The power converter is one of the key components in power system applications such as high voltage direct current (HVDC) systems and the grid connection of intermittent sources such as wind and solar power. However, the increased penetration of converter-based generation introduces challenges, such as sub-synchronous interaction between the converter control system and the grid. These control interactions are characterized by fast-growing, subsynchronous oscillations (SSO). This thesis deals with the analysis of sub-synchronous control interactions (SSCI) between doubly-fed induction generator (DFIG)-based wind farms and series compensated transmission lines. Moreover, the thesis aims to identify a method for mitigating the sub-synchronous oscillations using a static synchronous compensator (STATCOM), with a supplementary damping controller. The study is based on work in PSCAD/EMTDC and uses a system based on the IEEE first benchmark model, acting as a grid, and the scaled power output of a DFIG turbine model, modeling a wind farm. Initial impedance-based analysis in the frequency domain shows that the DFIG wind farm has a negative resistance throughout the sub-synchronous frequency range. A negative resistance may result in negative damping of the system and further introduce the risk of instability. The wind farm resistance and, in turn, system stability is affected by the current control loop of the DFIG-converter. The transmission line compensation factor largely impacts the system stability, while the power output has a minor effect. A time-domain analysis is performed to verify the result of the frequency domain analysis. Further on, a grid-forming STATCOM is added to the system for VAr compensation. Additional stability analysis shows that even though improvingthe stability, the STATCOM alone is not adequate to mitigate the SSCI. The proposed damping strategy is based on modifying the STATCOM voltage reference andcan be divided into three steps: detecting the SSO, estimating the sub-synchronous component, and modifying the extracted signal. The detection algorithm is based on a half-cycle comparator, while the modification is done through a proportional gain. When estimating the sub-synchronous components, two methods are proposed and compared. The first estimation method is based on a conventional power system stabilizer (PSS) method, and the second is afilter-less method.

<p>In this research, a Split-Shaft Wind Energy Conversion System (SS-WECS) is investigated</p> <p>to improve the performance and cost of the system and reduce the wind power</p> <p>uncertainty influences on the power grid. This system utilizes a lightweight Hydraulic Transmission</p> <p>System (HTS) instead of the traditional gearbox and uses a Doubly-Fed Induction</p> <p>Generator (DFIG) instead of a synchronous generator. This type of wind turbine provides</p> <p>several benefits, including decoupling the shaft speed controls at the turbine and the generator.</p> <p>Hence, maintaining the generator’s frequency and seeking maximum power point</p> <p>can be accomplished independently. The frequency control relies on the mechanical torque</p> <p>adjustment on the hydraulic motor that is coupled with the generator. This research provides</p> <p>modeling of an SS-WECS to show its dependence on mechanical torque and a control</p> <p>technique to realize the mechanical torque adjustments utilizing a Doubly-Fed Induction</p> <p>Generator (DFIG). To this end, a vector control technique is employed, and the generator</p> <p>electrical torque is controlled to adjust the frequency while the wind turbine dynamics</p> <p>influence the system operation. The results demonstrate that the generator’s frequency is</p> <p>maintained under any wind speed experienced at the turbine.</p> <p>Next, to reduce the size of power converters required for controlling DFIG, this research</p> <p>introduces a control technique that allows achieving MPPT in a narrow window of generator</p> <p>speed in an SS-WECS. Consequently, the size of the power converters is reduced</p> <p>significantly. The proposed configuration is investigated by analytical calculations and simulations</p> <p>to demonstrate the reduced size of the converter and dynamic performance of the</p> <p>power generation. Furthermore, a new configuration is proposed to eliminate the Grid-</p> <p>Side Converter (GSC). This configuration employs only a reduced-size Rotor-Side Converter</p> <p>(RSC) in tandem with a supercapacitor. This is accomplished by employing the hydraulic</p> <p>transmission system (HTS) as a continuously variable and shaft decoupling transmission</p> <p>unit. In this configuration, the speed of the DFIG is controlled by the RSC to regulate the</p> <p>supercapacitor voltage without GSC. The proposed system is investigated and simulated in</p> <p>MATLAB Simulink at various wind speeds to validate the results.</p> <p>Next, to reduce the wind power uncertainty, this research introduces an SS-WECS where the system’s inertia is adjusted to store the energy. Accordingly, a flywheel is mechanically</p> <p>coupled with the rotor of the DFIG. Employing the HTS in such a configuration allows the</p> <p>turbine controller to track the point of maximum power (MPPT) while the generator controller</p> <p>can adjust the generator speed. As a result, the flywheel, which is directly connected</p> <p>to the shaft of the generator, can be charged and discharged by controlling the generator</p> <p>speed. In this process, the flywheel energy can be used to modify the electric power generation</p> <p>of the generator on-demand. This improves the quality of injected power to the</p> <p>grid. Furthermore, the structure of the flywheel energy storage is simplified by removing</p> <p>its dedicated motor/generator and the power electronics driver. Two separate supervisory</p> <p>controllers are developed using fuzzy logic regulators to generate a real-time output power</p> <p>reference. Furthermore, small-signal models are developed to analyze and improve the MPPT</p> <p>controller. Extensive simulation results demonstrate the feasibility of such a system and its</p> <p>improved quality of power generation.</p> <p>Next, an integrated Hybrid Energy Storage System (HESS) is developed to support the</p> <p>new DFIG excitation system in the SS-WECS. The goal is to improve the power quality</p> <p>while significantly reducing the generator excitation power rating and component counts.</p> <p>Therefore, the rotor excitation circuit is modified to add the storage to its DC link directly.</p> <p>In this configuration, the output power fluctuation is attenuated solely by utilizing the RSC,</p> <p>making it self-sufficient from the grid connection. The storage characteristics are identified</p> <p>based on several system design parameters, including the system inertia, inverter capacity,</p> <p>and energy storage capacity. The obtained power generation characteristics suggest an energy</p> <p>storage system as a mix of fast-acting types and a high energy capacity with moderate</p> <p>acting time. Then, a feedback controller is designed to maintain the charge in the storage</p> <p>within the required limits. Additionally, an adaptive model-predictive controller is developed</p> <p>to reduce power generation fluctuations. The proposed system is investigated and simulated</p> <p>in MATLAB Simulink at various wind speeds to validate the results and demonstrate the</p> <p>system’s dynamic performance. It is shown that the system’s inertia is critical to damping</p> <p>the high-frequency oscillations of the wind power fluctuations. Then, an optimization approach</p> <p>using the Response Surface Method (RSM) is conducted to minimize the annualized</p> <p>cost of the Hybrid Energy Storage System (HESS); consisting of a flywheel, supercapacitor, and battery. The goal is to smooth out the output power fluctuations by the optimal</p> <p>size of the HESS. Thus, a 1.5 MW hydraulic wind turbine is simulated, and the HESS is</p> <p>configured and optimized. The direct connection of the flywheel allows reaching a suitable</p> <p>level of smoothness at a reasonable cost. The proposed configuration is compared with the</p> <p>conventional storage, and the results demonstrate that the proposed integrated HESS can</p> <p>decrease the annualized storage cost by 71 %.</p> <p>Finally, this research investigates the effects of the reduced-size RSC on the Low Voltage</p> <p>Ride Through (LVRT) capabilities required from all wind turbines. One of the significant</p> <p>achievements of an SS-WECS is the reduced size excitation circuit. The grid side converter is</p> <p>eliminated, and the size of the rotor side converter (RSC) can be safely reduced to a fraction</p> <p>of a full-size excitation. Therefore, this low-power-rated converter operates at low voltage</p> <p>and handles the regular operation well. However, the fault conditions may expose conditions</p> <p>on the converter and push it to its limits. Therefore, four different protection circuits are</p> <p>employed, and their effects are investigated and compared to evaluate their performance.</p> <p>These four protection circuits include the active crowbar, active crowbar along a resistorinductor</p> <p>circuit (C-RL), series dynamic resistor (SDR), and new-bridge fault current limiter</p> <p>(NBFCL). The wind turbine controllers are also adapted to reduce the impact of the fault</p> <p>on the power electronic converters. One of the effective methods is to store the excess energy</p> <p>in the generator’s rotor. Finally, the proposed LVRT strategies are simulated in MATLAB</p> <p>Simulink to validate the results and demonstrate their effectiveness and functionality.</p>

Atualmente, a energia eólica é uma das fontes renováveis mais reconhecidas, e sua penetração em sistemas elétricos de potência está se incrementando consideravelmente. Por consequência, a participação de turbinas eólicas em sistemas elétricos de potência tem se incrementado e pode influenciar o comportamento geral do sistema de potência. Portanto, é importante estudar o desempenho de turbinas eólicas em sistemas elétricos e sua interação com outros equipamentos de geração e cargas. O principal objetivo nesta dissertação é determinar o desempenho dinâmico de diferentes tecnologias ligadas nos sistemas elétricos considerando diferentes níveis de penetração e diferentes perturbações elétricas mediante simulações realizadas usando um toolbox de Matlab/Simulink, SimPowerSystems. As tecnologias avaliadas são (a) o gerador de indução duplamente alimentado com fator de potência unitário, (b) o gerador de indução duplamente alimentado com controle de tensão, (c) o gerador de indução de gaiola de esquilo com compensação baseada em condensadores, e (d) gerador de indução de gaiola de esquilo sem equipamentos auxiliares. Os fatores técnicos analisados são perfil de tensão em estado estacionário, as dinâmicas durante afundamentos e elevações de tensão, correntes de curto circuito, e incremento gradual nas cargas do sistema, para verificar a estabilidade de tensão da rede para pequenas perturbações. É proposta uma estratégia para promover uma integração efetiva de turbinas eólicas em sistemas de potência com altos níveis de penetração considerando diferentes normas de operação da rede para sistemas de transmissão e de distribuição. O objetivo nesta estratégia é o cumprimento dos requisitos para conexão de rede com a combinação de tecnologias, minimizando o valor do investimento. Os efeitos na estabilidade de sistemas de potência da fazenda eólica determinada com a metodologia proposta são comparados com os efeitos de uma fazenda eólica de igual capacidade de energia eólica considerando somente geradores de indução duplamente alimentados com controle de tensão. Para as analises realizadas neste trabalho são considerados os sistemas IEEE de 9 e 30 barras. / Nowadays, wind power is one of the most accepted renewable energy sources, and its penetration in electrical power systems is increasing considerably. Consequently, the participation of wind turbines in electrical power systems has increased and may influence the overall power system behavior. It is therefore important to study the performance of wind turbines in electrical power systems and their interaction with other generation equipment and loads. The main objective of this dissertation is to determine the dynamic performance of different wind turbines technologies connected in electrical system considering different penetration levels and electrical perturbations by simulations performed using a Matlab/Simulink toolbox, SimPowerSystems. The assessed technologies are (a) double fed induction generator with unity power factor, (b) double fed induction generator with voltage control, (c) squirrel cage induction generator with capacitor-based compensation, and (d) squirrel cage induction generator without ancillary devices. The technical factors analyzed are steady-state voltage profile, the dynamics during voltage sags and swells, short-circuit currents, and gradual increase in the system loading, in order to check the network small-disturbance voltage stability. A strategy to promote an effective integration of wind turbines into the power systems with high levels of wind power penetration regarding different grid code requirements in transmission and distribution networks is proposed. The objective in this strategy is fulfilling the grid code requirements with a technology combination, minimizing the invested value. The effects on power system stability of the wind farm, found by the proposed methodology, are compared with the effects that have the same installed capacity of wind power but only considering double fed induction generators with voltage control. The IEEE 9 bus transmission system and the IEEE 30 bus system are regarded for the analysis performed in this work.

Atualmente, a energia eólica é uma das fontes renováveis mais reconhecidas, e sua penetração em sistemas elétricos de potência está se incrementando consideravelmente. Por consequência, a participação de turbinas eólicas em sistemas elétricos de potência tem se incrementado e pode influenciar o comportamento geral do sistema de potência. Portanto, é importante estudar o desempenho de turbinas eólicas em sistemas elétricos e sua interação com outros equipamentos de geração e cargas. O principal objetivo nesta dissertação é determinar o desempenho dinâmico de diferentes tecnologias ligadas nos sistemas elétricos considerando diferentes níveis de penetração e diferentes perturbações elétricas mediante simulações realizadas usando um toolbox de Matlab/Simulink, SimPowerSystems. As tecnologias avaliadas são (a) o gerador de indução duplamente alimentado com fator de potência unitário, (b) o gerador de indução duplamente alimentado com controle de tensão, (c) o gerador de indução de gaiola de esquilo com compensação baseada em condensadores, e (d) gerador de indução de gaiola de esquilo sem equipamentos auxiliares. Os fatores técnicos analisados são perfil de tensão em estado estacionário, as dinâmicas durante afundamentos e elevações de tensão, correntes de curto circuito, e incremento gradual nas cargas do sistema, para verificar a estabilidade de tensão da rede para pequenas perturbações. É proposta uma estratégia para promover uma integração efetiva de turbinas eólicas em sistemas de potência com altos níveis de penetração considerando diferentes normas de operação da rede para sistemas de transmissão e de distribuição. O objetivo nesta estratégia é o cumprimento dos requisitos para conexão de rede com a combinação de tecnologias, minimizando o valor do investimento. Os efeitos na estabilidade de sistemas de potência da fazenda eólica determinada com a metodologia proposta são comparados com os efeitos de uma fazenda eólica de igual capacidade de energia eólica considerando somente geradores de indução duplamente alimentados com controle de tensão. Para as analises realizadas neste trabalho são considerados os sistemas IEEE de 9 e 30 barras. / Nowadays, wind power is one of the most accepted renewable energy sources, and its penetration in electrical power systems is increasing considerably. Consequently, the participation of wind turbines in electrical power systems has increased and may influence the overall power system behavior. It is therefore important to study the performance of wind turbines in electrical power systems and their interaction with other generation equipment and loads. The main objective of this dissertation is to determine the dynamic performance of different wind turbines technologies connected in electrical system considering different penetration levels and electrical perturbations by simulations performed using a Matlab/Simulink toolbox, SimPowerSystems. The assessed technologies are (a) double fed induction generator with unity power factor, (b) double fed induction generator with voltage control, (c) squirrel cage induction generator with capacitor-based compensation, and (d) squirrel cage induction generator without ancillary devices. The technical factors analyzed are steady-state voltage profile, the dynamics during voltage sags and swells, short-circuit currents, and gradual increase in the system loading, in order to check the network small-disturbance voltage stability. A strategy to promote an effective integration of wind turbines into the power systems with high levels of wind power penetration regarding different grid code requirements in transmission and distribution networks is proposed. The objective in this strategy is fulfilling the grid code requirements with a technology combination, minimizing the invested value. The effects on power system stability of the wind farm, found by the proposed methodology, are compared with the effects that have the same installed capacity of wind power but only considering double fed induction generators with voltage control. The IEEE 9 bus transmission system and the IEEE 30 bus system are regarded for the analysis performed in this work.

Made available in DSpace on 2017-07-10T16:41:35Z (GMT). No. of bitstreams: 1 Dissert Milton Ernesto Barrios Aguilar 3.pdf: 9539969 bytes, checksum: 3ccd249e45fb24533b33236925ee74dc (MD5) Previous issue date: 2016-08-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The increase in wind power integration into power systems is currently a general trend in many countries and the Variable-Speed Wind Turbine (VSWT) Equipped with a Doubly Fed Induction Generator System with back-to-back power converters are most often used for this purpose. There is the need for its control system to operate properly to ensure stability and to achieve the desired performance when they are subjected to different transient disturbances, which is a difficult taste due to nonlinearities and strong coupling between electrical and mechanical variables in this type of wind turbine. In this context, this work aims to tune the gains of the PI controllers that make up the control system using a collective intelligence meta-heuristic algorithm for two normal perturbations in the operation of a wind farm: a wind variation and electrical fault. For that, it was modeled the wind turbine taking advantage of detailed modeling, considering the stator voltage oriented control structure, with active and reactive power control loops and their respective current controls, all equipped with PI controllers. Therefore, a set of objective functions was generated penalizing the most important variables directly from the dynamic simulation. Next, a multi-objective PSO algorithm has been enhanced, to be used as a tuning tool. Then the algorithm was applied to the VSWT for Single-machine infinite bus system for wind speed variation and electrical fault. Finally, the robustness of the tunings was tested on the in Single-machine infinite bus system and a 32 nodes feeder. The PSO showed good ability to exploitation and intensification of the search space reaching the preset tuning requirements in all cases. Stability and satisfactory performance results were obtained for transient disturbances thanks to key variables penalty in the objective functions. The tuning resulted robust enough for variations of feeder parameters and operating conditions besides the proper stiffness coefficient of the turbine generator mechanical coupling, whenever the wind turbine was subjected to disturbances considered in the tuning. It is also noted that exploring the objective functions and the algorithm itself can attain a large improvement in the performance of the tuned wind turbine control system for wind variations and electrical faults / O aumento da integração da geração eólica em sistemas elétricos de potência é atualmente uma tendência generalizada em muitos países e os Aerogeradores de Velocidade Variáveis (AVV) com Geradores de Indução de Dupla Alimentação (DFIG) com conversores de potência de tipo back-to-back são os mais empregados para este fim. Existe a necessidade de que seu sistema de controle atue corretamente para garantir a estabilidade e obter o desempenho desejado quando estes são submetidos a diferentes perturbações transitórias, o que resulta difícil devido às não-linearidades e à forte relação entre as grandezas elétricas e mecânicas deste tipo de aerogerador. Neste contexto, esta dissertação tem como objetivo a sintonia dos ganhos dos controladores PI que compõem o sistema de controle, utilizando um algoritmo meta-heurístico de inteligência coletiva, para duas perturbações normais na operação de uma usina eólica: variação de vento e falta elétrica. Para isso, foi modelado o DFIG aproveitando modelos detalhados, considerando a estrutura de controle orientada pela tensão do estator, com malhas de controle de potência ativa e reativa e seus respetivos controles de correntes, todas equipadas com controladores tipo PI. Logo foi gerado um conjunto de funções objetivos, penalizando diretamente das simulação dinâmica as variáveis de maior importância. A seguir, foi aprimorado um algoritmo PSO multi-objetivo, o qual é utilizado como ferramenta de sintonia. Em seguida, o algoritmo foi aplicado ao DFIG na configuração máquina barra-infinita para variação de vento e falta elétrica. Finalmente foi testada a robustez das sintonias obtidas no sistema de máquina barra-infinita e em um alimentador de 32 nós. O PSO apresentou uma boa capacidade de exploração e intensificação do espaço de busca alcançando os requisitos de sintonia preestabelecidos em todos os casos. Os resultados de estabilidade e desempenhos foram satisfatórios para as perturbações transitórias utilizadas graças à penalização de variáveis chaves nas funções objetivos. A sintonia resultou suficientemente robusta para variações de parâmetros do alimentador e de condições operativas, além do próprio coeficiente de rigidez do acoplamento mecânico turbina-gerador, sempre que a usina esteja submetida a perturbações consideradas na sintonia. Observa-se também que explorando as funções objetivo e o próprio algoritmo pode-se atingir uma ampla melhoria no desempenho do sistema de controle do DFIG sintonizado para as variações de vento e faltas elétricas. Palavras-chave: Geração Eólica, Aerogeradores

Made available in DSpace on 2017-07-10T17:11:51Z (GMT). No. of bitstreams: 1 MARCOS GUILHERME ZANCHETTIN.pdf: 1368217 bytes, checksum: 2ad7e15a270a9abefc8d6f85f3ba01e0 (MD5) Previous issue date: 2012-04-25 / The wind generation has stood out among the alternative sources and has experienced a high rate of penetration through the years. Thus, the electrical connection of wind power generation must be analyzed in detail to avoid or minimize the problems inherent this type of source can cause in electric power systems (SEP) and thereby preserve the voltage quality indicators and reliability. This paper deal about the integration of wind farms in SEP, equipped with squirrel-cage induction generator based fixed speed wind turbines (AVV-SCIG) and doublyfed induction generator based variable speed wind turbines (AVV-DFIG). The limits of integration of wind energy generation, i.e., the amount of power that the wind farm can provide the point-of-common-connection (PCC) while complying with certain interconnections requirements, are obtained considering static and transient aspects of the connection of wind farms. The topology adopted to represent, in a simplified way, the local characteristics of the connection between the wind farm and the SEP, as well as characterize the integration of wind generation from the parameters of the PCC, is the single machine infinite-bus system (MBI). Throughout the text also are presents the models used to represent the wind turbine and wind farm in studies of power systems, the main criteria specified to connection of this type of source in SEP and the main issues dealing with the problem of integration of generation wind. The analyzes aim to assess how the wind energy generation is impacted by technical criteria that consider static and transient aspects of the connection of wind farms, the technology used in energy conversion, the control strategy/operation and the characteristics of PCC. The results obtained allow to define which the stricts conditions for the integration of wind energy generation. For these analyzes are considered the criteria of the maximum allowable voltage variation at the connection point of the wind farm, the power range for the maximum transferable power to the electrical system and the fault ride through capability. / A geração eólica vem se destacando entre as fontes alternativas e tem experimentado um elevado índice de pene- tração ao longo dos anos. Assim, a conexão elétrica de parques eólicos precisa ser analisada detalhadamente a fim de evitar ou minimizar os efeitos que os problemas inerentes desse tipo de fonte, geração eólica, podem causar em sistemas elétrico de potência (SEP) e com isso preservar os indicadores de qualidade de tensão e confiabilidade. Este trabalho trata da integração de centrais eólicas em SEP, equipadas com aerogeradores de velocidade fixa com gerador de indução de rotor em gaiola (AVF-SCIG) e aerogeradores de velocidade variável com gerador de indução duplamente alimentado (AVV-DFIG). Os limites de inserção de geração eólica, i.e., a quantidade de potência que o parque eólico pode fornecer ao ponto comum de conexão (PCC) tendo que atender certos critérios da integração, são obtidos considerando aspectos estáticos e transitórios da conexão de centrais eólicas. A topologia adotada para representar, de maneira simplificada, as características locais de conexão entre o parque eólico e o SEP, assim como caracterizar a inserção de geração eólica a partir dos parâmetros do PCC, é o modelo máquina barra-infinita (MBI). Ao longo do texto também são apresentados os modelos empregados para representar tanto o aerogerador quanto o parque eólico em estudos de sistemas de potência, os principais critérios especificados para a conexão desse tipo de fonte em SEP e as principais questões que tratam do problema de inserção de geração eólica. As análises têm por objetivo avaliar como a inserção de geração eólica é impactada por critérios técnicos que consideram aspectos estáticos e transitórios da conexão de centrais eólicas, pela tecnologia empregada na conversão de energia, pela estratégia de controle/operação e pelas características do PCC. Os resultados obtidos permitem definir quais as condições mais severas à inserção de geração eólica. Para estas análises são considerados os critérios da máxima variação de tensão admissível no ponto de conexão da central eólica, a margem de potência relativamente à máxima potência transferível ao sistema elétrico e a capacidade de sustentação durante faltas.

High penetration of wind energy requires innovations in different areas of power engineering. Methods for improving wind energy and power system interconnection, control, and operation are proposed in this dissertation. A feed-forward transient compensation control scheme is proposed to enhance the low-voltage ride-through capability of wind turbines equipped with doubly fed induction generators. Stator-voltage transient compensation terms are introduced to suppress rotor-current overshoots and torque ripples during grid faults. A dynamic stochastic optimal power flow control scheme is proposed to optimally reroute real-time active and reactive power flow in the presence of high variability and uncertainty. The performance of the proposed power flow control scheme is demonstrated in test power systems with large wind plants. A combined energy-and-reserve wind market scheme is proposed to reduce wind production uncertainty. Variable wind reserve products are created to absorb part of the wind production variation. These fast wind reserve products can then be used to regulate system frequency and improve system security.

Η παρούσα διπλωματική εργασία πραγματεύεται την ανάλυση και σχεδίαση απευθείας ελέγχου πραγματικής και άεργου ισχύος σε αιολικό σύστημα με επαγωγική γεννήτρια διπλής τροφοδοσίας (Doubly-Fed Induction Generator, DFIG). Κύριος σκοπός της εργασίας είναι η εξαγωγή ενός κατάλληλου δυναμικού μοντέλου του συστήματος, το οποίο περιέχει ως καταστάσεις τις ισχείς. Επιπλέον, μέσω του διανυσματικού ελέγχου με προσανατολισμό στην τάση του δικτύου (Voltage-Oriented Control, VOC) επιτυγχάνεται ο απευθείας έλεγχος των ισχύων χρησιμοποιώντας αναλογικό-ολοκληρωτικούς (Proportional-Integral, PI) ελεγκτές, επιβάλλοντας με αυτόν τον τρόπο την επιθυμητή μεταβατική συμπεριφορά. Τελικά, η ανάλυση και η συμπεριφορά του αιολικού συστήματος επιβεβαιώνεται με τα αποτελέσματα της εξομοίωσης σε περιβάλλον MATLAB/Simulink. Ειδικότερα, στο κεφάλαιο 1 παρουσιάζονται το ενεργειακό πρόβλημα και τα διάφορα είδη ανανεώσιμων πηγών ενέργειας. Στο κεφάλαιο 2 αναφέρονται τα συστήματα αιολικής ενέργειας. Πιο συγκεκριμένα, περιγράφονται οι κυριότεροι τύποι ανεμογεννητριών και η δομή της, οι γεννήτριες και οι συσκευές ηλεκτρονικών ισχύος που χρησιμοποιούνται σε ένα αιολικό σύστημα, καθώς και ο μηχανικός έλεγχος ισχύος που μπορεί να εφαρμοστεί. Στη συνέχεια, στο κεφάλαιο 3 πραγματοποιείται η ανάλυση του αιολικού συστήματος με την DFIG όπου εξάγεται με την βοήθεια του μετασχηματισμού Park, το ζητούμενο μαθηματικό μοντέλο. Έπειτα, στο κεφάλαιο 4 αναφέρονται οι μέθοδοι ελέγχου που χρησιμοποιούνται στις ανεμογεννήτριες, εφαρμόζεται ο VOC στο αιολικό σύστημα που μελετάται και σχεδιάζονται οι απαιτούμενοι ελεγκτές PI ώστε να ελεγχθεί η ισχύς μέσω των δύο μετατροπέων ισχύος. Τέλος, στο κεφάλαιο 5 παρουσιάζεται η εξομοίωση του συστήματος και τα αποτελέσματα που προέκυψαν. / This diploma thesis deals with the analysis and design of a direct active and reactive power control system for a Doubly-Fed Induction Generator (DFIG) wind power system. The main purpose of this thesis is to extract a suitable dynamic model of the system that contains as states the active and reactive power. In addition, the direct control of the active and reactive power is achieved through voltage-oriented control (VOC) and the use of PI controllers, imposing the desirable transient behavior. Finally, the analysis and the performance of the wind system are verified through simulation results in MATLAB/Simulink. Specifically, in chapter 1 the energy problem and the different types of renewable energy sources are presented. The second chapter deals with the wind energy systems. In particular, the main types and the structure of wind turbines, the generators, the power electronic devices and the mechanic power control used in a wind power system are presented. Then, in chapter 3 the DFIG wind system is analysed and the required mathematical model is extracted using Park’s transformation. Next, in the fourth chapter the control methods for a wind turbine are presented and, using the VOC in the wind power system studied, the required PI controllers for the two power converters are designed. Finally, in chapter 5 the simulation results are presented and conclusions are drawn.

With the increasing complexity of the power system, electromechanical oscillations are becoming one of the major problem. Several blackouts have been reported in the past due to insufficient damping of the oscillatory modes. The starting point to avoid catastrophic behaviors would be to simulate actual power system and study the response of the system under various outages leading to blackouts. Recently, it has been identified that appropriate modeling of the load is necessary to match the actual system behavior with the computer simulated response. This research throws some insight into the detailed load modeling and its impact on the system small signal stability. In particular, Composite load model is proposed and its effect on the system small signal stability is investigated. Modeling all the loads in a large power system would be a cumbersome job and hence the method for identifying the most sensitive load location is also proposed in the thesis. The effect of load modeling on the eigenvalue movement is also investigated. The low damped electromechanical modes are always undesirable in the large inter-connected power systems as they might get excited under some event leading to growing oscillations. Proper damping of these modes is essential for effective and reliable system operation. Power system stabilizers have been proved to be an effective way of damping these electromechanical modes. The optimal number and location of PSS to effectively damp the modes via improved Differential algorithm is proposed. Moreover, the effect of TCSC, series compensated FACTs device, on enhancing the system damping is investigated. A fixed order model matching technique is presented to design a damping controller for the TCSC. With the increasing global pressure for reducing carbon emissions, there is a great amount of interest in the renewable sources of energy, particularly Wind Energy Conversion Systems. Of all the present methods of wind generation systems, Doubly Fed Induction Generation (DFIG) based wind farms are gaining popularity. The comparison of various methods of wind generation techniques is presented. In particular, the impact of DFIG based wind farms on the system small signal stability is investigated in this work. Co-ordinated tuning of the controllers is performed using Bacterial Foraging Technique, which is another member of Evolutionary algorithms. Damping controller for the DFIG system is proposed to enhance the damping of the electromechanical modes. Results have proved the effectiveness of the control methodology. The contributions made in this thesis could be utilized to promote the further development of the damping controllers for large power systems.

With the increasing complexity of the power system, electromechanical oscillations are becoming one of the major problem. Several blackouts have been reported in the past due to insufficient damping of the oscillatory modes. The starting point to avoid catastrophic behaviors would be to simulate actual power system and study the response of the system under various outages leading to blackouts. Recently, it has been identified that appropriate modeling of the load is necessary to match the actual system behavior with the computer simulated response. This research throws some insight into the detailed load modeling and its impact on the system small signal stability. In particular, Composite load model is proposed and its effect on the system small signal stability is investigated. Modeling all the loads in a large power system would be a cumbersome job and hence the method for identifying the most sensitive load location is also proposed in the thesis. The effect of load modeling on the eigenvalue movement is also investigated. The low damped electromechanical modes are always undesirable in the large inter-connected power systems as they might get excited under some event leading to growing oscillations. Proper damping of these modes is essential for effective and reliable system operation. Power system stabilizers have been proved to be an effective way of damping these electromechanical modes. The optimal number and location of PSS to effectively damp the modes via improved Differential algorithm is proposed. Moreover, the effect of TCSC, series compensated FACTs device, on enhancing the system damping is investigated. A fixed order model matching technique is presented to design a damping controller for the TCSC. With the increasing global pressure for reducing carbon emissions, there is a great amount of interest in the renewable sources of energy, particularly Wind Energy Conversion Systems. Of all the present methods of wind generation systems, Doubly Fed Induction Generation (DFIG) based wind farms are gaining popularity. The comparison of various methods of wind generation techniques is presented. In particular, the impact of DFIG based wind farms on the system small signal stability is investigated in this work. Co-ordinated tuning of the controllers is performed using Bacterial Foraging Technique, which is another member of Evolutionary algorithms. Damping controller for the DFIG system is proposed to enhance the damping of the electromechanical modes. Results have proved the effectiveness of the control methodology. The contributions made in this thesis could be utilized to promote the further development of the damping controllers for large power systems.