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1
Zhang, Weiyi. „Control of grid connected power converters with grid support functionalities“. Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/456312.
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The installation of power generation systems based on renewable energy sources has been increasing exponentially over the last decades. However, in spite of the well-known merits of such energy sources, the expansion of renewable-based generation (RG) plants, which interface the grid through power converters, can produce also negative impacts on the electrical grid, due to its power processing mechanism, which is different from traditional generation plants. In fact, the regulation capability of the grid can decrease as much as the share of the RG increases. To avoid this, power conversion systems belonging to RG plants are requested to be more grid-friendly, and responsive to the electrical network conditions. In this way, they can contribute to the electrical network stability as other generation does, instead of behaving as simply grid-feeding systems focused on injecting as much power as possible.This PhD dissertation is focused on the control of grid-connected power converters with grid support functionalities based on the Synchronous Power Controller (SPC) concept. The SPC is an established solution for controlling grid connected power converters and equipping them with emulated and improved synchronous machine characteristics. In addition to the general goal of improving the grid interaction of the RG plants, grid support functionality stands as a main property among the characteristics given by the SPC. In this dissertation the virtual admittance structure, contained in the electrical block of the SPC, which emulates the stator output impedance of the synchronous machines, is analyzed. Moreover, it is extended to a study case where the admittance value can be different for positive- and negative-sequence components. The designed virtual admittance block contains three branches, which are responsible for positive-sequence current injection, negative-sequence current injection and other harmonic components, respectively. The converter¿s performance under asymmetrical grid fault is especially considered in this case.The analysis and arrangements in the design of the SPC¿s power loop controller is another contribution of this research. Other methods that consider synchronous machine emulation normally construct the controller by reproducing the synchronous generation swing equation. Based on the virtual implementation, which is free from mechanical constraints, one can set a proper damping factor achieving thus better dynamics compared to the traditional synchronous machines. However, the increase of the damping factor changes the inherent power-frequency (P-f) droop characteristics, which may lead to undesired deviations in the active power generation. In the framework of this PhD, a method that modifies the conventional swing equation emulation and lets the inherent P-f droop characteristics be configurable, independently of the inertia and damping characteristics, is proposed.The work presented in this dissertation is supported by mathematical and simulation analysis. Moreover, in order to endorse the conclusions achieved, a complete experimental validation has been conducted. As it will be shown, the performance of the SPC has been validated in tests once the main parts, namely virtual admittance and power loop controller, and other parts are settled. The simulation and experimental test scenarios include events like changes in the power operation point, frequency sweeps, voltage magnitude changes, start-up and parallel converters operation, which are given under different control configurations like the different structures for the power loop controller and different control parameters. This PhD research also compares the transient performance of the SPC-based power converters with the ones achieved with conventional control methods.Los convertidores de potencia conectados a la red actúan comúnmente como interfaz entre plantas de generación basadas en energía renovable y la red eléctrica, permitiendo así el procesado de energía eólica y fotovoltaica y su inyección a red. El control de estos convertidores conectados a la red ha sido objeto de estudio en las últimas décadas, ya que su comportamiento y prestaciones influye de forma determinante tanto en la calidad de la red eléctrica, así como en el cumplimiento de los requisitos de conexión a la red fijados por los códigos de red. Junto con la expansión de las plantas de generación de energía renovable, su impacto en el sistema eléctrico ha crecido también, lo cual ha hecho que se lleven a cabo muchos trabajos de investigación orientados a armonizar la penetración de renovables con la estabilidad de la red. Con los sistemas de control actuales la capacidad de regulación de la red disminuye tanto como la proporción de la generación renovable aumenta. En las redes eléctricas del futuro, se espera que los convertidores de potencia, que actúan como interfaz, exploten sus posibilidades de cómputo y control permitiendo mejorar la interacción de la generación renovable con la red. En este contexto los controles de tipo “droop control”, los cuales son ampliamente utilizados en sistemas de generación tradicionales, se pueden aplicar a los convertidores conectados a red para habilitar funciones de soporte de red, ya que estos contribuyen al control de tensión y frecuencia primaria ajustando el intercambio de potencia activo y reactiva de forma proporcional a la desviación de la frecuencia y magnitud de la tensión en el punto de conexión. En el caso de regulación de frecuencia, y para que este sea bidireccional, el convertidor puede interactuar con la red con la ayuda de sistemas de almacenamiento de energía. Sin embargo, la inclusión del “droop control” no conlleva una solución global. Incluso si se ajusta de forma óptima y se dispone de reserva de energía, aún hay cuestiones como la respuesta inercial que no se pueden dar con este tipo de control. La generación en los sistemas tradicionales se lleva a cabo principalmente por generadores síncronos. Comparados con estos, los convertidores conectados a la red difieren principalmente en la falta de la característica electromecánica. En consecuencia, la estática y la dinámica de las unidades de generación de energía renovable son diferentes en comparación con los generadores síncronos. La dinámica de estos convertidores es altamente dependiente de los sistemas de sincronización (PLL), cuyo comportamiento se degrada en condiciones de red adversas o distorsionadas. Además, el control de potencia normalmente depende control de potencia instantáneo. Debido a las diferentes dinámicas, la inercia total en la red no aumenta junto con la integración de las energías renovables. Sin embargo, los códigos de red han incluido requerimientos tales como “inercia sintética" en los requisitos. Otras deficiencias del control del convertidor convencional incluyen el rendimiento inferior bajo condiciones de avería de red, en conexión de red débil y conexión de red de relación X / R baja. Esta tesis doctoral estudia y valida el control de los convertidores conectados a la red con funcionalidades de soporte de red. El objetivo general del trabajo es mejorar las características de interacción de la red de las plantas de generación de energía renovable mediante la especificación de los convertidores conectados a la red con características de la máquina síncrona emulada y mejorada. La tesis ha aportado contribuciones o ha mostrado originalidades en los siguientes aspectos: Un enfoque de ajuste de bucle de control de corriente interno generalizado; Diseño detallado y validación de la admisión virtual para convertidores conectados a la red; Diseño detallado y validación del circuito de control de potencia para la emulación de inercia y amortiguación.
2
Roos, Pontus. „A Comparison of Grid-Forming and Grid-Following Control of VSCs“. Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413872.
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Variable renewable energy sources are today increasingly integrated in the power system as a step towards the renewable society. The large-scale introduction of converter-based energy sources brings challenges in terms of reduced damping to the power system due to the reduced number of synchronous generators. This can be manifested as high rate-of-change-of-frequency and decreased grid stability. To forestall this reduced performance, it is suggested that the grid-following control of today’s converters are restructured to a grid-forming control, enabling the converter to behave closer to a synchronous machine. This thesis compares grid-following and grid-forming control and seeks to further describe this grid-forming behavior by applying a grid-forming control method on an energy storage enhanced STATCOM-system. A continuous time model and a linearized model based on state space representations are constructed in order to investigate the grid-forming behavior but also how the converter stability is affected by a restructure from grid-following to grid-forming control. The results indicate that the investigated grid-forming control method displays a behavior similar to synchronous machines and incorporates the ability to provide frequency response services and so called “synthetic inertia” to the grid. The results also show that the stability of the converter (the ability to provide a bounded output when the system is perturbed) is ensured when the control method is restructured from grid-following to grid-forming and that the investigated grid-forming method is stable also in weak grid situations.
3
Wu, Yifan. „Grid-forming Inverter Control for Improving Power System Stability“. Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/27492.
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Renewable energy sources are being widely adopted by more and more countries due to their comparatively low cost, flexibility, and environmental benefits. Grid-forming control is becoming an important technology to address the stability issues resulting from the retirement of conventional synchronous generation. Unlike conventional grid-following inverters, predominantly used today for the connection of wind and solar farms, grid-forming inverters behave much like synchronous machines by providing both inertia and system strength. Against this backdrop, this thesis investigates the problem of designing grid-forming inverter control algorithms for the utility-scale battery storage system, focusing on power system applications specifically. Firstly, we investigated the theory of grid-tied inverter control strategies. Then we mathematically modelled the voltage source converter (VSC) system and used DIgSILENT PowerFactory to conduct several case studies. For the first case study, a four-bus test system was modelled, which then served as a benchmark system to test the system-level control strategies for the grid-tied inverter. The crucial role of the grid-forming control in supporting system inertia and system strength was revealed. Furthermore, we proposed a stability scanning framework to help system planners determine the amount and location of utility-scale battery storage equipped with grid-forming inverters. Afterwards, we used a simplified model of the Australian NEM as another case study. We performed time-series scanning with an hourly resolution to capture the intraday and interseasonal variation in the output of variable renewable generation. The results demonstrated that grid-forming control could markedly improve the frequency performance of power systems dominated by converter-interfaced renewable generation.
4
Alfares, Abdulgafor Mohammed. „Analysis of power converter's control techniques in Grid-Tie and AC Micro/Smart Grid“. Thesis, Marquette University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1553890.
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Power converters have an outstanding potential in micro and smart grid applications that require flexible and fast power control as well as rigid voltage regulation at the point of common coupling. Power converters are required to properly operate under several modes of operation such as grid-tie and micro-grid modes of operations. In addition, the control system should be designed to enable proper load sharing between several units.
Several control techniques have been proposed in the literature to address most of the control requirements of the power converters under different operating modes mentioned above. However, references found in the literatures are usually centered on the analysis of the system under only one mode of operation and using a single control strategy. Comprehensive study that combines an in depth analysis of the power converters control under several modes are very scarce in the literature.
In this thesis, a detailed survey and analysis of power converter control techniques in Grid-Tie and AC Micro/Smart Grid applications are introduced. This analysis is based on detailed nonlinear time domain simulations as well as average and small signal models for system stability assessment and performance evaluation.
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Das, Debrup. „Dynamic control of grid power flow using controllable network transformers“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43739.
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The objective of the research is to develop a cost-effective, dynamic grid controller called the controllable network transformer (CNT) that can be implemented by augmenting existing load tap changing (LTC) transformers with an AC-AC converter. The concept is based on using a fractionally rated direct AC-AC converter to control the power through an existing passive LTC. By using a modulation strategy based on virtual quadrature sources (VQS), it is possible to control both the magnitude and the phase angle of the output voltage of the CNT without having any inter-phase connections. The CNT architecture has many advantages over existing power flow controllers, like absence of low frequency storage, fractional converter rating, retro-fitting existing assets and independent per-phase operation making it potentially attractive for utility applications.
The independent control of the magnitude and the phase angle of the output voltage allow independent real and reactive power flow control through the CNT-controlled line. In a meshed network with asymmetric network stresses this functionality can be used to redirect power from critically loaded assets to other relatively under-utilized parallel paths. The power flow controllability of CNT can thus be used to lower the overall cost of generation of power. The solid state switches in the CNT with fast response capability enable incorporation of various additional critical functionalities like grid fault ride through, bypassing internal faults and dynamic damping. This bouquet of features makes the CNT useful under both steady state and transient conditions without compromising the grid reliability.
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Aminou, Moussavou Anges Akim. „Modelling and analysis of microgrid control techniques for grid stabilisation“. Thesis, Cape Peninsula University of Technology, 2014. http://hdl.handle.net/20.500.11838/1184.
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Thesis submitted in fulfilment of the requirements for the degree
Master of Technology: Electrical Engineering
in the Faculty of Engineering
at the
Cape Peninsula University of Technology
2014In recent times, renewable energy-based distributed generation (DG) has captivated the industrial sector and on a global scale this has become a leading research area. Distributed generation using wind, solar energy or biomass as a source of energy can produce electricity on a small scale. Therefore, there is a strong focus on using renewable energy as a safe alternative source of energy, especially because it can in future play a dominant role in the world’s energy production and help to tackle the increase of global warming caused by fossil energy. However, a major problem facing renewable energies is that they are highly dependent on weather conditions. Since the power generated by DG, as well as consumption, depends on the weather conditions, irregularity of production and consumption leads to frequency and voltage fluctuations, and it can become difficult to determine and monitor consumer usage at any given time. Distributed generation can then be subjected to discrepancies in consumer usage and this can lead to severe overloading. As a result, microgrids powered by DG, operating in a single, stand-alone controllable system mode, face new challenges in terms of balancing a cluster of loads. Balancing a cluster of loads by making sure at all times that the entire system operates without overloading, is an essential requirement for the proper operation of a power system. The microgrid load considered in this project is the sum of sensitive and non-sensitive loads, respectively 5 kW and 100 kW, which constitute load requirement of one village; this total load required by a number of villages is called a cluster load. Depending on the input power generated by a DG-based photovoltaic (PV) system, these loads can be controlled using a logic control switch (LCS). When the power produced is less than the minimum load required by a component of a cluster, overloading occurs. The purpose of using an LCS is to ensure that a stable system is maintained under various loads and resource conditions. An LCS is used to continuously monitor and adjust load through circuit breakers. It is a good alternative to load balancing for a cluster of villages in rural area where a microgrid is operating in stand-alone mode. The focus of this research is to design a photovoltaic system with a maximum capacity of 1 MW providing power to a cluster of rural villages, and operating in stand-alone mode, and then to apply different control techniques (droop control, dq0 reference frame + proportional integral (PI) controller, and PI controller alone) at the inverter terminal of the PV system, in order to evaluate the stability of the output voltage. Another goal of the research is to develop an energy management system (EMS) algorithm to support the PV system in reducing loads. Therefore, a iii stable system under various load and resource conditions, as well as suitable control mechanisms are required to model a PV system. There is a need for the modelling of a PV array using a physical modelling block in MATLAB (SIMULINK) software. The state flow provided by SIMULINK is used in this project to develop an algorithm for load balancing. The state flow gives possibilities of modelling complex algorithms by combining graphical and tabular representations to create sequential decision logic, derived from state transition diagrams and tables, flow charts and truth tables. Furthermore, the design of a microgrid using photovoltaic DG and an energy management system, has been developed. The present work mainly consists of a stand-alone microgrid operation, where the power generated must be equal to the load power. In addition, different control methods, consisting of a dq0 reference frame + PI controller, are analysed at the invertor terminal. Subsequently an LCS algorithm is developed; this is required to maintain the system within certain limits and prevents overloading. LCS algorithms are based on a flowchart and allow switching automatically selected loads, depending on the power (solar radiation) available. In addition, a flow chart provides an easy way of using a graphical transition state and state chart to establish a set of rules for the system. The simulation results show that both droop control and a dq0 reference frame + PI controller are much better than a PI controller alone; these results also compared well with similar studies found in the literature. Also, these results are further improved with an EMS in order to maintain the output voltage of the microgrid, by switching on and off certain loads depending on the input power. The modelling of the microgrid using DG, based on photovoltaic systems with a maximum capacity of 1 MW, supports and improves the PV system by reducing loads. Moreover, droop control, and dq0 transformation + PI control present a better result than PI controller alone.
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Ghias, Nezhad Omran Nima. „Power grid planning for vehicular demand: forecasting and decentralized control“. IEEE Transactions on Smart Grid, 2014. http://hdl.handle.net/1993/23891.
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Temporal and spatial distribution of incoming vehicular charging demand is a significant challenge for the future planning of power systems. In this thesis the vehicular loading is-sue is categorized into two classes of stationary and mobile; they are then addressed in two phases.
The mobile vehicular load is investigated first; a location-based forecasting algorithm for the charging demand of plug-in electric vehicles at potential off-home charging stations is proposed and implemented for real-world case-studies. The result of this part of the re-search is essential to realize the scale of fortification required for a power grid to handle vehicular charging demand at public charging stations.
In the second phase of the thesis, a novel decentralized control strategy for scheduling vehicular charging demand at residential distribution networks is developed. The per-formance of the proposed algorithm is then evaluated on a sample test feeder employing real-world driving data. The proposed charging scheduling algorithm will significantly postpone the necessity for upgrading the assets of the network while effectively fulfilling customers’ transportation requirements and preferences.October 2014
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Su, Po-An (Po-An Leo). „Demonstration of HVAC chiller control for power grid frequency regulation“. Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99306.
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Thesis: S.M. in Building Technology, Massachusetts Institute of Technology, Department of Architecture, 2015.Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 74-77).
Secondary frequency regulation is a necessary electric grid ancillary service that balances electric power system supply and demand on short time intervals of seconds to minutes. Commercial HVAC chillers may be well positioned to provide secondary frequency regulation as a demand side resource. Commercial 200 ton (703 kWth) chillers serving two buildings in the Boston area are used to experimentally develop a practical closed-loop controller that modifies chiller power demand to provide secondary frequency regulation. In the first setup, a physical controller is connected directly to the chiller and adjusts power through chilled water setpoint. In the second setup, both the chiller and air handling units are controlled through the BAS. Demonstrations using standard electric system operator test routines show the chiller power response to exceed qualification requirements while providing up to +/-25% of chiller nameplate power in secondary frequency regulation capability. The controller is further demonstrated to provide secondary frequency regulation continuously for several hours longer than the standard test routines, during which building cooling load changes significantly. Analysis of results indicate minimum power and variable COP as two factors that could be incorporated into future models to more accurately reflect observed chiller transient behaviour and predict performance. BAS communication delays, ramp rate limits, and compressor cycling are additional factors that can have significant negative impacts on controller performance. Extrapolation of experiment results to higher-level analysis indicates that chillers can contribute to the secondary frequency regulation requirements at the grid level in aggregate, although potential varies greatly depending on climate and building type. There is more potential in the south, where 21% of secondary frequency regulation requirements might be met with chillers; the contribution of chillers in colder climates is minimal. Short-term power balance to achieve stability is essential for the operation of the modern electrical power system. Providing stability through modified control of existing HVAC chillers in commercial buildings is a technologically feasible alternative to existing solutions and can make a meaningful contribution to the electrical grid.
by Po-An (Leo) Su.
S.M. in Building Technology
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Jupin, Samuel. „Advanced Control of Multilevel Power Converters for Weak Grid Applications“. Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0210.
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Avec l’avènement des micros-réseaux incorporant les sources d’énergie renouvelable, un nouveau paradigme apparaît dans la distribution de l’électricité. Ces nouvelles architectures interfacent des consommateurs non contrôlés à des sources d’énergie intermittentes, plaçant de fortes contraintes sur les étapes de conversion, stockage et gestion de l’énergie.Les convertisseurs de puissance s’adaptent avec en particulier le développement des convertisseurs multiniveaux, qui supportent à composants égaux des puissances plus importantes que leurs prédécesseurs et assurent une meilleure qualité de l’énergie, mais dont le contrôle gagne en complexité.Du fait de leur nature hybride, le contrôle des convertisseurs de puissance est traditionnellement scindé en deux parties. D’un côté les objectifs continus liés à la fonction principale d’interfaçage des convertisseurs, de l’autre le pilotage des interrupteurs quantifiés qui le forment, la modulation.Dans ce contexte, les exigences croissantes en rendement, fiabilité, polyvalence et performance imposent un gain conséquent d’intelligence de l’ensemble de l’architecture de contrôle. Pour répondre à ces exigences, nous proposons de traiter à la fois les objectifs liés à la fonction d’interface des convertisseurs et ceux rattachés à leur nature avec un unique contrôleur. Cette décision implique d’incorporer la non-linéarité des convertisseurs de puissance au contrôleur. Une approche de Contrôle à Modèle Prédictif (MPC) a été retenue pour traiter cette non-linéarité ainsi que la diversité d’objectifs de contrôle qui accompagne les convertisseurs.L’algorithme développé combine la théorie des graphes, avec divers algorithmes comme ceux de Dijkstra et A* à un modèle d’état spécialisé pour les systèmes à commutation, formant ainsi un outil puissant et universel capable de manipuler et la nature discrète des interrupteurs de puissance et celle continue de son environnement. L’étude du modèle d’état utilisé pour les convertisseurs de puissance comme systèmes commutants conduit à des résultats concernant la stabilité et la contrôlabilité de ces systèmes.Le contrôleur obtenu est éprouvé en simulation, face à des cas d’applications variés : onduleur isolé ou connecté à un réseau, redresseur et convertisseur bidirectionnel. La même structure de contrôle est confrontée à chacune de ces situations pour trois topologies multi-niveaux : Neutral Point-Clamped, Flying Capacitor et Cascaded H-Bridge. La capacité d’adaptation du contrôleur est regroupée dans deux étapes : la prédiction, qui utilise le modèle du convertisseur, et la fonction de coût, qui traduit le cahier des charges en un problème d’optimisation résolu par l’algorithme. Changer de topologie implique de modifier le modèle, sans impact sur la fonction de coût, tandis que modifier cette fonction suffit à s’adapter aux différentes applications.Les résultats montrent que le contrôleur pilote directement les interrupteurs de puissance en fonction des objectifs. Les performances générales de cette structure unique sont comparables à celles des structures multiples utilisées pour chacun des cas étudiés, à l’exception notable du fonctionnement redresseur, où la rapidité et l’étendue des possibilités sont tout particulièrement intéressants.En conclusion, le contrôleur développé est capable de traiter un grand nombre d’applications, topologies, objectifs et contraintes. Alors que les modifications du cahier des charges ou des conditions de fonctionnement impactent souvent profondément les structures de contrôle linéaire, ces altérations ne modifient pas l’architecture du contrôleur MPC développé. Cela illustre la polyvalence de la solution proposée ainsi que son universalité, démontrée davantage par la capacité à s’adapter à des convertisseurs de puissance différents et sans modifications. Finalement, la complexité de la modulation est toute incluse dans la structure, offrant un gain de simplicité et de flexibilité au design du contrôleWith the progressive rise of the micro-grids incorporating renewable energy sources, a new electricity distribution paradigm is emerging. These new architectures interface uncontrolled consumers with intermittent energy sources, therefore imposing more stress on the conversion, storage and management of the energy.Power converters are adapting accordingly, in particular, with the development of multi-level converters, which allow higher power rates and better power quality than their predecessors with similar components, but whose control is becoming increasingly complex.Due to their hybrid nature, the control of power converters is traditionally split into two parts: on the one side, the continuous objectives related to the main interfacing function of the power converters, and, on the other side, the driving of their quantized power switches, known as the modulation strategy.In this context, the growing demands in efficiency, reliability, versatility and performance require a high level of intelligence of the complete control structure. To meet these requirements, the objectives of this research work are to address both the interfacing objectives and the inner driving of the converter into a single controller. This decision implies incorporating the non-linearity of power converters into the controller, equivalent to suppressing the traditional modulation block. Modulation is the traditional solution to linearize the inner operation of the converters. The Model Predictive Control (MPC) approach was chosen to handle the non-linearity and the diversity of control objectives that accompany power converters.The developed control algorithm combines graph theory, with Dijkstra, A* and other algorithms, with a special state-space model designed for switching systems to form a powerful universal tool capable of simultaneously manipulating the discrete and continuous nature of the converter and its environment. Switched state-space models are studied, leading to interesting results on stability and controllability concerning their application on power converters.The obtained controller is then tested in simulation, with various case studies: grid-connected and standalone inverter, rectifier and bidirectional operation. These situations are studied for three common multi-level topologies: Neutral Point-Clamped, Flying Capacitor and Cascaded H-Bridge. The exact same MPC structure is used for each and every one of the case studies, with adaptations of its internal behavior. This behavior is agglomerated in two functions: the prediction, containing the model of the converter, and the cost function, which translates the control requirements into the optimal problem solved by the algorithm. Changing the topology implies adjusting the model, without impacting the cost function, while modifying this function is sufficient to adapt to the different applications.The results show that the controller manages to directly drive the power switches according to the application, demonstrating a large variety of considerations and objectives. The overall performance of this unique structure is comparable to that of the multiple structures used for each of the studied cases, with the notable exception of rectifier operation mode, where the speed and range of possibilities are particularly interesting.In conclusion, the developed controller manages miscellaneous applications, topologies, objectives and constraints. While the traditional linear control structures have to change, often deeply, for different operation modes and control requirements, such modifications do not affect the control architecture of the designed MPC controller. This shows the versatility of the proposed solution and its universality, further demonstrated by its ability to adapt to different power converters without modifications. Finally, the complexity of the modulation is fully included in the structure, offering simplicity and flexibility to the control design
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McAndrew, Thomas Charles. „Weighted Networks: Applications from Power grid construction to crowd control“. ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/668.
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Since their discovery in the 1950's by Erdos and Renyi, network theory (the study of objects and their associations) has blossomed into a full-fledged branch of mathematics.
Due to the network's flexibility, diverse scientific problems can be reformulated as networks and studied using a common set of tools.
I define a network G = (V,E) composed of two parts: (i) the set of objects V, called nodes, and (ii) set of relationships (associations) E, called links, that connect objects in V.
We can extend the classic network of nodes and links by describing the intensity of these associations with weights.
More formally, weighted networks augment the classic network with a function f(e) from links to the real line, uncovering powerful ways to model real-world applications.
This thesis studies new ways to construct robust micro powergrids, mine people's perceptions of causality on a social network, and proposes a new way to analyze crowdsourcing all in the context of the weighted network model.
The current state of Earth's ecosystem and intensifying climate calls on scientists to find new ways to harvest clean affordable energy.
A microgrid, or neighborhood-scale powergrid built using renewable energy sources attached to personal homes, suggest one way to ameliorate this energy crisis.
We can study the stability (robustness) of such a small-scale system with weighted networks.
A novel use of weighted networks and percolation theory guides the safe and efficient construction of power lines (links, E) connecting a small set of houses (nodes, V) to one another and weights each power line by the distance between houses.
This new look at the robustness of microgrid structures calls into question the efficacy of the traditional utility.
The next study uses the twitter social network to compare and contrast causal language from everyday conversation.
Collecting a set of 1 million tweets, we find a set of words (unigrams), parts of speech, named entities, and sentiment signal the use of informal causal language.
Breaking a problem difficult for a computer to solve into many parts and distributing these tasks to a group of humans to solve is called Crowdsourcing.
My final project asks volunteers to 'reply' to questions asked of them and 'supply' novel questions for others to answer.
I model this 'reply and supply' framework as a dynamic weighted network, proposing new theories about this network's behavior and how to steer it toward worthy goals.
This thesis demonstrates novel uses of, enhances the current scientific literature on, and presents novel methodology for, weighted networks.
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Gautam, Samir. „Synchronization and Control of Grid Connected Single-Phase Power Converter“. Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/25807.
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The adoption of power converters has thrived in electric loads, distributed generation, utility, and electric vehicles for their role in efficient energy conversion. However, interfacing these nonlinear power electronics based devices to the power system has triggered a rise in the harmonic distortion level. Grid overvoltage is another issue attributable to the deepening penetration of distributed generation such as rooftop PV systems in the distribution network. To address these power quality concerns, power converters offer the most effective solution. One such application is the active power filter (APF) which can accomplish fast and flexible power quality compensation. Synchronization and control system remains an indispensable part for the effective operation of APF or any grid interfaced power quality compensator. The performance of APF essentially depends on the dynamics and accuracy of two subsystems: grid synchronization and the reference current extraction (RCE).
The RCE is basis to the operation of APF and responsible for computing the compensation current. The aim is to extract the fundamental/harmonics component fast and accurately. Among numerous solutions, RCE based on dq/synchronous reference frame (SRF) transformation is advantageous for its simplicity, efficacy, and clarity in selective harmonic extraction. It necessitates orthogonal signal generation (OSG) unit and synchronization signal (from synchronization unit) both of which remain vital to its working. Deploying transfer delay (TD) as OSG in RCE application has been restrained by the deficiency of harmonic filtering and adversity in adapting to grid frequency. Synchronization is an act of acquiring details of the grid (phase, frequency, and amplitude), to assure the power converter works in harmony with the utility grid. Among several synchronization techniques, phase locked loop (PLL) based on OSG has been widely embraced for single-phase electric power applications. Despite offering a simpler implementation, transfer delay (TD) and all-pass filter (AF) built OSG-PLLs have found limited applications in literature. Two main challenges facing these PLLs are the degraded performance in abnormal grid voltage (i.e distortion and presence of dc offset) and adaption of OSG units to variations in grid frequency.
In this dissertation, some contributions are made to TD-RCE and two state-of-the-art PLLs (belonging to family of OSG-PLL): transfer delay (TD) and all-pass filter (AF). This thesis demonstrates that through systematic and optimal design, TD-RCE can be competitive with other advanced methodologies reported in the literature. In this context, an enhanced TD-RCE is proposed with faster transient and higher steady state accuracy even in off-nominal frequency. Regarding TD-PLL, first, the use of arbitrary delay length to further enhance the dynamic performance is proposed via dual-loop PLL system. Secondly, to improve the accuracy of grid parameter estimation in abnormal grid scenarios, an efficient inloop filtering method with the least impact on PLL dynamics is presented. Concerning AF-PLL, first, four topologies of frequency-fixed AF-PLLs are developed to eliminate the frequency feedback loop (to OSG) to simplify the control and stability analysis. Secondly, to boost the filtering capability, an efficient integration of prefilter before the AF-PLL structure is recommended.
Lastly, this thesis recommends an alternative solution to address the overvoltage problem in low voltage distribution systems. A typical response to mitigate the voltage rise problem involves reactive power control, which if inadequate, is followed by active power curtailment of distributed generation. Instead of having a separate power quality compensator (such as APF), the possibility of employing electric home appliances for ancillary services is recommended. However, in the current configuration, the grid support capabilities of residential electrical loads are sparse and limited. This thesis first formulates the required modification in appliance topology and control to enable wider reactive power support (RPS) capability. Then, the framework assisting the realization of RPS from electrical home appliances is devised. Finally, the financial benefit of this strategy is justified by economic assessment.
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Jain, Chinmay. „Design, control and implementation of grid tied solar energy conversion systems“. Thesis, IIT Delhi, 2017. http://localhost:8080/xmlui/handle/12345678/7058.
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Athanasius, Germane Information Technology & Electrical Engineering Australian Defence Force Academy UNSW. „Robust decentralised output feedback control of interconnected grid system“. Awarded by:University of New South Wales - Australian Defence Force Academy, 2008. http://handle.unsw.edu.au/1959.4/39591.
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The novel contribution of the thesis is the design and implementation of decentralised output feedback power system controllers for power oscillation damping (POD) over the entire operating regime of the power system. The POD controllers are designed for the linearised models of the nonlinear power system dynamics. The linearised models are combined and treated as parameter varying switched systems. The thesis contains novel results for the controller design, bumpless switching and stability analysis of such switched systems. Use of switched controllers against the present trend of having single controller helps to reduce the conservatism and to increase the uncertainty handling capability of the power system controller design. Minimax-LQG control design method is used for the controller design. Minimax-LQG control combines the advantages of both LQG and H control methods with respect to robustness and the inclusion of uncertainty and noise in the controller design. Also, minimax-LQG control allows the use of multiple integral quadratic constraints to bound the different types of uncertainties in the power system application. During switching between controllers, switching stability of the system is guaranteed by constraining the minimum time between two consecutive switchings. An expression is developed to compute the minimum time required between switchings including the effect of jumps in the states. Bumpless switching scheme is used to minimise the switching transients which occur when the controllers are switched. Another contribution of the thesis is to include the effect of on load tap changing transformers in the power system controller design. A simplified power system model linking generator and tap changing transformer dynamics is developed for this purpose and included in the controller design. The performance of the proposed linear controllers are validated by nonlinear computer simulations and through real time digital simulations. The designed controllers improve power system damping and provide uniform performance over the entire operating regime of the generator.
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Gao, Shuang, und 高爽. „Design, analysis and control of vehicle-to-grid services“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/197100.
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There are unique challenges and opportunities related to the integration of electric vehicles into the future power grid, especially the modern distribution grid since electric vehicle (EV) charging facilities and fast-charging stations are usually tied to low-voltage and medium-voltage power networks. The grid-connected EVs, if properly controlled, can operate as distributed energy storage and provide various ancillary services, such as peak shaving, fast-response reserve capacity, frequency regulation, voltage control and reactive supports.
The purpose of this thesis is to integrate EVs to the power grid and provides suitable ancillary services to improve the grid reliability and stability. The larger future penetration of EVs and renewable energies is also taken into account to develop the vehicle-to-grid (V2G) control scheme with the constraints of EV charging and communication infrastructures. The main contents include: V2G mathematical model and system configuration; impact evaluation of EV integration and the V2G control framework; energy scheduling of EVs integration; V2G dynamic regulation services; control method of EV aggregator for dispatching a fleet of EVs; and the evaluation of V2G control scheme and hardware-in-the-loop experimental system design.
In the thesis, the impact of EV charging demand on the conventional distribution grid is firstly estimated to reveal the negative effects of the arbitrary EV charging and the necessity to control the EV charging process. The potential benefits EVs can bring into the power grid support are discussed and a V2G control framework is proposed to perform the V2G optimization and various regulation services. The current power electronics applied EV charging facilities and communication network are integrated into the V2G operation in the future distribution grid with microgrid and smaller installation of renewable generation units.
Next, mathematical model of V2G power control is formulated. Two optimization methods are proposed to schedule the EV charging and discharging energy to minimize the power losses and the operating cost while satisfying the mobility needs and the power system limitations. Subsequently, the dynamic regulation of V2G power is investigated to unleash the potential of EVs to provide multiple ancillary services simultaneously. In addition to V2G optimal energy scheduling, EVs can also be employed for dynamic power regulation which requires the fast response to the instantaneous imbalance between the power supply and demand. V2G power is controlled to mitigate the power fluctuation caused by the intermittent wind energy resources, and thus stabilize the system frequency and voltage.
Finally, an EV-centric hybrid energy storage system is proposed, which combines the merits of V2G operation and superconducting magnetic energy storage (SMES) to enhance the power quality and system frequency stability. The critical issues in V2G applications are summarized in the end.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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Villemin, Maxime. „Alarm handling in the control room of a Nuclear Power Plant“. Thesis, KTH, Fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92111.
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Luo, Gang. „Development of a Digital Desk for Power Plant Control Room Operators“. Thesis, Linköpings universitet, Institutionen för datavetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-62353.
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Multi-touch technology and digital tabletops have been used in different fields. They provide a natural way of interaction with computers through gestures. In this report, we present a digital desk for power plant control rooms aimed at visualizing the power grid status. The thesis reports about the development of this desk that comprised field studies, use cases and requirements identification, low fidelity prototyping, and software development. A final evaluation of the design indicated that digital tabletops can be valuable for control room operators since they can enhance learning and communication among the collaborating operators. The work was done at ABB Corporate Research in Sweden.
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Alshogeathri, Ali Mofleh Ali. „Vehicle-to-Grid (V2G) integration with the power grid using a fuzzy logic controller“. Thesis, Kansas State University, 2015. http://hdl.handle.net/2097/20606.
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Master of ScienceDepartment of Electrical and Computer Engineering
Shelli K. Starrett
This thesis introduces a Vehicle to Grid (V2G) system which coordinates the charging, and discharging among the Electric Vehicles (EVs) and two-test systems, to help with peak power shaving and voltage stability of the system. Allowing EVs to charge and discharge without any control may lead to voltage variations and disturbance to the grid, but if the charging and discharging of the EVs is done in a smart manner, they can help the power network. In this thesis, fuzzy logic controllers (FLC) are used to control the flow of power between the grid and the electric vehicles. The presented work in this thesis mainly focuses on the control architecture for a V2G station that allows for using EVs batteries to help the grid’s voltage stability. The designed controllers sustain the node voltage, and thus also achieve peak shaving. The proposed architectures are tested on 16 -generator and 6-generator test systems to examine the effectiveness of the proposed designs. Five fuzzy logic schemes are tested to illustrate the V2G system’s ability to influence system voltage stability. The major contributions of this thesis are as follows: • FLC based control tool for V2G station present at a weak bus in the system. • Investigate the effect of the station location and voltage sensitivity. • Comparison of chargers providing real power versus reactive power. • Simulation of controller and system interactions in a daily load curve cycle. Keywords: State of Charge (SOC), Electric Vehicle (EV), Fuzzy Logic Controller (FLC), Vehicle to grid (V2G), and Power System Voltage Stability.
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Arif, Bilal. „Real-time grid parameter estimation methods using model based predictive control for grid-connected converters“. Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31963/.
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In recent years, renewable and distributed generation (DG) systems have contributed towards an efficient and an economic way of transporting electricity to end-users as the generation sources are in general located nearer the loads. DG and renewable energy systems are modifying the old concept of distribution network by instigating a bi-directional power flow into the grid, facilitated through the use of power electronic grid-connected converters. A challenge associated with grid-connected converters arises when they are interacted with a grid that is not stiff, like weak micro grids. Small grid parameter variations in these systems can considerably affect the performance of the converter control and lead to higher values in current total harmonic distortion (THD) and loss of control and synchronization. Thus, the control of grid-connected power converters needs to be regularly updated with latest variation in grid parameters. Model Predictive Direct Power Control (MP-DPC) has been chosen as the control strategy for the work presented in this thesis due to its advantages over traditional control techniques such as multivariable control, no need of phase-locked loops (PLLs) for grid synchronization and avoidance of cascaded control loops. Two novel methods for estimating the grid impedance variation, and hence the grid voltage, are presented in this thesis along with a detailed literature review on control of grid-connected converters with special emphasis on impedance estimation techniques. The first proposed estimation method is based on the difference in grid voltage magnitudes at two consecutive sampling instants while the second method is based on a model-fitting algorithm similar to the concept of cost-function optimization in model predictive control. The proposed estimation methods in this thesis are integrated within the MP-DPC, therefore updating the MP-DPC in real-time with the latest variation in grid impedance. The proposed algorithms provide benefits such as: quick response to transient variations, operation under low values of short-circuit-ratio (SCR), robust MP-DPC control, good reference tracking to grid parameter variations and operation under unbalanced grid voltages. The thesis also presents the advantages and drawbacks of the proposed methods and areas where further improvement can be researched. The work presented has been tested on a three phase two-level grid-connected converter prototype, which is connected to a low voltage substation highly dominated by inductive component of grid impedance. It can be adapted and modified to be used for general grid impedance estimation, medium or high voltage applications, in case of multilevel grid-connected converter topologies or photo-voltaic (PV) grid-connected applications.
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Wang, Zhongkui. „Reactive Power Control and Optimization of Large Scale Grid Connected Photovoltaic Systems in the Smart Grid“. The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1388764166.
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Hannisdal, Erik Lundegaard. „Optimal Voltage Control of the Southern Norwegian Power Grid : Mixed Integer Nonlinear Programming (MINLP) for Control and Optimization of the High Voltage Southern Norwegian Power Grid“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for teknisk kybernetikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13180.
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This thesis contains the synthesis, analysis and simulation results of an automatic optimal voltage controller for the Southern Norwegian power grid. Currently the high voltage power grid is controlled manually by operators switching control components. The optimal controller handles the voltage control of the system, as well as keeping the number of control actions to a minimum.The system model is derived from power system analysis. Due to a highy nonlinear system model and integer decission variables in on/off control components, the controller is based on mixed integer nonlinear programming (MINLP). The MINLP uses BONMIN as a solver, and is implemented with the AMPL programming language.It was found that a MINLP controller is good choice for voltage control in transmission systems. The controller handles voltage limits, as well as reducing the number of control actions.The thesis also contains comparison between different solution methods for applying the optimal voltage controller, as well as other approaches to the automatic voltage control problem.
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Mataifa, Haltor. „Modeling and control of a dual-mode grid-integrated renewable energy system“. Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2190.
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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2015.From the electric power generation perspective, the last three decades have been characterized by sustained growth in the amount of Distributed Power Generation (DPG) systems integrated into the electric grid. This trend is anticipated to continue, especially in light of the widespread acceptance of the many benefits envisaged in the increase of renewable-based power generation. The potential for grid-integrated DPG systems to significantly contribute to electric power supply reliability has consistently attracted extensive research in recent times, although concerns continue to be raised over their adverse impact on the normal grid operation at high penetration levels. These concerns largely stem from the limited controllability of most DPG systems, which tend to exhibit large output impedance variation, and non-deterministic power output characteristics. There has therefore also been a growing need to develop effective control strategies that can enhance the overall impact of the DPG systems on the grid operation, thus improving their synergistic properties, and probably also enabling an even higher penetration level into the utility grid. In line with this identified need, this thesis discusses the modeling and controller design for an inverter-based DPG system with the capability to effectively operate both in grid-connected and autonomous (i.e. independent of the utility grid) operational modes. The dual-mode operation of the DPG is made possible by incorporating into the inverter interface control scheme the means to ensure seamless transition of the DPG between the grid-connected and autonomous modes of operation. The intention is to have a grid-integrated inverter-based DPG system whose operation approximates that of an online Uninterruptible Power Supply (UPS) system, in that it is able to sustain power supply to the local load in the absence of the grid supply, which would be desirable for critical loads, for which the level of power supply reliability guaranteed by the grid often falls short of the requirements. The work developed in this thesis considers three of the aspects associated with grid-integrated DPG systems that are equipped with autonomous-mode operation capability.
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Johal, Harjeet. „Distributed series reactance a new approach to realize grid power flow control /“. Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26713.
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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.Committee Chair: Divan, Deepakraj M.; Committee Member: Begovic, Miroslav M.; Committee Member: Brown, Marilyn; Committee Member: Harley, Ronald G.; Committee Member: Wolf, Wayne H. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Kulka, Arkadiusz. „Sensorless Digital Control of Grid Connected Three Phase Converters for Renewable Sources“. Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5578.
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Power electronic converters have become popular in the field of power transformation for renewable energy. Power electronics converters achieve high efficiency, and the price of their components is falling, thus making them even more beneficial for renewable energy applications. Those systems coupled to the grid need to withstand certain utility-defined circumstances which may occur during operation. Additionally the new net regulations for large generation plants specify that during specified severe grid disturbances the relatively delicate converters should stay connected supporting the system. For PV inverters the forthcoming standards may optionally add the possibility of reactive power compensation where for wind-power those standards are already in use. This thesis focuses on reliable, sensor-less control of the PWM converters coping with varying grid conditions and existing problems. The thesis presents a variety of digital control solutions for interfacing PWM converter with the grid, synchronization, sensorless operation and grid impedance detection. The introductory chapter gives the fundamental theory about three-phase converters and control.The following chapters deal with unbalanced condition and symmetric component decomposition, which is the tool to cope with unbalanced grid voltages or currents. A sensor-less operation method using dual frame virtual flux model is presented with good results. In addition sensor-less synchronization to the grid is shown. Moreover an algorithm based on virtual flux for grid inductance estimation is also successfully demonstrated. Knowing the grid inductance is important during weak grid operation, since it is needed in order to provide unity power factor to the point of common connection. At the end of the thesis, a control algorithm for voltage harmonic compensation during stand alone operation is presented. The presented algorithm gives the possibility to supply high quality power in isolated islands, where the load is unknown. Furthermore, this algorithm can be successfully used for UPS applications. The last chapter applies the voltage harmonic control to the Z-source converter having the possibility of achieving higher ac voltage than in conventional VSI, results are promising.
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Badran, Ahmad. „Integrating Wind Power into The Electric Grid : Predictive Current Control Implementation“. Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-99640.
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The increasing penetration of wind power into the power system dominated by variable-speed wind turbines among the installed wind turbines will require further development of control methods. Power electronic converters are widely used to improve power quality in conjunction with the integration of variable speed wind turbines into the grid. In this thesis, a detailed model of the Predictive Current Control (PCC) method will be descripts for the purpose of control of the grid-connected converter. The injected active and reactive power to the grid will be controlled to track their reference value. The PCC model predicts the future grid current by using a discrete-time model of the system for all possible voltage vectors generated by the inverter. The voltage vector that minimizes the current error at the next sampling time will be selected and the corresponding switching state will be the optimal one. The PCC is implemented in Matlab/Simulink and simulation results are presented.
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Sastry, Jyoti. „Direct AC control of grid assets“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41109.
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The objective of the proposed research is to investigate feasible approaches to dynamic control of the power grid. Growth in the demand for electric power, and an increase in the penetration of renewable energy resources are causing congestion on an already aging power grid. Conventional grid control involves the use of static assets that operate on long time scales. These assets provide no dynamic control on the grid, and are typically used for scheduled support. Existing solutions (FACTS devices) to dynamic grid control have seen minimal market penetration because of high cost and low reliability. The proposed research provides a solution for dynamic control of the power grid that augments existing grid assets with a thin AC converter (TACC) to realize enhanced dynamic control. The TACC is a direct AC converter with filter elements and no bulk energy storage that dynamically reflects the asset value on the grid. The converter has a fail-normal mode of operation that returns the asset to its initial operating state, thereby not degrading system reliability. Some applications of TACCs include Inverter-Less STATCOMs and Controllable Network Transformers, which are realized by augmenting shunt VAR capacitors and load tap changers respectively. The principle of virtual quadrature sources is proposed to enable conditioning of AC voltages and currents. The concept is a novel method to realize control of phase angle and, or harmonics in single-phase AC converters, with no bulk energy storage. This concept is used to control the TACC and provides the asset with significantly enhanced control capabilities. Scaling of the TACC to utility voltage and power levels has been addressed by proposing a novel multilevel direct AC converter. The concept proposes the use of commercially available low cost semiconductor devices to realize high power converters. The specific application chosen to validate the concept of TACCs, through a medium voltage design, is the Inverter-less STATCOM.
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Liu, Kai, und 劉愷. „Optimal dispatch and management for smart power grid“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46336680.
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Kim, Rae-Young. „Improved renewable energy power system using a generalized control structure for two-stage power converters“. Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28932.
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The dissertation presents a generalized control structure for two-stage power converters operated in a renewable energy power system for smart grid and micro grid systems. The generalized control structure is based on the two-loop average-mode-control technique, and created by reconstructing the conventional control structure and feedback configuration. It is broadly used for both dc-dc and dc-ac power conversion based on the two-stage converter architecture, while offering several functionalities required for renewable energy power systems. The generalized control structure improves the performance and reliability of renewable energy power systems with multiple functionalities required for consistent and reliable distributed power sources in the applications of the smart grid and micro grid system.
The dissertation also presents a new modeling approach based on a modification of the subsystem-integration approach. The approach provides continuous-time small-signal models for all of two-stage power converters in a unified way. As a result, a modeling procedure is significantly reduced by treating a two-stage power converter as a single-stage with current sinking or sourcing. The difficulty of linearization caused by time-varying state variables is avoided with the use of the quasi-steady state concept.
The generalized control structure and modeling approach are demonstrated using the two-stage dc-dc and dc-ac power conversion systems. A battery energy storage system with a thermoelectric source and a grid-connected power system with a photovoltaic source are examined. The large-signal averaged model and small-signal model are developed for the two demonstrated examples, respectively. Based on the modeling results, the control loops are designed by using frequency domain analysis. Various simulations and experimental tests are carried out to verify the compensator designs and to evaluate the generalized control structure performance.
From the simulation and experimental results, it is clearly seen that the generalized control structure improves the performance of a battery energy storage system due to the unified control concept. The unified control concept eliminates transient over-voltage or over-current, extra energy losses, power quality issues, and complicated decision processes for multiple-mode control. It is also seen that the generalized control structure improves the performance of a single-phase grid-connected system through increased voltage control loop bandwidth of the active ripple current reduction scheme. As a result of the increased loop bandwidth, the transient overshoot or undershoot of the dc-link voltage are significantly reduced during dynamic load changes.Ph. D.
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Cavraro, Guido. „Modeling, Control and Identification of a Smart Grid“. Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424251.
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We are in front of an epochal change in the power distribution and generation scenario. The increasing request of energy, the energy dependency of several countries from few foreign nations endowed with oilfield or gas field, and, on the other hand, the climate change and environmental issues are the main explanation of the recent development and spread of renewable distributed energy generation technologies. Examples of them
are photovoltaic panels, wind turbines or geothermal, biomass, or hydroelectric. They are called small-size generators, or micro-generator, since the amount of power they can produce is significantly lower than the one produced by the huge, classical power plants. These distributed energy resources (DERs) are located close to where electricity is used, in the distribution network. Furthermore, they are connected to the electrical grid via electronic interfaces, the inverters, that could allow us to control the power injected into the grid. This thesis is focused on the study of some crucial aspects of this new energetic
scenario:
1. Modeling: we recall the classical models and a recent linearized one of the power systems, that will be very useful for the design and the analysis of our algorithms.
2. Optimal Reactive Power Flow (OPRF) problem: in this part we recall classical and recent algorithms that deal with the reactive power regulation. In particular, we focus on the ones that solve the OPRF problem, i.e. the problem of the amount of reactive power to be injected by each micro-generators, in order
to achieve “optimal” performance. We choose, as an optimality achievement, the minimization of the line losses. Finally we derive and propose our OPRF algorithm, providing formal proves of its convergence to the optimal solution.
3. Optimal Power Flow (OPF) problem: the OPF problem’s aim is to find an operating point of the power system that optimize a cost function (tipically the generation cost) satisfying the power demand and some operative constraints. After recalling the most popular algorithms that solve the OPF problem, we propose two
of them. In this framework there are mainly two possible scenarios. The first is related to the “utility point of view”, where the total cost accounts for the production cost of the energy (that comes from big generation plants such as nuclear or hydro-electrical plants) and for the remuneration to be paid to the owners of DERs. In this framework, the utility imposes a behavior procedure to be followed by the producers to compute the amount of energy they have to inject into the grid to minimize the total cost. The first algorithm deal with this scenario. The second one is related to the “producer point of view”. Since the owners of the DERs are paid proportionally to the energy that they inject, they would like to
maximize the power they inject, while keeping satisfied some operative constraints. The result is a game among the agents. A first treatment on this scenario is given by the second algorithm.
4. Switches monitoring for topology identification: in this part, after a literature review, we propose a algorithm for the identification of switches actions. They modify the topology of the electrical grid, whose knowledge is fundamental for monitoring, control and estimation. This algorithm works analyzing how the phasorial voltage profile vary and recognize a kind of signature left by the switches status change.Stiamo vivendo un cambiamento epocale dello scenario di produzione e distribuzione dell’energia. L’incremento della richiesta di energia, il fatto che molte Paesi dipendano energeticamente da poche nazioni ricche di giacimenti di gas o petroliferi e, inoltre, il cambiamento climatico e l’inquinamento costituiscono la ragione principale del recente sviluppo e diffusione di tecnologie per la generazione di energia da fonte rinnovabili. Alcuni esempi ne sono i pannelli fotovoltaici oppure generatori eolici, geotermici, idroelettrico o dalle biomasse. Essi sono generatori di piccole dimensione, o micro-generatori, visto che le loro dimensioni e la quantità di energia che producono sono decisamente inferiori a quelle dei grandi, classici impianti di generazioni. Queste fonti distribuite di energia (DERs) si trovano vicino agli utilizzatori, nella rete di distribuzione. Inoltre, essi sono collegati alla rete attraverso interfacce elettroniche, gli inverter, che ci potrebbero permettere di controllare la quantità di potenza che essi iniettano. Questa tesi si concentra sullo studio di alcuni aspetti cruciali di di questo nuovo scenario energtico, e è composta da quattro parti principali, ciascuna delle quali tratta un aspetto diverso. Esse sono: 1. Modellistica: qui si richiamano i modelli classici e un recente modello linearizzato, che sarà utile per la progettazione e l’analisi degli algoritmi proposti, dei sistemi di potenza. 2. Ottimizzazione dei flussi di potenza reattiva: in questa parte si richiamano i classici e i più recenti algoritmi di gestione della potenza reattiva. In particolare ci si concentra su quelli che ne ottimizzano i flussi, cioè che si focalizzano sul problema di decidere quanta potenza reattiva ciascun micro-generatore deve iniettare se si vogliono ottenere delle prestazioni “ottime”. Come indice di ottimalità è stata scelta la miniizzazione delle perdite sulle linee. Infine viene progettato e analizzato il nostro algoritmo di ottimizzazione, fornendo dimostrazione formale della sua convergenza. 3. Ottimizzazione dei flussi di potenza: lo scopo di questo problema è quello di trovare una configurazione che ottimizza una funzione costo (di solito il costo di generazione) e che soddisfa alcuni vincoli operativi. Dopo aver richiamato i più famosi algoritmi che risolvono questo problema, ne vengono proposti due. Questo perchè vi sono principalmente due scenari. Il primo è connesso al punto di “vista dell’utility”, dove il costo tiene conto sia dell’effettivo costo di generazione dell’energia (che arriva dai grandi impianti di generazione, quali centrali nucleari o idroelettriche) e della remunerazione che deve essere data ai proprietari delle DERs per l’energia che producono. In questo caso , l’utility impone una procedura per calcolare la potenza da iniettare per minimizzare il costo totale. Il primo algoritmo rientra in questo scenario. Il secondo è connesso al punto di “vista del proprietario di DERs”. Poichè questi viene pagato proporzionalmente alla quantità di energia che inietta, vorrebbe massimizzare la potenza che inietta, soddisfando comunque alcuni vincoli operativi. Ne viene fuori un conflitto fra i diversi proprietari. Una trattazione di questo scenario è data dal secondo algoritmo. 4. Controllo degli interruttori per l’identificazione della topologia: in questa parte, dopo una revisione della letteratura, viene proposto un algoritmo per l’identificazione delle azioni degli interruttori nella rete. Queste modificano la topologia della rete elettrica, la cui conoscenza è fondamentale per il controllo, la supervisione e la stima. Questo algoritmo analizza le variazioni dei profili delle tensioni fasoriali e cerca di riconoscere in esse una sorta di firma della particolare azione degli interruttori.
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Spaizman, Daniel. „Grid-Scale Energy Storage: A Proposed Control Algorithm for Sodium Sulfur Batteries“. DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1279.
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With carbon dioxide levels in our atmosphere reaching record highs and 2020 quickly approaching, California is expected to pave the way for the United States in terms of replacing fossil fuel generation facilities with various renewable energy power plants. It is well documented that the inherent variability and limited duty cycle of renewables has hindered their growth. Energy storage technologies represent the bridge that can help us cross the divide from where we stand to where we must stand in the next 6 years. Utility companies value services such as peak shaving, voltage support, and frequency regulation, all of which energy storage technologies can provide. Commercial and residential clients’ of the utility will begin to install their own storage systems once properly incentivized. In this paper, a control algorithm for Sodium Sulfur batteries is proposed with hopes that the aforementioned services will be provided to the utilities while system owners realize profit.
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Tarisciotti, Luca. „Model predictive control for advanced multilevel power converters in smart-grid applications“. Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27742/.
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In the coming decades, electrical energy networks will gradually change from a traditional passive network into an active bidirectional one using concepts such as these associated with the smart grid. Power electronics will play an important role in these changes. The inherent ability to control power flow and respond to highly dynamic network will be vital. Modular power electronics structures which can be reconfigured for a variety of applications promote economies of scale and technical advantages such as redundancy. The control of the energy flow through these converters has been much researched over the last 20 years. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a Cascaded H-Bridge converter, configured to function as a solid state substation. The work considers the derivation and application of Dead Beat and Model Predictive controllers for this application and scrutinises the technical advantages and potential application issues of these methodologies. Moreover an improvement to the standard Model Predictive Control algorithm that include an intrinsic modulation scheme inside the controller and named Modulated Model Predictive Control is introduced. Detailed technical work is supported by Matlab/Simulink model based simulations and validated by experimental work on two converter platforms, considering both ideal and non-ideal electrical network conditions.
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Roslan, Nurul Fazlin. „Control strategy of grid connected power converter based on virtual flux approach“. Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/673388.
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Distributed Generation (DG) provides an alternative to the Centralized Generation (CG) by means of generating electricity near to the end user of power with the employment of small-scale technologies to produce electricity, mainly using Renewable Energy Sources (RES). The prospects of renewable energy integration during the next years are still very optimistic.
This PhD dissertation is made to provide an alternative control framework for the grid connected power converter by adopting the virtual flux concept in the control layer. This dissertation can be divided into three main topics. The 1st topic presents the voltage sensorless control system for the grid-connected power converter. The control system presented is done without depending on AC-voltage measurement where the grid synchronization is based on the Virtual Flux (VF) estimation. In this regard, the Frequency Locked Loop (FLL) is used in conjunction with the estimation scheme to make the system fully adaptive to the frequency changes. This voltage sensorless application is useful for reducing cost and complexity of the control hardware. It is also can be utilized in case of limited reliability or availability of voltage measurements at the intended point of synchronization to the grid. Considering that most previous studies are based on the VF estimation for the case of power converter connected to the grid through the L-filter or LC-filter, this dissertation is focused on the power converter connected to the grid through the LCL filter. The Proportional Resonant (PR) current controller is adopted in the inner loop control of the power electronics-based converter to test the performance of such system.
Another control method based on VF synchronization that permits to control the active and reactive power delivery in a remote point of the grid is also presented in this dissertation. This is due to the fact that the VF is implemented that the voltage in a remote point of the line can be estimated. As it will be shown in simulations and experiments, the proposed control scheme provides a good tracking and dynamic performance under step changes in the reference power. The fast synchronization and the smooth reference tracking achieved in transient conditions have demonstrated the effectiveness of the Dual Second Order Generalized Integrator controlled as Quadrature Signal Generator (DSOGI-QSG) and also the current controller used in the proposed system. In addition to the power control itself, this study could also benefit the frequency and the voltage regulation methods in distributed generation applications as for instance in microgrid.
Considering the fact that the grid connected power converter can be controlled as a virtual synchronous generator where the flux is a variable to be used for controlling its operation, this dissertation also presents a Virtual Synchronous Flux Controller (VSFC) as a new control framework of the grid connected power converter. In this regard, a new control strategy in the inner loop control of the power converter will be proposed. The main components of the outer loop control of VSFC are based on the active and reactive power control. The results presented show that the VSFC works well to control the active and reactive power without considering any synchronization system. The inner loop control is able to work as it is required, and the measurement flux is able to track the reference flux without any significant delays.
All the work presented in this dissertation are supported by mathematical and simulation analysis. In order to endorse the conclusions achieved, a complete experimental validations have been conducted before wrapping this dissertation with a conclusion and recommendation for future enhancement of the control strategies that have been presented.Sistemes d'energia elèctrica
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Omar, Moien. „Power Converters and Control for Grid Connected Microgrids under Unbalanced Operating Conditions“. Doctoral thesis, Università di Catania, 2015. http://hdl.handle.net/10761/3728.
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Nowadays, Renewable Energy Sources (RESs) have become more attractive and affordable due to recent advances in power electronic devices and control systems. Micro-Grids (MGs) represent a new paradigm of electrical grids with Distributed Generation (DG) units: they are generally composed of power converters, RESs, Energy Storage Systems (ESSs), local loads with measurement and control systems.
MGs have the potential to operate in both, grid connected and islanded mode. During islanded mode, ESSs are essential for MGs to enable grid forming control. On the other hand, during grid connected mode, the ESSs allow the MGs to provide different services to the main grid. For example, grid power supporting during peak periods; however, in case of unbalanced operational conditions for MGs, due to single phase loads and single phase generation units, the power exchange between MGs and the main grid will add negative effects to the main grid.
Since the MG is supposed to be grid friendly when connected to the external grid, the unbalanced currents should preferably be handled within the MG. Therefore, the power converters of MGs have to provide the zero sequence and negative sequence currents.
The main objective of this thesis is to obtain grid friendly MGs, in order to improve the functionality of MGs during the grid connected mode, under unbalanced operating conditions.
Power converters with ESSs can be adopted to mitigate the negative effects of unbalanced grid connected MGs. However, suitable control strategies are required. In this thesis, a control strategy based on vector control and symmetrical components is proposed for three-phase four-legs power converter interfaces Energy Storage Batteries (ESBs) to obtain a Multi-Functional Power converter (MFPC), in order to resolve the problems of the unbalanced three phase currents, and to the reactive power compensation.
Several working conditions have been analyzed, and solutions for some common and frequent critical conditions, such as the imbalance of the power system due to single-phase loads and single phase DGs have been presented. Discussions of technical issues like output filter design and four legs VSIs modulation techniques, synchronization, power converters topologies and control have also been discussed.
The proposed control strategy of MFPC is able to mitigate the negative effects of grid connected MGs such as, unbalanced and reactive power compensation. This allows the MGs to become grid friendly , even it is working under highly unbalanced and poor power factor conditions, and also performs power management to optimize the MGs supporting services with smart grid functionality.
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Alves, Montanari Allan. „Enhanced instantaneous power theory for control of grid connected voltage sourced converters under unbalanced conditions“. IEEE Transactions on Power Electronics, 2017. http://hdl.handle.net/1993/32184.
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This thesis introduces a new method especially designed to control the instantaneous power in voltage sourced converters operating under unbalanced conditions, including positive, negative and zero sequence content. A transformation technique, labelled mno transformation, was developed to enable the decomposition of the total instantaneous power flowing on three-phase transmission topologies into constant and oscillating terms. It is applied to three-wire and four-wire schemes, especially accommodating zero sequence unlike previous approaches. Classical and modern electric power theories are presented, particularly focusing on their definitions for adverse AC scenarios. The main mathematical transformations conceived to analyze such situations are summarized, showing their respective advantages and disadvantages. An enhanced instantaneous power theory is introduced. The novel proposed power equations, named mno instantaneous power components, expands the application of the p-q theory, which is attached to the αβ0 transformation. The mno instantaneous power theory is applied to develop an innovative power control method for grid connected voltage sourced converters in order to minimize power oscillations during adverse AC scenarios, particularly with zero sequence content. The method permits to sustain constant instantaneous three-phase power during unbalanced conditions by controlling independently the constant and the oscillating terms related to the instantaneous power. The effectiveness of the proposed control approach and the proposed power conditioning scheme was demonstrated using electromagnetic transient simulation of a VSC connected to an AC system.May 2017
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Geury, Thomas. „Smart matrix converter-based grid-connected photovoltaic system for mitigating current and voltage-related power quality issues on the low-voltage grid“. Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/243967.
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The increasing penetration of distributed energy resources, in particular Photovoltaic (PV) production units, and the ever-growing use of power electronics-based equipment has led to specific concern about Power Quality (PQ) in the Low-Voltage (LV) grid. These include high- and low-order current harmonics as well as voltage distortion at the point of common coupling. Solutions to overcome these issues, meeting international grid codes, are being proposed in the context of smart energy management schemes.This work proposes a novel three-phase topology for a PV system with enhanced PQ mitigation functionality, tackling the corresponding control challenges.First, a single-stage current-source inverter PV system with active filtering capability is preferred to the more common two-stage voltage-source inverter topology with additional voltage-step-up converter. The system also guarantees a nearly unitary displacement power factor in the connection to the grid and allows for Maximum Power Point Tracking (MPPT) with direct control of the PV array power. The grid-synchronised dq-axis grid current references are generated for the mitigation of nonlinear load low-order current harmonics, without the need for additional measurements. Active damping is used to minimise grid-side filter losses and reduce high-order harmonics resulting from the converter switching.Results on a 500W laboratory prototype confirm that active damping reduces the switching harmonics in the grid currents and active filtering properly mitigates the low-order current harmonics. The MPPT algorithm works effectively for various irradiance variations. Second, a PV system with a novel Indirect Matrix Converter (IMC)-based unified power quality conditioner topology is developed for enhanced current and voltage compensation capability, with compactness and reliability advantages. PQ issues such as current harmonics, and voltage sags, swells, undervoltage and overvoltage are mitigated by the shunt and series converters, respectively.The more common Space Vector Modulation (SVM) method used in IMCs is developed for this specific topology. In particular, a new shunt converter modulation method is proposed to additionally control the PV array current with zero switching vectors, resulting in a specific switching sequence.A direct sliding mode control method is also studied separately for the shunt and series converters, so that the zero-vector modulation method of the shunt converter can be used, with no sensitive synchronisation of the switching signals; this contrasts with the SVM method. A new dc link voltage modulation method with 12 voltage zones, instead of 6, is proposed to help overcome the limitation in the choice of shunt converter switching vectors due to the positive dc link voltage constraint.Results are obtained for the direct method on a 1 kW laboratory prototype with optimised IMC dc link connection and alternative shunt converter switching transitions to guarantee a positive dc link voltage. Current and voltage compensation capabilities are confirmed by tests in various operating conditions.Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished
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Gao, Siyu. „Grid synchronisation of VSC-HVDC system“. Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/grid-synchronisation-of-vschvdc-system(6de14261-b0cd-4a82-bfb9-2ccaae012c4e).html.
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This thesis investigates issues affecting grid synchronisation of VSC-HVDC systems with particular regard to, but not limited to, offshore wind power generation during the complex but potentially serious behaviours following solar storms. An averaged value model (AVM) for the contemporary modular multilevel converter (MMC) based VSC-HVDC system is developed and is used in combination with different phase-locked loop (PLL) models and the unified magnetic equivalent circuit (UMEC) transformer model to assess the impacts of geomagnetically induced current (GIC) on grid synchronisation of an offshore VSC-HVDC system. GIC is DC current flowing in the earth caused by strong geomagnetic disturbance events. GIC enters the electric utility grid via the grounded transformer neutral and can cause severe saturation to transformers. This in turn causes disruptions to grid synchronisation. The main contribution of this thesis is that effects of GIC are studied using the UMEC transformer model, which can model saturation. The assessment leads to the development of enhanced fundamental positive sequence control (EFPSC) which is capable of reducing the stress on the system during GIC events. The methods developed can also be applied to other non-symmetrical AC events occurring in VSC-HVDC such as single-phase faults. Additional contributions of the thesis are:A mathematical model of the MMC is derived and forms the foundation of the AVM. The AVM is verified against a detailed equivalent-circuit-based model and shows good accuracy. The PLL is the essential component for grid synchronisation of VSC-HVDC system. Different PLLs are studied in detail. Their performance is compared both qualitatively and quantitatively. This appears to have been done for the first time systematically in the public literature. The UMEC model is verified using hand calculation. Its saturation characteristic is matched to a predefined B-H curve and is also verified. The verifications show that this model is capable of modelling transformer saturation and thus is suitable for this study. The consolidation of the AVM, PLL, UMEC, GIC and EFPSC provides an insight into the how the MMC based VSC-HVDC system behaves under severe geomagnetic disturbances and the possible methods to mitigate the risks and impacts to the power grid.
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Ekström, Ellen. „Using Shared Priorities to Support Training of Nuclear Power Plant Control Room Crews“. Thesis, Linköpings universitet, Institutionen för datavetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-120076.
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Swedish nuclear power plant control room crews have training sessions in full scope simulators every year. These sessions are designed to prepare operators to cope with incidents and accidents. The aim is to develop operators’ knowledge, skills and abilities necessary to operate the nuclear power plant in a safe manner. Training sessions is an opportunity to practice and develop the crews’ teamwork, decision processes and working strategies. The purpose of this study was to explore if and how the instrument Shared Priorities can support training of nuclear power plant control room crews. Shared Priorities is an instrument to measure teams’ shared awareness of a situation and has in earlier studies been used in military and student teams. During the simulator re-training period of control room crews, 14 crews used the instrument Shared Priorities in one or two of their training scenarios. The instrument consists of two steps. Firstly, crew members generate and prioritise a list of five items they think are most important for the crew to cope with in the scenarios current situation. They also rank another crew member’s list. Secondly, the crews and instructors perform a focus group discussion based on the generated lists. Results from questionnaires, focus group discussions and an interview with instructors showed that operators and instructors believe that Shared Priorities can support their training in several ways. Crews see meetings and other disseminations of information as an essential part of maintaining shared understanding of different situations. They believe the instrument may help crews reflect upon and develop their meeting procedures. Operators and instructors also believe that by using the instrument it can help crews to increase their understanding of having a shared situation understanding and shared vision. However the procedure when using Shared Priorities has to be modified in order to be able to support crews’ training in an optimal way.
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Turner, Robert Walter. „Improving the performance of digitally-controlled high power grid-connected inverters“. Thesis, University of Canterbury. Electrical and Computer Engineering, 2013. http://hdl.handle.net/10092/7614.
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The availability of high speed and high power switching devices, such as the IGBT, has opened the opportunity for an increasing number of grid-connected inverter applications that have historically been unachievable. Recently, the number of inverter applications has surged, with now the focus being on increasing the relative performance and power capability. Such applications include UPSs, dynamic voltage restorers, STATCOMs, frequency converters and distributed grid sources such as solar panels.
The inverter switching frequency limits its associated bandwidth and hence performance. Every application can benefit by reduction of the extent of this limitation. While state of the art devices like IGBTs enable such applications, the onus is now on developing high bandwidth digital controllers; the ability to connect multiple devices together to achieve power scaling; and having the confidence that the applications will work with other systems on a grid.% Solutions for for improving the inverter performance, ability to scale the power and operation compliance with other grid-connected devices are sought.
Constraints and limitations imposed by the hardware and traditional continuous-time derived controllers are identified. A discrete-time direct design controller is then developed specifically for digital controllers, that for the same inverter configuration, achieves twice the bandwidth of a well-tuned traditional controller. An important feature of a controller is having the configurability of being able to choose inverter bandwidth over stability margin.
To provide power scaling above that of a single switching module, investigations are performed on the suitability of actively paralleling inverter modules. Both the use of the developed discrete direct design controller and the identification of potential inter-module instabilities for a particular configuration enables the application of paralleled inverters. The operation is confirmed through the application of a sixteen paralleled module inverter system.
Finally, a graphical analysis technique is introduced for analysing complex grids that may include inverter systems. The graphical technique demonstrates stability constraints with a range of sources and loads, including both inverters and rotating machines, which historical analysis techniques have been unable to do.
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Siniscalchi, Minna Sara. „Advanced wind farm control strategies for enhancing grid support“. Doctoral thesis, TDX (Tesis Doctorals en Xarxa), 2019. http://hdl.handle.net/10803/669244.
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Nowadays, there is rising concern among Transmission System Operators about the declining of system inertia due to the increasing penetration of wind energy, and other renewable energy systems, and the retirements of conventional power plants. On the other hand, by properly operating wind farms, wind generation may be capable of enhancing grid stability and ensuring continued security of power supply. In this doctoral thesis, new control approaches for designing wind farm optimization-based control strategies are proposed to improve the participation of wind farms in grid support, specially in primary frequency support.Hoy en día, existe una significativa preocupación entre los Operadores de Sistemas de Transmisión sobre la cresciente penetración de le energía eólica y la tendiente eliminación de las centrales eléctricas convencionales que implica la disminución de la inercia del sistema eléctrico. Operando adecuadamente los parques eólicos, la generación eólica puede mejorar la estabilidad de la red eléctrica y garantizar la seguridad y un continuo suministro de energía. Esta tesis doctoral propone nuevas estrategias para diseñar controladores basados en optimización dinámica para parques eólicos y mejorar la participación de los parques eólicos en el soporte de la red eléctrica. En primer lugar, esta tesis doctoral presenta los enfoques clásicos para el control de parques y turbinas eólicas y cómo los conceptos de control existentes pueden ser explotados para hacer frente a los nuevos desafíos que se esperan de los parques eólicos. Esta tesis doctoral asigna un interés especial a cómo formular la función objetivo de que la reserva de potencia sea maximizada, para ayudar por el suporte de frequencia, y al mismo tiempo seguir la potencia demandada por la red. Sin embargo, el impacto de la estela de viento generada por una turbina sobre otras turbinas necesita ser minimizado para mejorar la reserva de potencia. Por lo tanto, a lo largo de esta tesis se proponen estrategias de control centralizado para parques eólicos enfocadas en distribuir óptimamente la energía entre las turbinas para que el impacto negativo de la estela en la reserva de potencia total se reduzca. Se discuten dos técnicas de control para proporcionar los objetivos de control mencionados anteriormente. Un algoritmo de control óptimo para encontrar la mejor distribución de potencia entre las turbinas en el parque mientras se resuelve un problema iterativo de programación lineal. En segundo lugar, se utiliza la técnica de control predictivo basada en modelo para resolver un problema de control multi-objetivo que también podría incluir, junto con la maximización de reserva de potencia, otros objetivos de control, tales como la minimización de las perdidas eléctricas en los cables de la red de interconexión entre turbinas y un controlador/supervisor. Además, la investigación realizada resalta la capacidad de las estrategias de control propuestas en esta tesis para proporcionar mayor reserva de potencia respecto a los conceptos comúnmente usados para distribuir la potencia total del parque eólico. La idea principal detrás del diseño de una estrategia de control de parques eólico es de encontrar una solución óptima dentro de un cálculo computacional relativamente bajo. Aunque los controladores centralizados propuestos en esta tesis reaccionan rápidamente a los cambios en la potencia de referencia enviada desde el controlador, algunos problemas pueden ocurrir cuando se consideran parques eólicos de gran escala debido a los retrasos existentes por el viento entre turbinas. Bajo estas circunstancias, la producción de energía de cada turbina está altamente acoplada con la propagación de la estela y, por ende, con las condiciones de funcionamiento de las otras turbinas. Esta tesis doctoral propone un esquema de control de parques eólicos no centralizados basado en una estrategia de partición para dividir el parque eólico en sub-conjuntos independientes de turbinas. Con la estrategia de control propuesta, el tiempo de cálculo se reduce adecuadamente en comparación con la estrategia de control centralizado mientras que el rendimiento en la distribución óptima de potencia es ligeramente afectado. El rendimiento de todas las estrategias de control propuestas en esta tesis se prueba con un simulador de parque eólico que modela el comportamiento dinámico del efecto de estela mediante el uso de un conocido y consolidado modelo dinámico de estela y, para un análisis más realista, algunas simulaciones se realizan con software avanzado basado en la técnica de Large Eddy Simulation.
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Masood, Tariq. „Improvement of voltage and power flow control in the GCC power grid by using coordinated FACTS devices“. Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589638.
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This work presents HVDC/FACTS control device implementation framework in the Gulf cooperative council’s countries. It comprises of five layers of FACTS control devices (STATCOM, SSSC, UPFC, HVDC and centralized/De-centralized Control). This five-layer architecture is designed in order to configure and produce the desired results; based on these outcomes, GCC power system network control and operational problems can be identified and addressed within the control architecture on the GCC power grid. In the context of power FACTS-FRAME, this work is to identify and determine a number of power systems operational and control problems which are persistent on the GCC power grid e.g. poor voltage quality (SAG-Swell), poor load flow control, and limited power transfer capacity issues. The FACTS-FRAME is configured and synthesized by integrating multiple FACTS control devices (STATCOM, SSSC, UPFC) in parallel at different locations on the GCC power grid in order to meet stringent power system control and operational requirements with improved power transfer capacity, controllability and reliability. The mathematical models are derived to indentify and determine operational constraints on the GCC power grid by incorporating real-time and estimated data and the acquired desired results. Herein, FACTS-FRAME is designed to handle distributed computation for intensive power system calculation by integrating multiple FACTS devices on multiple networks within the GCC power network. Distributed power flow algorithms are also derived in order to understand and implement centralized and decentralized control topologies as appropriate. The simulation results indicate the feasibility of FACTS devices implementation and their potential benefits under current operating conditions on the GCC power grid.
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Raza, Muhammad. „Offshore grid control of voltage source converters for integrating offshore wind power plants“. Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461835.
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The offshore grid in North and Baltic Sea can help Europe to achieve 2020 and 2030 renewable energy target to counter climate changes . The formation of offshore grid requires the interconnection between several offshore wind power plants with multiple onshore grids. A voltage source converter based high voltage direct current transmission system is suitable to operate such an integrated offshore network. The offshore grid will enhance the trade between countries, provide better infrastructure for offshore wind power plants integration, and improve the energy market.
This thesis presents the control system design of voltage source converter to operate an offshore grid. The offshore grid is built gradually , starting from the integration of a single offshore wind power plan! till combined offshore AC and OC network in arder to perform the power system analysis associated with the networks such as steady-state power flow, dynamic behavior, network stability, and short circuit response. The research presents the method of determining control parameters with respect of power distribution and network stability requirements.
The research presents the frequency and voltage droop schemes to enhance the grid-forming mode of voltage source converter to operate in parallel in the offshore grid. A multi-objectives optimal power flow algorithm is proposed to determine the frequency and voltage droop gains in order to control the active and reactive power distribution among converters. Later, the impact of these droop gains on network dynamics and stability are analyzed. The study shows that the converter performance influences the offshore AC network stability in conjunction with the droops control loop.
Furthermore, a short circuit and frequency coordinated control schemes are presented for both offshore wind generation units and grid-forming converters . The frequency coordinated control scheme reduces !he wind power up to the maximum available export capacity after the disturbance in the offshore grid. lt is suggested that !he coordination control mus! have both frequency and over voltage control for improved transient response.
In the end, converter control of mullí-terminal OC network and its integration with the offshore AC network has been presentad. The research demonstrate the converter ability to control the distribution of power among the transmission system while ensuring the network stability. The finding of the research can be applied to derive the information and recommendation for the future wind power plants projects.Las redes eléctricas marítimas en el Norte y en el Mar Báltico pueden ayudar a Europa a conseguir los objetivos para 2020 y 2030 de combatir el cambio climático. La formación de la red eléctrica marítima requiere la interconexión entre varios parques eólicos marinos con múltiples redes eléctricas en tierra. Un convertidor de la fuente de voltaje basado en el sistema de transmisión de corriente directa de alto voltaje es el apropiado para poder operar una red marítima integrada. Las redes eléctricas marítimas aumentarán el comercio entre países, proveerán una mejor infraestructura para la integración de los parques eólicos marinos y mejorarán el mercado energético. Esta tesis presenta el diseño del sistema de control del convertidor de las fuentes de voltaje para operar una red eléctrica marítima. La red eléctrica marítima se construye gradualmente, empezando por la integración de un solo parque eólico marino hasta la combinación de redes eléctricas marítima en CA y CD, esto para mejorar el análisis del sistema de potencia asociado con las redes, tales como el flujo de potencia en estado estacionario, el comportamiento dinámico, la estabilidad de la red y la respuesta en corto circuito. La investigación presenta el método de determinación de parámetros de control con respecto a la distribución de potencia y los requerimientos de estabilidad de la red. La investigación presenta los esquemas de frecuencia y la caída de voltaje para mejorar el método de formación de red del convertidor de la fuente de voltaje y operar en paralelo con la red eléctrica marítima. Se propone un algoritmo de múltiples objetivos para lograr un flujo de potencia óptimo, determinar las ganancias en la frecuencia y en la caída de voltaje y así lograr controlar la distribución de potencia activa y reactiva entre los convertidores. Después, se analiza el impacto de estas ganancias en la dinámica y estabilidad de la red. El estudio nos muestra que el desempeño del convertidor influencia la estabilidad de la red eléctrica marítima en CA en conjunto con el lazo de control de la caída. Así mismo, se presentan los esquemas de control coordinado de frecuencia y corto circuito, aplicados para las unidades de generación eólica marítima y los convertidores en red. El esquema de control coordinado de frecuencia reduce la potencia eólica hasta la máxima capacidad de exportación disponible después de las perturbaciones en la red eléctrica marítima. Se sugiere que la coordinación del control debe de tener control sobre la frecuencia y el sobre voltaje para mejorar la respuesta en transitorios. Por último, se presenta el control del convertidor de las multiterminales en la red CD y su integración con la red eléctrica marítima en CA. La investigación demuestra la habilidad que posee el convertidor para controlar la distribución de potencia, junto con el sistema de transmisión, mientras se asegura la estabilidad de la red. Los hallazgos de esta investigación pueden ser aplicados para obtener información y recomendaciones en los futuros proyectos de parques eólicos.
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Luu, Hong Viet. „Grid friendly digital control of active front-end converters minimizing of power interferences“. Dresden TUD-Press, 2006. http://deposit.ddb.de/cgi-bin/dokserv?id=2825500&prov=M&dok_var=1&dok_ext=htm.
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Fulhu, Miraz Mohamed. „Active human intelligence for smart grid (AHISG) : feedback control of remote power systems“. Thesis, University of Canterbury. Mechanical Engineering, 2014. http://hdl.handle.net/10092/9582.
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Fuel supply issues are a major concern in remote island communities and this is an engineering field that needs to be analyzed in detail for transition to sustainable energy systems. Power generation in remote communities such as the islands of the Maldives relies on power generation systems primarily dependent on diesel generators. As a consequence, power generation is easily disrupted by factors such as the delay in transportation of diesel or rises in fuel price, which limits shipment quantity. People living in remote communities experience power outages often, but find them just as disruptive as people who are connected to national power grids. The use of renewable energy sources could help to improve this situation, however, such systems require huge initial investments. Remote power systems often operate with the help of financial support from profit-making private agencies and government funding. Therefore, investing in such hybrid systems is uncommon.
Current electrical power generation systems operating in remote communities adopt an open loop control system, where the power supplier generates power according to customer demand. In the event of generation constraints, the supplier has no choice but to limit the power supplied and this often results in power cuts. Most smart grids that are being established in developed grids adopt a closed loop feedback control system. The smart grids integrated with demand side management tools enable the power supplier to keep customers informed about their daily energy consumption. Electric utility companies use different demand response techniques to achieve peak energy demand reduction by eliciting behavior change. Their feedback information is commonly based on factors such as cost of energy, environmental concerns (carbon dioxide intensity) and the risk of black-outs due to peak loads. However, there is no information available on the significant link between the constraints in resources and the feedback to the customers. In resource-constrained power grids such as those in remote areas, there is a critical relationship between customer demand and the availability of power generation resources.
This thesis develops a feedback control strategy that can be adopted by the electrical power suppliers to manage a resource-constrained remote electric power grid such that the most essential load requirements of the customers are always met. The control design introduces a new concept of demand response called participatory demand response (PDR). PDR technique involves cooperative behavior of the entire community to achieve quality of life objectives. It proposes the idea that if customers understand the level of constraint faced by the supplier, they will voluntarily participate in managing their loads, rather than just responding to a rise in the cost of energy. Implementation of the PDR design in a mini-grid consists of four main steps. First, the end-use loads have to be characterized using energy audits, and then they have to be classified further into three different levels of essentiality. Second, the utility records have to be obtained and the hourly variation factors for the appliances have to be calculated. Third, the reference demand curves have to be generated. Finally, the operator control system has to be designed and applied to train the utility operators.
A PDR case study was conducted in the Maldives, on the island of Fenfushi. The results show that a significant reduction in energy use was achieved by implementing the PDR design on the island. The overall results from five different constraint scenarios practiced on the island showed that during medium constrained situations, load reductions varied between 4.5kW (5.8%) and 7.7kW (11.3%). A reduction of as much as 10.7kW (15%) was achieved from the community during a severely constrained situation.
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Zhou, Huafeng, und 周華鋒. „Design of grid service-based power system control centers for future electricity systems“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687429.
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Omole, Adedamola. „Voltage Stability Impact of Grid-Tied Photovoltaic Systems Utilizing Dynamic Reactive Power Control“. Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3615.
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Photovoltaic (PV) DGs can be optimized to provide reactive power support to the grid,
although this feature is currently rarely utilized as most DG systems are designed to
operate with unity power factor and supply real power only to the grid. In this work, the
voltage stability of a power system embedded with PV DG is examined in the context of
the high reactive power requirement after a voltage sag or fault. A real-time dynamic
multi-function power controller that enables renewable source PV DGs to provide the
reactive power support necessary to maintain the voltage stability of the microgrid, and
consequently, the wider power system is proposed.
The loadability limit necessary to maintain the voltage stability of an interconnected
microgrid is determined by using bifurcation analysis to test for the singularity of the
network Jacobian and load differential equations with and without the contribution of
the DG. The maximum and minimum real and reactive power support permissible from
the DG is obtained from the loadability limit and used as the limiting factors in
controlling the real and reactive power contribution from the PV source. The designed
controller regulates the voltage output based on instantaneous power theory at the
point-of-common coupling (PCC) while the reactive power supply is controlled by means
of the power factor and reactive current droop method. The control method is
implemented in a modified IEEE 13-bus test feeder system using PSCAD® power system
analysis software and is applied to the model of a Tampa Electric® PV installation at
Lowry Park Zoo in Tampa, FL.
This dissertation accomplishes the systematic analysis of the voltage impact of a PV DGembedded
power distribution system. The method employed in this work bases the
contribution of the PV resource on the voltage stability margins of the microgrid rather
than the commonly used loss-of-load probability (LOLP) and effective load-carrying
capability (ELCC) measures. The results of the proposed method show good
improvement in the before-, during-, and post-start voltage levels at the motor
terminals. The voltage stability margin approach provides the utility a more useful
measure in sizing and locating PV resources to support the overall power system
stability in an emerging smart grid.
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Chang, Chien-tsung, und 張建聰. „Switchyard Control Room Power Scada System“. Thesis, 2009. http://ndltd.ncl.edu.tw/handle/95981105331854524277.
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碩士逢甲大學
資訊電機工程碩士在職專班
97
「Switchyard Control Room Power Scada System」is a system that is devoted to the remote power monitoring and the dispatch at the switchyard in the power plant. The switchyard is built primarily to connect the power that is produced by generation system and provider system in the power plant. Now, the switchyard is disposed four shifts personnel in shifts, and all of the controls （e.g. state monitor and value record）are operated by personnel at the switchyard. Presently, there are ten generator sets built in power plant. Each generator set has its control room. It is beneficial for the power plant to replace the existing switchyard by an unmanned style with the capability of remote control to save the cost of manpower. This thesis is dedicated to a「Switchyard Control Room Power Scada System」, including complete switch equipment and control, monitor and data acquisition about ten generator sets. The control, monitor and data acquisition of equipments of switchyard can be executed in personal computer. It can achieve the function of remote control by Ethernet and industry standard communication interface to connect remote terminal units, control room of generator sets and plant information system.
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Kumar, Rajeev. „Room Temperature Control using On-Off Controller“. Thesis, 2016. http://ethesis.nitrkl.ac.in/8014/1/2016_BT_RajeevKumar_112EE0238.pdf.
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The objective of the project is to maintain the temperature of a room constant using on-off controller. In this project, a control logic is developed and implemented using electronics components. The room is made of aluminium sheet. The logic circuit drives the bulb and exhauster fan fitted in the room. The bulb is used to heat the room, and the exhaust fan is used to cool the same. The temperature of the room is measured with TMP 103 sensor. The room temperature from the sensor is compared with a set value given from a potentiometer. Depending on the compared value the logic circuit decides its control action to be taken, and the overall system becomes a feedback control system. If the set point value is above the sensor measured value, the bulb is turned on and at the same time fan is turned off to increase temperature. If the temperature measured is above the set point then bulb is turned off and fan is turned on decrease the temperature.
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Chen, Yuan-He, und 陳源和. „Grid-Connected Power Factor Control Strategy for Direct Grid-Connected Excited Synchronous Wind Power Generators with Servo Motor Control“. Thesis, 2019. http://ndltd.ncl.edu.tw/handle/s37h3e.
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碩士國立中山大學
電機工程學系研究所
107
This thesis proposes the direct grid-connected excited synchronous wind power system with servo motor control. The main structure of this system is using coupling to connect excited synchronous generator and servo motor in a coaxial framework. We can precisely control the generator output with the servo motor. Since the excited synchronous generator can operate in high voltage, the usage of power converter is no longer needed. Therefore, we can improve reliability, reach higher quality and achieve efficient grid connection. The servo motor can adjust the frequency and phase of generator output in time to reach the requirement of grid connection. During the grid connection, the motor can improve the power factor so that the output can be applied more efficiently. The servo motor can remain very low power consumption in the process to optimize the application of the wind power. This thesis also proposes a strategy to control the power factor of the system. The strategy controls the generator current phase to lag the main voltage phase and result in a fixed phase difference between the two in order to control the value of the power factor and discuss the influence on generator current in different power factors. It also proposes that the servo motor providing different energy to the system, which can effectively improve the output power of the generator.
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Fong-JhihGuo und 郭鳳枝. „Bidirectional Control of Power Flow between DC Micro-grid and AC Grid“. Thesis, 2016. http://ndltd.ncl.edu.tw/handle/38065587431547124747.
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碩士國立成功大學
電機工程學系
104
In recent years, micro-grid system is one of the key developing roadmap of electric power industry. To solve the unstable supply problem from renewable energy, the DC micro-grid used to be supplemented by several backup resources, like fuel cell and battery. If the DC micro-grid is interconnected with AC grid, the AC side can serve as another backup option. This thesis is to study the control of power flow between DC micro-grid and AC grid using a bidirectional power converter. As renewable energy shortage takes place at DC side, the deficit energy can be supplied from AC grid. On the other hand, as decreased DC loading or excessive renewable energy takes place at the DC side, the redundant energy can be transferred to AC grid. This thesis first describes a three-phase bridge topology controlled by Sinusoidal Pulse-width Modulation. Following that, a synchronous reference frame phase-lock loop method for AC grid connection is illustrated. The proposed three-phase power converter is operated between inverter mode and rectifier mode. As voltage of DC bus is higher than the preset threshold, the power converter effectively operates at inverter mode to transfer excess energy from DC grid to AC grid, and vice versa as the power converter is operating at rectifier mode. The experiment shows that power balance between DC micro-grid and AC grid is achieved by controlling bi-directional power flow.
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Das, Anasuya. „The H∞ Control Method of Grid-Tied Photovoltaic Generation“. Thesis, 2016. http://ethesis.nitrkl.ac.in/9127/1/2016_MT_ADas.pdf.
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Renewable energy is the alternative sources of electrical energy to fulfill energy shortage. micro grid allows to connect multiple renewable energy sources to it. Photovoltaic (PV) generation is one of the major renewable energy sources. PV generation systems directly connected to micro grid brings some problems like voltage deviation, current fluctuation etc. which brings instability into the system. Thus, a smooth micro grid connection with PV system is required. Here H∞ control method based on model matching technique has been adopted for our system. To extract maximum power from PV array, P and O MPPT algorithm has been adopted.
Mathematical modellings for the design of H∞ Controller has been done here.Using Robust control tool box gain of the controller are found, all the eigen values of H∞ control system have negative real part, Hence voltage tracking control system is stable.
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Chen, Jyun-Jia, und 陳俊嘉. „Grid-connected Control Strategy for Direct Grid-connected Excited Synchronous Wind Power Generators with Servo Motor Control“. Thesis, 2018. http://ndltd.ncl.edu.tw/handle/85ejcg.
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碩士國立中山大學
電機工程學系研究所
106
This thesis proposes the direct grid-connected excited synchronous wind power system. The main structure of this system is using coupling to connect excited synchronous generator and servo motor in a coaxial framework. Since we can precisely control the generator output with the servo motor, we can achieve high quality and efficient grid connection. The servo motor can adjust the frequency and phase of generator output in time to reach the requirement of grid connection. Besides, the motor can improve the power factor during the grid connection so that the output can be applied more efficiently. However, the servo motor is able to use as little energy as possible throughout the process to optimize the application of the wind power. Furthermore, with the characteristic that the excited synchronous generator can output directly with high voltage, we can not only reduce the electronic converter but also improve the efficiency and reliability. This thesis also proposes the analysis of system parameter optimization. With multiple data, we compare the effect of the parameters change in each loop on the system and the grid connection. The control loop includes the Maximum Power Tracking, the Frequency Locking, the Phase Locking and the Power Factor Correction, etc.. By observing the motor power, the phase difference between the absolute angle of the transmission shaft and the mains power and the phase difference between the generator output and the mains power, etc., the changes caused by the different parameters are analyzed. As a result, we are able to conclude a set of better result which can be used to deliver the wind energy more efficiently to the grid.