of this thesis is the study of active anti-islanding techniques with positive feedback in a Distributed Generation (DG) system composed by a Voltage Source Inverter (VSI) and local loads. In literature two groups of techniques are used as anti-island protection: the active and the passive techniques. The active islanding detection methods are preferably used because of the smaller non-detection zones compared to passive techniques, however they inject continuous disturbances in the DG system, reducing the power quality provided by the VSI. In this context, as the scope of this dissertation, it is firstly carried out the study of control structures employed in grid-tied distribution system, to evaluate the operation of the voltage control loops, and the active-and reactive power managements. Additionally, we discuss active islanding detection techniques in frequency and voltage with positive feedback and constant gain, based on the classical, with the objective of investigating their performance in relation to the detection time and the injection of disturbances in the DG system. From this analysis, antiislanding techniques are developed to guarantee efficiency similar to the traditional methods in cases of small-power flow through the grid and minimize disturbances. These techniques are based on the calculation of the positive feedback variable gain inversely proportional to the deviation of active or reactive power delivered or absorbed from the grid. To validate this proposal, the results are obtained through computational simulations and experimental analysis, as well.

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41

Keeli, Anupama. "Low frequency transmission for remote power generating systems". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41190.

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The goal of this Masters Thesis research is to evaluate alternative transmission systems from remote wind farms to the main grid using low-frequency AC technology. Low frequency means a frequency lower than nominal frequency (60/50Hz). The low-frequency AC network can be connected to the power grid at major substations via cyclo-converters that provide a low-cost interconnection and synchronization with the main grid. Cyclo-converter technology is utilized to minimize costs which result in systems of 20/16.66 Hz (for 60/50Hz systems respectively). Low frequency transmission has the potential to provide an attractive solution in terms of economics and technical merits.

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42

Makhalas, Kharsan Al y Faisal Alsehlli. "Wind Power". Thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-4336.

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This Bachelor thesis has been written at the Blekinge Institute of Technology. This thesis concentrates on the wind power and their components, also the large wind farm is studied. The electrical power is generated by using the power in wind to drive a wind turbine to produce mechanical power. This mechanical power can be converted into electrical power by using electrical induction generators. There are two types of the wind turbines, the horizontal axis and vertical axis wind turbine, where the horizontal axis wind turbine is mostly used and was studied in this thesis. The rotor can be placed in two directions: an upwind rotor where the blade of turbine faces to the wind, so it operates more smoothly and transmit more power. The other type is a downwind rotor which orients itself with respect for the wind direction. Moreover, the tower shadow makes the blade to flex, consequently resulting in fatigue, noise, and reduces output of the power. The modern wind turbine has been built with an odd number of blades which is important for the stability of the turbine. The rotor with an odd number of blades can be considered to be similar to a disc when calculating the dynamic properties of the machine. The main idea of this thesis is to study the wind power in general and large wind parks specifically. The Horns Rev wind park was taken as an example of a wind park in Denmark and the Gotland wind park as an example of a wind park in Sweden too. Into account, the distance between wind turbine in the wind direction cannot be too small. If the wind turbines are located to close to each other, the wind will be more and more turbulent after it passes through each single wind turbine. This would lead to that wind turbines downstream in the wind park, and it might even have to shut down due to that mechanical loading gets to high during strong conditions. This is due to the fact that when wind passes through the rotor of the wind turbine it gets very turbulent and the wind speed is decreased. The minimum length of the rotor should be approximately 5-7 rotor diameters to avoid that issue. Gotland Energy AB (GEAB) considered, that high voltage direct current light would be the only realistic way to solve the technical problems for the high amount of wind power in-feed. One result is that The stability of voltage during transient events, has become much better by using the high voltage direct current light so that the output current stability from the asynchronous generators have been improved, which reduces the stresses on the AC grid and on the mechanical construction of the windmills.
In general the wind turbines with three blades accommodated a thicker root are used. It is obvious that, the less number of blades on the wind turbine, the cost of material and manufacturing will be lower. It is worthy to mentioned that, the modern wind turbine has been built with an odd number of blades. When the length of the blade increases the deflection of blade tip due to axial wind force also increase as well. So without consider the increase in length of blade may lead to dangerous situation of collision of tower and blade. Moreover, by increasing the number of blades cost of the system would increased as well. The limit of transfer for the AC transmission system depends on the distance from shore and is therefore physically limited by this. AC large wind parks that are placed at a long distance from the shore, which means AC long transmission line, and more drop voltage A solution to AC long transmission line, it could be to decrease the offshore frequency and use a low frequency AC networks. There is a suggestion by for instance (Schütte, Gustavsson and Ström 2011). The usages of a low frequency system are in electrified railway systems, where the frequency ranges from 16.67 Hz to 25 Hz. However, the network of a low frequency would allow a simpler design of the offshore WTs and The aerodynamic rotor of a large WT operates at maximum revolutions at 15-20 rpm. The lower frequency would then allow a smaller gear ratio for turbines with a gearbox, or decrease the poles number for WTs with direct driven generators. This would lead to lighter and cheaper turbines. One of the disadvantages by using a low frequency system is the size of transformer would be increased, and hence, the costs of transformer will increased too. The operator of the grid, Gotland Energy AB (GEAB) considered, that HVDC light would be the only realistic way to solve the technical problems for the high amount of wind power in-feed. The experiences have supported expected improvements in the characteristics for example: - Stability in the system arose. - Reactive demands, power flows, as well as voltage level in the harmonic and system were reduced. - Flicker problems were eliminated with the installation of HVDC light and transient phenomena disappeared. Moreover, Overall experiences of Gotland Energy AB (GEAB) are that the control of power flow from the converters makes the AC grid easier to observe than a conventional AC network and the power variations do not stress the AC grid as much as in normal network. Voltage quality has been better with the increased wind power production. A topic to study in the future is the consequences of blackouts in power supply with many wind power farm.
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Aguiar, Cassius Rossi de. "Estudo e análise de algoritmos de detecção de ilhamento em sistemas de geração distribuída conectados à rede de distribuição". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-12112013-152823/.

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Este trabalho aborda a detecção da condição de ilhamento e de seus impactos em redes de distribuição e em gerações distribuídas que empregam conversores CC-CA. Na literatura são encontradas dois grupos de técnicas para este tipo de aplicação. As técnicas passivas, que identificam a condição de ilhamento através do ajuste dos limites de variação dos relés de proteção, e as técnicas ativas, que inserem um sinal de realimentação positiva de forma a tornar o sistema instável no momento da desconexão. As técnicas ativas, por apresentarem um menor tempo de detecção e simples implementação em hardware, são preferencialmente utilizadas, apesar da injeção de distúrbios no sistema de controle da geração distribuída. O estado-da-arte em termos de detecção de ilhamento consiste em desenvolver uma técnica que possua alta capacidade de detecção, porém sem injeção de distúrbios no sistema de geração distribuída quando conectado à rede de distribuição. Neste trabalho, são abordadas duas formas para a redução da injeção de distúrbios e do tempo de detecção. Em uma primeira abordagem é proposto um projeto ótimo para o algoritmo de sincronização PLL (phase-locked loop), o qual permite a redução do ganho de realimentação positiva para técnicas em frequência e, consequentemente, a redução da injeção de distúrbios. Em uma segunda abordagem é utilizada a metodologia fuzzy de forma a garantir a detecção da condição de ilhamento sem nenhuma injeção de distúrbios no sistema de controle. Resultados de simulação e experimentais, obtidos por meio de uma bancada experimental controlada por DSP, são apresentados para validar as propostas presentes nesta dissertação
This thesis deals with the islanding detection and its impact on distribution networks when distributed generation systems are driven by DC-AC converters. Two groups of techniques are found in the literature. The passive techniques in which adjusting the variation limits of protective relays identify the islanding condition, and the active techniques that insert a positive feedback signal in order to make the system unstable when the contingency is on progress. The active techniques present a reduced detection time and simple hardware implementation. They are preferably used in despite of the injection of disturbances in the control system. In this thesis two ways to reduce injection of disturbances and detection time are proposed. In a first approach is shown an optimal design for the synchronization algorithm PLL (Phase-Locked Loop) which allows to reduce the positive feedback gain in frequency techniques in order to decrease the injection of disturbances. In a second approach a fuzzy methodology is used to ensure the islanding detection with the aforementioned requirements. Simulation analysis and experimental results are presented to validate the proposed approach

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Zadeh, Ramin Agha. "Performance control of distributed generation using digital estimation of signal parameters". Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/47011/1/Ramin_Agha_Zadeh_Thesis.pdf.

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The Queensland University of Technology (QUT) allows the presentation of a thesis 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 seven published/submitted papers, of which one has been published, three accepted for publication and the other three are under review. This project is financially supported by an Australian Research Council (ARC) Discovery Grant with the aim of proposing strategies for the performance control of Distributed Generation (DG) system with digital estimation of power system signal parameters. Distributed Generation (DG) has been recently introduced as a new concept for the generation of power and the enhancement of conventionally produced electricity. Global warming issue calls for renewable energy resources in electricity production. Distributed generation based on solar energy (photovoltaic and solar thermal), wind, biomass, mini-hydro along with use of fuel cell and micro turbine will gain substantial momentum in the near future. Technically, DG can be a viable solution for the issue of the integration of renewable or non-conventional energy resources. Basically, DG sources can be connected to local power system through power electronic devices, i.e. inverters or ac-ac converters. The interconnection of DG systems to power system as a compensator or a power source with high quality performance is the main aim of this study. Source and load unbalance, load non-linearity, interharmonic distortion, supply voltage distortion, distortion at the point of common coupling in weak source cases, source current power factor, and synchronism of generated currents or voltages are the issues of concern. The interconnection of DG sources shall be carried out by using power electronics switching devices that inject high frequency components rather than the desired current. Also, noise and harmonic distortions can impact the performance of the control strategies. To be able to mitigate the negative effect of high frequency and harmonic as well as noise distortion to achieve satisfactory performance of DG systems, new methods of signal parameter estimation have been proposed in this thesis. These methods are based on processing the digital samples of power system signals. Thus, proposing advanced techniques for the digital estimation of signal parameters and methods for the generation of DG reference currents using the estimates provided is the targeted scope of this thesis. An introduction to this research – including a description of the research problem, the literature review and an account of the research progress linking the research papers – is presented in Chapter 1. One of the main parameters of a power system signal is its frequency. Phasor Measurement (PM) technique is one of the renowned and advanced techniques used for the estimation of power system frequency. Chapter 2 focuses on an in-depth analysis conducted on the PM technique to reveal its strengths and drawbacks. The analysis will be followed by a new technique proposed to enhance the speed of the PM technique while the input signal is free of even-order harmonics. The other techniques proposed in this thesis as the novel ones will be compared with the PM technique comprehensively studied in Chapter 2. An algorithm based on the concept of Kalman filtering is proposed in Chapter 3. The algorithm is intended to estimate signal parameters like amplitude, frequency and phase angle in the online mode. The Kalman filter is modified to operate on the output signal of a Finite Impulse Response (FIR) filter designed by a plain summation. The frequency estimation unit is independent from the Kalman filter and uses the samples refined by the FIR filter. The frequency estimated is given to the Kalman filter to be used in building the transition matrices. The initial settings for the modified Kalman filter are obtained through a trial and error exercise. Another algorithm again based on the concept of Kalman filtering is proposed in Chapter 4 for the estimation of signal parameters. The Kalman filter is also modified to operate on the output signal of the same FIR filter explained above. Nevertheless, the frequency estimation unit, unlike the one proposed in Chapter 3, is not segregated and it interacts with the Kalman filter. The frequency estimated is given to the Kalman filter and other parameters such as the amplitudes and phase angles estimated by the Kalman filter is taken to the frequency estimation unit. Chapter 5 proposes another algorithm based on the concept of Kalman filtering. This time, the state parameters are obtained through matrix arrangements where the noise level is reduced on the sample vector. The purified state vector is used to obtain a new measurement vector for a basic Kalman filter applied. The Kalman filter used has similar structure to a basic Kalman filter except the initial settings are computed through an extensive math-work with regards to the matrix arrangement utilized. Chapter 6 proposes another algorithm based on the concept of Kalman filtering similar to that of Chapter 3. However, this time the initial settings required for the better performance of the modified Kalman filter are calculated instead of being guessed by trial and error exercises. The simulations results for the parameters of signal estimated are enhanced due to the correct settings applied. Moreover, an enhanced Least Error Square (LES) technique is proposed to take on the estimation when a critical transient is detected in the input signal. In fact, some large, sudden changes in the parameters of the signal at these critical transients are not very well tracked by Kalman filtering. However, the proposed LES technique is found to be much faster in tracking these changes. Therefore, an appropriate combination of the LES and modified Kalman filtering is proposed in Chapter 6. Also, this time the ability of the proposed algorithm is verified on the real data obtained from a prototype test object. Chapter 7 proposes the other algorithm based on the concept of Kalman filtering similar to those of Chapter 3 and 6. However, this time an optimal digital filter is designed instead of the simple summation FIR filter. New initial settings for the modified Kalman filter are calculated based on the coefficients of the digital filter applied. Also, the ability of the proposed algorithm is verified on the real data obtained from a prototype test object. Chapter 8 uses the estimation algorithm proposed in Chapter 7 for the interconnection scheme of a DG to power network. Robust estimates of the signal amplitudes and phase angles obtained by the estimation approach are used in the reference generation of the compensation scheme. Several simulation tests provided in this chapter show that the proposed scheme can very well handle the source and load unbalance, load non-linearity, interharmonic distortion, supply voltage distortion, and synchronism of generated currents or voltages. The purposed compensation scheme also prevents distortion in voltage at the point of common coupling in weak source cases, balances the source currents, and makes the supply side power factor a desired value.

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Rahimi, Arian. "Design And Implementation Of Low Power Interface Electronics For Vibration-based Electromagnetic Energy Harvesters". Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613820/index.pdf.

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For many years batteries have been used as the main power sources for portable electronic devices. However, the rate of scaling in integrated circuits and micro-electro-mechanical systems (MEMS) has been much higher than that of the batteries technology. Therefore, a need to replace these temporary energy reservoirs with small sized continuously charged energy supply units has emerged. These units, named as energy harvesters, use several types of ambient energy sources such as heat, light, and vibration to provide energy to intelligent systems such as sensor nodes. Among the available types, vibration based electromagnetic (EM) energy harvesters are particularly interesting because of their simple structure and suitability for operation at low frequency values (<
10 Hz), where most vibrations exits. However, since the generated EM power and voltage is relatively low at low frequencies, high performance interface electronics is required for efficiently transferring the generated power from the harvester to the load to be supplied. The aim of this study is to design low power and efficient interface electronics to convert the low voltage and low power generated signals of the EM energy harvesters to DC to be usable by a real application. The most critical part of such interface electronics is the AC/DC converter, since all the other blocks such as DC/DC converters, power managements units, etc. rely on the rectified voltage generated by this block. Due to this, several state-of-the-art rectifier structures suitable for energy harvesting applications have been studied. Most of the previously proposed rectifiers have low conversion efficiency due to the high voltage drop across the utilized diodes. In this study, two rectifier structures are proposed: one is a new passive rectifier using the Boot Strapping technique for reducing the diode turn-on voltage values
the other structure is a comparator-based ultra low power active rectifier. The proposed structures and some of the previously reported designs have been implemented in X-FAB 0.35 µ
m standard CMOS process. The autonomous energy harvesting systems are then realized by integrating the developed ASICs and the previously proposed EM energy harvester modules developed in our research group, and these systems have been characterized under different electromechanical excitation conditions. In this thesis, five different systems utilizing different circuits and energy harvesting modules have been presented. Among these, the system utilizing the novel Boot Strap Rectifier is implemented within a volume of 21 cm3, and delivers 1.6 V, 80 µ
A (128 µ
W) DC power to a load at a vibration frequency of only 2 Hz and 72 mg peak acceleration. The maximum overall power density of the system operating at 2 Hz is 6.1 µ
W/cm3, which is the highest reported value in the literature at this operation frequency. Also, the operation of a commercially available temperature sensor using the provided power of the energy harvester has been shown. Another system utilizing the comparator-based active rectifier implemented with a volume of 16 cm3, has a dual rail output and is able to drive a 1.46 V, 37 µ
A load with a maximum power density of 6.03 µ
W/cm3, operating at 8 Hz. Furthermore, a signal conditioning system for EM energy harvesting has also been designed and simulated in TSMC 90 nm CMOS process. The proposed ASIC includes a highly efficient AC-DC converter as well as a power processing unit which steps up and regulates the converted DC voltages using an on-chip DC/DC converter and a sub-threshold voltage regulator with an ultra low power management unit. The total power consumption on the totally passive IC is less than 5 µ
W, which makes it suitable for next generation MEMS-based EM energy harvesters. In the frame of this study, high efficiency CMOS rectifier ICs have been designed and tested together with several vibration based EM energy harvester modules. The results show that the best efficiency and power density values have been achieved with the proposed energy harvesting systems, within the low frequency range, to the best of our knowledge. It is also shown that further improvement of the results is possible with the utilization of a more advanced CMOS technology.

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Silva, Júnior Dalmo Cardoso da. "Modelagem e controle de funções auxiliares em inversores inteligentes para suporte a microrredes CA - simulação em tempo real com controle hardware in the loop". Universidade Federal de Juiz de Fora (UFJF), 2017. https://repositorio.ufjf.br/jspui/handle/ufjf/6511.

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As tecnologias de Geração Distribuída (GD), geralmente, consistem em geradores modulares (em grande maioria renováveis) que oferecem uma série de benefícios poten-ciais, além de estarem mais próximos dos consumidores finais. Embora a GD possa ter colaborações como comentado, a inserção de energias renováveis na rede elétrica pode afetar a proteção e também a estabilidade da mesma, implicando em desvios na tensão e na frequência do sistema. Um dos principais problemas enfrentados é a falta de inér-cia das energias renováveis e também o aparecimento de correntes harmônicas devido às cargas não lineares. Baseado nesse cenário, e como forma de solução dos problemas comentados, surge a pesquisa de inversores multifuncionais, capazes de não só conectar tais energias renováveis à rede elétrica, mas também oferecer suporte a ela. Os serviços ancilares incluem auxílio à estabilidade de tensão e frequência, mitigação de conteúdo harmônico, equilíbrio de geração e demanda de energia, entre outros aspectos. Dessa forma, metodologias baseadas nas implementações alternativas de controle, tais como a Máquina Síncrona Virtual e o Filtro Ativo de Potência (FAP) podem ser adotadas como soluções para esses problemas. Nessa vertente, simulações em tempo real com Hardware In the Loop (HIL) no simulador digital de tempo real (Real Time Digital Simulator) (RTDS) e processamento digital de sinal e engenharia de controle (digi-tal Signal Processing and Control Engineering) (dSPACE), são ferramentas poderosas que podem auxiliar o processo de simulação das funções ancilares analisadas. Assim, nesse trabalho, simulou-se o inversor multifuncional como forma de mostrar a efetiva regulação de tensão, frequência e diminuição do conteúdo harmônico em sistemas de potência, especialmente em microrredes de corrente alternada (CA). Por fim, os resul-tados demonstram o funcionamento do sistema e podem ser usados como validação das estratégias de controle propostas.
Distributed Generation technologies generally consist of modular (mostly renewa-ble) generators that offer a number of potential benefits, while being closer to the end consumers. Although the DG present features as commented, the insertion of renewa-ble energies in the electrical network can affect the protection and also the stability of the network, implying in voltage and frequency deviations. One of the main problems faced is the lack of inertia of renewable energies and also the appearance of harmonic currents due to non-linear loads. Based on this scenario, and as a way of solving these problems, the research of smart inverters, capable of not only connecting such renewable energies to the electric grid but also supporting it, emerges. Some ancillary services as voltage and frequency stability, mitigation of harmonic content, balance of generation and energy demand, among other aspects, can be fullfilled. Thus, methodologies based on sophisticated control implementations such as the Virtual Synchronous Machine and the Active Power Filter, can be adopted as solutions to these problems. In this aspect, real-time simulations with Control Hardware In The Loop HIL in Real Time Digital Simulator RTDS and dSPACE, are a powerfulls tool can aid the simulation process of the analyzed ancillary functions. Thus, in this work, the multifunctional inverter was simulated as a way to show the effective regulation of voltage, frequency, and harmonic content mitigation in power systems, especially in AC microgrids. Finally, the results demonstrate the operation of the system and can be used as validation of the proposed control strategies.

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Martins, Alex de Sá. "Análise e projeto do conversor fonte-y para uso em sistemas de geração de energia fotovoltaica de baixa tensão". Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152334.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Este trabalho aborda o estudo de topologia de conversor de energia baseada no uso de configuração de rede de impedância denominada fonte-Y, com o objetivo de ser aplicado em sistemas de geração distribuída de energia, em redes de baixa tensão. Em sistemas de geração distribuída de energia usualmente se faz necessária a existência de um estágio elevador de tensão e um estágio inversor, ambos controlados para produzir tensão e/ou corrente senoidal com mesma frequência, amplitude e fase da rede elétrica. Nesse sentido, este trabalho propõe a aplicação do conversor fonte- Y entre a geração e a conexão com e rede elétrica, de forma que as ações de conversão relacionadas com a elevação (CC-CC) e inversão (CC-CA) sejam efetuadas de forma integrada por uma única estrutura, contribuindo com a possibilidade de melhoria no rendimento global devido à minimização de estágios de conversão em cascata. Inicialmente, é efetuado um levantamento bibliográfico relacionando as principais topologias de conversores utilizando redes de impedância com indutores acoplados, considerando os aspectos operacionais, arranjo de impedância e ganho estático idealizado, desprezando perdas entre tensão de entrada e tensão máxima de saída obtida. Segue-se o estudo da operação de conversor CCCC empregando rede de impedância do tipo Y, definição das equações que regem o comportamento no tempo das tensões e correntes nos capacitores e indutores. É feita uma avaliação comparativa do ganho estático de tensão obtido e dos esforços nos semicondutores em função das variáveis de controle de projeto e operação disponíveis. Prossegue-se com o estudo da operação do conversor CC-CA empregando rede de impedância do tipo Y, considerando extensão das expressões encontradas para a operação como conversor CC-CC. Por fim, simulações computacionais foram desenvolvidas no ambiente PSIM contemplando o emprego dos circuitos e estratégias de modulação relacionadas com aplicações do conversor fonte- Y, em operação CC-CC e operação CC-CA visando a integração em sistemas de geração de energia, para demonstrar as vantagens e desvantagens do uso dessa topologia.
This paper deals with the study of energy converter topology based on the use of impedance network configuration called Y-source, with the objective of being applied in photovoltaic energy cogeneration systems in low voltage grids. In photovoltaic energy generation systems, it is usually necessary to have a voltage boost stage and an inverter stage, both controlled to produce voltage and / or sine current with the same frequency, amplitude and phase of the power grid. In this sense, this work proposes the application of the Y-source converter between the photovoltaic generation and the connection with the electric grid, so that the conversion actions related to elevation (DC-DC) and inversion (DC-AC) in a way integrated by a single structure, contributing to the possibility of improvement in the overall yield due to the minimization of cascade conversion stages. Initially a bibliographical survey was performed relating the main inverter topologies using impedance networks with coupled inductors considering the operational aspects, impedance arrangement and ideal static gain between the input voltage and the maximum output obtained. ext, the study of the DC-DC converter operation using the Y-type impedance network, definition of the equations governing the time behavior of the voltages and currents in the capacitors and inductors, is presented. It is also done the comparative evaluation of the static voltage gain obtained and the stresses in the semiconductors according to the available control and design control variables. Study of the operation of the DC-AC converter employing type Y impedance network, considering the extension of the expressions found for the operation as DC-DC converter. Finally, computational simulations were developed in the PSIM environment, considering the use of circuits and modulation strategies related to Y-source converter applications, in DC-DC operation and DC-AC operation for integration into power cogeneration systems, to demonstrate advantages and disadvantages of using this topology.
134173/2017-1

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Nathan, Kumaran Saenthan. "A novel DC-DC converter for photovoltaic applications". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288881.

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Growing concerns about climate change have led to the world experiencing an unprecedented push towards renewable energy. Economic drivers and government policies mean that small, distributed forms of generation, like solar photovoltaics, will play a large role in our transition to a clean energy future. In this thesis, a novel DC-DC converter known as the Coupled Inductors Combined Cuk-SEPIC' (CI-CCS) converter is explored, which is particularly attractive for these photovoltaic applications. A topological modification is investigated which provides several benefits, including increased power density, efficiency, and operational advantages for solar energy conversion. The converter, which is based on the combination of the Cuk and SEPIC converters, provides a bipolar output (i.e. both positive and negative voltages). This converter also offers both step-up and step-down capabilities with a continuous input current, and uses only a single, ground-referenced switching device. A significant enhancement to this converter is proposed: magnetic coupling of the converter's three inductors. This can substantially reduce the CI-CCS converter's input current ripple - an important benefit for maximum power point tracking (MPPT) in photovoltaic applications. The effect of this coupling is examined theoretically, and optimisations are performed - both analytically and in simulations - to inform the design of a 4 kW prototype CI-CCS converter, switched at a high frequency (100 kHz) with a silicon carbide (SiC) MOSFET. Simulation and experimental results are then presented to demonstrate the CI-CCS converter's operation and highlight the benefits of coupling its inductors. An efficiency analysis is also undertaken and its sources of losses are quantified. The converter is subsequently integrated into a domestic photovoltaic system to provide a practical demonstration of its suitability for such applications. MPPT is integrated into the CI-CCS DC-DC converter, and a combined half bridge/T-type converter is developed and paired with the CI-CCS converter to form an entirely transformerless single-phase solar energy conversion system. The combination of the CI-CCS converter's bipolar DC output with the combined half bridge/T-type converter's bipolar DC input allows grounding at both the photovoltaic panels and the AC grid's neutral point. This eliminates high frequency common mode voltages from the PV array, which in turn prevents leakage currents. The entire system can be operated in grid-connected mode - where the objective is to maximise power extracted from the photovoltaic system, and is demonstrated in stand-alone mode - where the objective is to match solar generation with the load's power demands.

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49

Agrawal, Ashish, Srikant Kayal y Bhaskar Munshi. "Study of Wind Turbine Driven Doubly Fed Induction Generator (DFIG) Using AC/DC/AC Converter". Thesis, 2009. http://ethesis.nitrkl.ac.in/311/1/studyofDFIG_pdf.pdf.

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In recent years, wind energy has become one of the most important and promising sources of renewable energy, which demands additional transmission capacity and better means of maintaining system reliability. The evolution of technology related to wind systems industry leaded to the development of a generation of variable speed wind turbines that present many advantages compared to the fixed speed wind turbines. These wind energy conversion systems are connected to the grid through Voltage Source Converters (VSC) to make variable speed operation possible. The studied system here is a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG). The stator of the generator is directly connected to the grid while the rotor is connected through a back-to-back converter which is dimensioned to stand only a fraction of the generator rated power. To harness the wind power efficiently the most reliable system in the present era is grid connected doubly fed induction generator. The DFIG brings the advantage of utilizing the turns ratio of the machine, so the converter does not need to be rated for the machine’s full rated power. The rotor side converter (RSC) usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. The additional freedom of reactive power generation by the GSC is usually not used due to the fact that it is more preferable to do so using the RSC. However, within the available current capacity the GSC can be controlled to participate in reactive power generation in steady state as well as during low voltage periods. The GSC can supply the required reactive current very quickly while the RSC passes the current through the machine resulting in a delay. Both converters can be temporarily overloaded, so the DFIG is able to provide a considerable contribution to grid voltage support during short circuit periods. This report deals with the introduction of DFIG, AC/DC/AC converter control and finally the SIMULINK/MATLAB simulation for isolated Induction generator as well as for grid connected Doubly Fed Induction Generator and corresponding results and waveforms are displayed.

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Jun-Hong, Pan y 潘俊宏. "AC/DC Power Conversion Interface for Squirrel-Cage Induction Generator". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/90406197979605325133.

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碩士
崑山科技大學
電機工程研究所
94
The squirrel-cage induction generator has the advantages of rugged construction, simple and reliable operation, less expensive and little maintenance, and it is suitable for small capacity of wind power generation. In this thesis, an AC/DC power conversion interface is developed for the squirrel-cage induction generator used in the wind power generation. The developed power conversion interface is configured by a three-phase rectifier and a three-phase reactive excitation system. The three-phase rectifier is used to convert the AC energy with variable frequency generated form the induction generator to a DC energy, and the DC energy can be supplied to the DC load or converted by a DC/AC inverter to an AC energy with fixed frequency to supply to send to the utility. The functions of three-phase reactive excitation system are to supply the excitation current and filter out the harmonic current. A prototype is established to verify the performance of the proposed power conversion interface for squirrel-cage induction generator. Test results show that the performance of this power conversion interface is excellent.

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