The study started with the requirement that a photovoltaic (PV) power source should be integrated with other supplementary power sources whether it operates in a stand-alone or grid-connected mode. First, fuel cells for a backup of varying PV power were compared in detail with batteries and were found to have more operational benefits. Next, maximizing performance of a grid-connected PV-fuel cell hybrid system by use of a two-loop controller was discussed. One loop is a neural network controller for maximum power point tracking, which extracts maximum available solar power from PV arrays under varying conditions of insolation, temperature, and system load. A real/reactive power controller (RRPC) is the other loop. The RRPC meets the system's requirement for real and reactive powers by controlling incoming fuel to fuel cell stacks as well as switching control signals to a power conditioning subsystem. The RRPC is able to achieve more versatile control of real/reactive powers than the conventional power sources since the hybrid power plant does not contain any rotating mass. Results of time-domain simulations prove not only effectiveness of the proposed computer models of the two-loop controller, but also their applicability for use in transient stability analysis of the hybrid power plant. Finally, environmental evaluation of the proposed hybrid plant was made in terms of plant's land requirement and lifetime CO2 emissions, and then compared with that of the conventional fossil-fuel power generating forms. / Ph. D.

Com o advento da geração distribuída foi permitido aos sistemas de distribuição a possibilidade de operação de forma ilhada dos sistemas interligados de grande porte. Apesar de suas vantagens, do ponto de vista técnico, ainda existe uma série de desafios que necessitam ser superados para a plena aplicação desse conceito. Um desses desafios é definido pela transição dos modos operativos dos geradores distribuídos durante o processo de ilhamento. Da forma em que é reportada na literatura, infere-se que tal transição é realizada de um modo inadequado, amplificando os transitórios observados nas grandezas do gerador distribuído - e por consequência, da rede em que o mesmo se conecta - durante o processo de ilhamento, o que não é desejável. No contexto apresentado, a principal contribuição desta pesquisa está em propor uma estrutura híbrida de controle a ser aplicada aos sistemas de excitação de geradores síncronos que operam em sistemas de distribuição que permitem a operação ilhada de determinadas porções de suas redes. A principal característica da estrutura proposta está em atenuar os transitórios das variáveis do gerador controlado durante o processo de ilhamento. Além disso, o arranjo da estrutura proposta estabelece um compromisso entre a potência reativa e a tensão terminal do gerador controlado, quando o mesmo opera em paralelo com os sistemas interligados de grande porte. Nessa condição, o sistema de controle mantém a potência reativa próxima da referência ajustada atendendo a uma faixa adequada de valores de tensão terminal. / With the advent of distributed generation, the possibility of autonomous operation regarding the bulk power systems was allowed to the distribution systems. Despite its advantages, from the technical point of view, there are lots of challenges that need to be overcome for the full application of this concept. One of these challenges is the transition of distributed generators operating modes during the islanding process. Based in the literature survey, it is inferred that transition is performed in a wrong way, which amplifies the transients in controlled generator quantities and consequently, of the network connected to it during the islanding process, which is undesirable. In this context, the main contribution of this research is the proposal of a hybrid control structure to be applied to the excitation systems of synchronous generators that operate in distribution systems whose islanded operation of determined portions of its grids is permitted. The main characteristic of the proposed structure is the attenuation of transients of the controlled generator quantities during the islanding process. Furthermore, the design of this structure provides a compromise between the generator reactive power and terminal voltage when it operates in parallel with the bulk power systems. That way, the control system maintains the reactive power close to the adjusted reference attending an appropriate range of terminal voltage values.

Com o advento da geração distribuída foi permitido aos sistemas de distribuição a possibilidade de operação de forma ilhada dos sistemas interligados de grande porte. Apesar de suas vantagens, do ponto de vista técnico, ainda existe uma série de desafios que necessitam ser superados para a plena aplicação desse conceito. Um desses desafios é definido pela transição dos modos operativos dos geradores distribuídos durante o processo de ilhamento. Da forma em que é reportada na literatura, infere-se que tal transição é realizada de um modo inadequado, amplificando os transitórios observados nas grandezas do gerador distribuído - e por consequência, da rede em que o mesmo se conecta - durante o processo de ilhamento, o que não é desejável. No contexto apresentado, a principal contribuição desta pesquisa está em propor uma estrutura híbrida de controle a ser aplicada aos sistemas de excitação de geradores síncronos que operam em sistemas de distribuição que permitem a operação ilhada de determinadas porções de suas redes. A principal característica da estrutura proposta está em atenuar os transitórios das variáveis do gerador controlado durante o processo de ilhamento. Além disso, o arranjo da estrutura proposta estabelece um compromisso entre a potência reativa e a tensão terminal do gerador controlado, quando o mesmo opera em paralelo com os sistemas interligados de grande porte. Nessa condição, o sistema de controle mantém a potência reativa próxima da referência ajustada atendendo a uma faixa adequada de valores de tensão terminal. / With the advent of distributed generation, the possibility of autonomous operation regarding the bulk power systems was allowed to the distribution systems. Despite its advantages, from the technical point of view, there are lots of challenges that need to be overcome for the full application of this concept. One of these challenges is the transition of distributed generators operating modes during the islanding process. Based in the literature survey, it is inferred that transition is performed in a wrong way, which amplifies the transients in controlled generator quantities and consequently, of the network connected to it during the islanding process, which is undesirable. In this context, the main contribution of this research is the proposal of a hybrid control structure to be applied to the excitation systems of synchronous generators that operate in distribution systems whose islanded operation of determined portions of its grids is permitted. The main characteristic of the proposed structure is the attenuation of transients of the controlled generator quantities during the islanding process. Furthermore, the design of this structure provides a compromise between the generator reactive power and terminal voltage when it operates in parallel with the bulk power systems. That way, the control system maintains the reactive power close to the adjusted reference attending an appropriate range of terminal voltage values.

This work presents a dynamic model for utility-scale PV systems. The model is based on a centralized converter topology, which uses a voltage-sourced converter (VSC) to facilitate the exchange of energy between PV generators and the utility grid. The related control system regulates active and reactive power injected by the PV system, based on a current control strategy. Moreover, the model includes a Maximum Power Point Tracking (MPPT) scheme, implemented with the incremental conductance method. Dimensioning of the model is presented as well as simulation cases to validate its performance. Subsequently, the model was used to analyze the effect of variations in solar radiation on a test network with high penetration of photovoltaic generation. Results showed that without proper compensation of reactive power, variations in solar radiation can cause voltage fluctuations outside allowable limits. Thus, in order to mitigate these fluctuations, local control strategies were implemented to allow the exchange of reactive power between the solar farm and the utility grid. Simulations showed that the proposed strategies can mitigate voltage fluctuations at the point of common coupling, improving voltage regulation in the network. / Este trabalho apresenta um modelo dinâmico de sistemas fotovoltaicos de grande escala. O modelo é baseado em uma topologia de conversor centralizado, que usa um conversor de fonte de tensão (VSC) para facilitar a troca de energia entre os geradores fotovoltaicos e a rede elétrica. O sistema de controle relacionado regula a energia ativa e reativa injetada pelo sistema fotovoltaico, com base em uma estratégia de controle de corrente. Além disso, o modelo inclui um sistema de rastreamento de ponto de potência máxima (MPPT), implementado com o método da condutância incremental. O dimensionamento do modelo é apresentado, bem como vários casos de simulação para validar o seu desempenho. Posteriormente, o modelo foi utilizado para analisar o efeito das variações na radiação solar sobre uma rede de teste com uma elevada penetração de geração fotovoltaica. Os resultados mostraram que sem uma adequada compensação de energia reativa, as variações na radiação solar podem causar flutuações de tensão fora dos limites permitidos. Assim, a fim de mitigar estas flutuações, estratégias de controle local foram implementadas para permitir a troca de potência reativa entre os sistemas fotovoltaicos e a rede. As simulações mostraram que as estratégias propostas podem mitigar as flutuações de tensão no ponto de acoplamento comum, melhorando a regulação de tensão na rede.

This work presents a dynamic model for utility-scale PV systems. The model is based on a centralized converter topology, which uses a voltage-sourced converter (VSC) to facilitate the exchange of energy between PV generators and the utility grid. The related control system regulates active and reactive power injected by the PV system, based on a current control strategy. Moreover, the model includes a Maximum Power Point Tracking (MPPT) scheme, implemented with the incremental conductance method. Dimensioning of the model is presented as well as simulation cases to validate its performance. Subsequently, the model was used to analyze the effect of variations in solar radiation on a test network with high penetration of photovoltaic generation. Results showed that without proper compensation of reactive power, variations in solar radiation can cause voltage fluctuations outside allowable limits. Thus, in order to mitigate these fluctuations, local control strategies were implemented to allow the exchange of reactive power between the solar farm and the utility grid. Simulations showed that the proposed strategies can mitigate voltage fluctuations at the point of common coupling, improving voltage regulation in the network. / Este trabalho apresenta um modelo dinâmico de sistemas fotovoltaicos de grande escala. O modelo é baseado em uma topologia de conversor centralizado, que usa um conversor de fonte de tensão (VSC) para facilitar a troca de energia entre os geradores fotovoltaicos e a rede elétrica. O sistema de controle relacionado regula a energia ativa e reativa injetada pelo sistema fotovoltaico, com base em uma estratégia de controle de corrente. Além disso, o modelo inclui um sistema de rastreamento de ponto de potência máxima (MPPT), implementado com o método da condutância incremental. O dimensionamento do modelo é apresentado, bem como vários casos de simulação para validar o seu desempenho. Posteriormente, o modelo foi utilizado para analisar o efeito das variações na radiação solar sobre uma rede de teste com uma elevada penetração de geração fotovoltaica. Os resultados mostraram que sem uma adequada compensação de energia reativa, as variações na radiação solar podem causar flutuações de tensão fora dos limites permitidos. Assim, a fim de mitigar estas flutuações, estratégias de controle local foram implementadas para permitir a troca de potência reativa entre os sistemas fotovoltaicos e a rede. As simulações mostraram que as estratégias propostas podem mitigar as flutuações de tensão no ponto de acoplamento comum, melhorando a regulação de tensão na rede.

In this thesis, design and implementation of a distribution-type, voltage source converter (VSC) based static synchronous compensator (D-STATCOM) having the simplest converter and coupling transformer topologies have been carried out. The VSC STATCOM is composed of a +/- 750 kVAr full-bridge VSC employing selective harmonic elimination technique, a low-pass input filter, and a &amp / #8710 / /Y connected coupling transformer for connection to medium voltage bus. The power stage of VSC based STATCOM is composed of water-cooled high voltage IGBT modules switched at 850 Hz for the elimination of 5th, 7th, 11th, 13th, 17th, 19th, 23rd,and 25th voltage harmonics. Special care has been taken in the laminated busbar design to minimize stray inductances between power semiconductors and dc link capacitor. Reactive power control is achieved by applying the phase angle control technique. The effect of input filter on total demand distortion has been investigated theoretically by mathematical derivations. The proposed VSC STATCOM has been implemented for reactive power compensation of Coal Preparation System in Kemerk&ouml / y Thermal Power Plant. The field test results have shown the success of the implemented system in view of fast response in reactive power compensation, and minimum input current harmonic content, and compliance with the IEEE Std. 519-1992 even for the weakest power systems. The application of selective harmonic elimination technique and phase angle control to VSC STATCOM has led to optimum switching frequency and device utilization for high voltage IGBTs at the expense of slower response as compared to other PWM techniques.

Long term supporting schemes for photovoltaic (PV) system installation have led to accommodating large numbers of PV systems within load pockets in distribution grids. High penetrations of PV systems can cause new technical challenges, such as voltage rise due to reverse power flow during light load and high PV generation conditions. Therefore, new strategies are required to address the associated challenges. Moreover, due to these changes in distribution grids, a different response behavior of the distribution grid on the transmission side can be expected. Hence, a new equivalent model of distribution grids with high penetration of PV systems is needed to be addressed for future power system studies. The thesis contributions lie in three parts. The first part of the thesis copes with the PV modelling. A non-proprietary PV model of a three-phase, single stage PV system is developed in PSCAD/EMTDC and PowerFactory. Three different reactive power regulation strategies are incorporated into the models and their behavior are investigated in both simulation platforms using a distribution system with PV systems. In the second part of the thesis, the voltage rise problem is remedied by use of reactive power. On the other hand, considering large numbers of PV systems in grids, unnecessary reactive power consumption by PV systems first increases total line losses, and second it may also jeopardize the stability of the network in the case of contingencies in conventional power plants, which supply reactive power. Thus, this thesis investigates and develops the novel schemes to reduce reactive power flows while still keeping voltage within designated limits via three different approaches: decentralized voltage control to the pre-defined set-points developing a coordinated active power dependent (APD) voltage regulation Q(P)using local signals developing a multi-objective coordinated droop-based voltage (DBV) regulation Q(V) using local signals   In the third part of the thesis, furthermore, a gray-box load modeling is used to develop a new static equivalent model of a complex distribution grid with large numbers of PV systems embedded with voltage support schemes. In the proposed model, variations of voltage at the connection point simulate variations of the model’s active and reactive power. This model can simply be integrated intoload-flow programs and replace the complex distribution grid, while still keepingthe overall accuracy high. The thesis results, in conclusion, demonstrate: i) using rms-based simulations in PowerFactory can provide us with quite similar results using the time domain instantaneous values in PSCAD platform; ii) decentralized voltage control to specific set-points through the PV systems in the distribution grid is fundamentally impossible dueto the high level voltage control interaction and directionality among the PV systems; iii) the proposed APD method can regulate the voltage under the steady-state voltagelimit and consume less total reactive power in contrast to the standard characteristicCosφ(P)proposed by German Grid Codes; iv) the proposed optimized DBV method can directly address voltage and successfully regulate it to the upper steady-state voltage limit by causing minimum reactive power consumption as well as line losses; v) it is beneficial to address PV systems as a separate entity in the equivalencing of distribution grids with high density of PV systems. / <p>The Doctoral Degrees issued upon completion of the programme are issued by Comillas Pontifical University, Delft University of Technology and KTH Royal Institute of Technology. The invested degrees are official in Spain, the Netherlands and Sweden, respectively. QC 20141028</p>

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The purpose of this work is to present an active and reactive power flow controller applied to inverter paralelism with the stiff AC system. An additional loop is implemented into a conventional control loop based on the characteristic curves of active power versus frequency and reactive power versus voltage. This loop uses the active power variation as feedback to generate the load angle of the voltage reference of the inverter, when it is connected in parallel with the electric network. As a consequence, the active and reactive transitory power oscillations are atenuated, without producing undesirable colateral effects as significative voltage and reactive power variations presented in the utilization of PSS (Power System Stabilizer), another technique used to improve the system damping, [Martins, M. P., 2004]. A dynamic model of the system based on the small signal analysis is presented. The root locus graphics, showing the system poles under parametric variations are also presented, allowing the analysis of the system stability. The simulation results and the experimental ones using a laboratory prototype with and without the additional loop are showed, which validate the obtained small signal model. / Este trabalho apresenta um controlador de fluxos de potência ativa e reativa aplicado ao paralelismo de um inversor com a rede elétrica. Uma malha adicional de controle é inserida a um controlador convencional, o qual é baseado nas curvas características de potência ativa versus freqüência e potência reativa versus tensão. Essa malha utiliza a realimentação da própria variação da potência ativa para a geração do ângulo de carga da tensão de referência do inversor, quando o mesmo é conectado em paralelo com a rede elétrica. Como resultado as oscilações transitórias das potências ativa e reativa são melhor atenuadas, sem produzir efeitos colaterais indesejáveis tais como as variações de tensão e potência reativa presentes na utilização do PSS (Power System Stabilizer Estabilizador de Sistemas de Potência), outra técnica usada para melhorar o amortecimento do sistema, [Martins, M. P., 2004]. Um modelo dinâmico do sistema baseado na análise para pequenos sinais é apresentado. Gráficos do lugar das raízes, mostrando os pólos do sistema diante de variações paramétricas também são apresentados, permitindo a análise de estabilidade do sistema. Resultados de simulação e resultados experimentais utilizando-se um protótipo de laboratório, com e sem a malha de realimentação adicional são mostrados, os quais validam o modelo para pequenos sinais obtido. / Doutor em Ciências

Orientador: Edson Bim / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-06T02:49:03Z (GMT). No. of bitstreams: 1 Segnini_HelioHenriquedeAgostini_M.pdf: 1646244 bytes, checksum: d03ec95486ccbccae70ffedf89d964f1 (MD5) Previous issue date: 2006 / Resumo: O objetivo deste trabalho é estudar o modelo da máquina de indução duplamente alimentada no sistema de referência síncrono, bem como controlar seu fluxo de potências através de orientação de fluxo. São analisadas as orientações de fluxo de estator, de entreferro e de rotor em várias operações: compensador de reativos, gerador e motor, com fator de potência indutivo, capacitivo e unitário, nas faixas de velocidade subsíncrona, síncrona e supersíncrona / Abstract: The purpose of this work is to study the Doubly Fed Induction Machine modeling at the synchronous reference frame, as well as to control its power flux by flux oriented control The stator, rotor and air gap flux orientations with the machine operating as reactive compensator, generator and drive, with lag power factor, lead power factor and unity power factor at subsynchronous, synchronous and supersynchronous speeds are analyzed. / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Orientador: Edson Bim / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-21T12:34:50Z (GMT). No. of bitstreams: 1 Jacomini_RogerioVani_D.pdf: 15030828 bytes, checksum: 7c0af103e9c6a3a9527e3c25e4373e7e (MD5) Previous issue date: 2012 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The abstract is available with the full electronic document / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica