Dentre as fontes de energia renováveis utilizadas para geração de energia elétrica a que mais se destaca atualmente e a energia eólica. 0 crescente índice de penetração da geração eólica na matriz energética dos sistemas de potencia impõe a necessidade da revisão de conceitos anteriormente estabelecidos sobre a estabilidade de sistemas de potencia, uma vez que ainda não e perfeitamente compreendida a influencia de uma maior integração deste recurso no comportamento dos sistemas de potencia. Este trabalho tem como foco o estudo da estabilidade de sistemas com aerogeradores de velocidade fixa equipados com geradores de indução de rotor em gaiola. E estudada a estabilidade angular de um sistema de geração eólica equipado com aerogeradores desta natureza. O problema da estabilidade foi decomposto em três partes: estabilidade estática, estabilidade dinâmica e estabilidade transitória. São definidos os modelos dos componentes do aerogerador para cada um dos estudos realizados. A topologia adotada á a máquina Barramento Infinito (MBI), na qual o restante do sistema de potência a representado pelo seu equivalente de Thevenin. Esta topologia típica de analise de estabilidade de sistemas de potencia e adotada por permitir a obtenção de resultados analíticos para as analises estática e dinâmica. A analise transitória se dá através de simulações computacionais. A fim de manter um caráter mais geral para os resultados as simulações são realizados com três aerogeradores de características distintas. Os resultados obtidos permitem uma melhor compreensão da influencia sobre a estabilidade do sistema de geração eólica dos parâmetros de rede do sistema de potencia como: potencia de curto-circuito do ponto de conexão comum com o sistema de potencia, relação X/R da linha de transmissão e do capacitor de compensação de fator de potencia. / Among the renewable energy sources used to generate electric power one of the most important at this time is the wind power. The growing penetration index of wind power in the power systems energetic matrix leads to the necessity of a reevaluation of the concepts previously established about the stability of power systems, since the influence of a major integration of this resource in the behavior of power systems is not perfectly understood. This work focuses on the stability study of wind power systems equiped with fixed-speed squirrel-cage induction generators. The angular stability of a wind generation system equipped with wind generators of this nature is studied. The stability problem was decomposed in three parts: static stability, dynamic stability and transient stability. The models of the components of the wind generator are defined for each of the studies. The considered topology was an Induction Generator Infinite Bus System (IBM), where the rest of the power system is represented by it’s Thévenin equivalent. This is a typical topology in power systems stability analysis and is adopted in this work aiming at obtaining analytical and general stability results. The transient analysis is performed by computer simulations. In order to provide more generatily to the stability results, all simulations are conducted with three wind generators with distinct characteristics. The obtained results allow a better comprehension about the influence, on the stability of wind power systems, of power system network parameters as: short-circuit capacity of the common connection point with the power system, the X/R relation of the transmission line and the power factor compensation capacitor.

With the rise in energy consumption and usage by an exploding human population and higher quality of life, it is time to switch to renewable energy sources that have lower impacts on the natural world. Commercial scale wind power has seen tremendous growth in the last two decades and is expected to continue growing. But small-scale wind power still has tremendous potential in creating energy efficient homes micro-grid systems. Through this work, we explore the potential of micro VAWTs installed on highway medians to capture wind energy from moving vehicles. There are 2 main questions intended to be addressed here, namely: Is energy production from vehicular wake losses significant and if significant, how does the produced energy stand in comparison to a household’s consumption as well as an LED streetlight. In order to proceed with this work, we have taken the reference wind measurements performed on highway medians in Malaysia from literature. The right turbine choice for this application has also been contemplated through the literature review and chosen to be a cross-flow VAWT model with experimental results.Using the power curve of the turbine and the extracted wind speed measurements, energy production is estimated and compared to the electricity consumption of a suburban home in Malaysia. Further on, other analyses are performed to better understand the energy production potential of such applications and estimated for varying size in turbine, position of turbine with respect to ground, and the energy generation per kilometer of highway length.

A novel probabilistic method has been developed for modelling the operation of energy storage in electricity systems with significant amounts of wind and solar powered generation. This method is based on a spectral analysis of the variations of wind speed and solar irradiance together with profiles of electrical demand. The method has been embodied in two Matlab computer programs: Wind power only: This program models wind power on any time scale from seconds to years, with limited modelling of demand profiles. This program is only capable of modelling stand-alone systems, or systems in which the electrical demand is replaced by a weak grid connection with limited export capacity. 24-hours: This program models wind power, solar PV power and electrical demand, including seasonal and diurnal effects of each. However, this program only models store cycle times (variations within a time scale) of 24 hours. This program is capable of modelling local electrical demand at the same time as a grid connection with import or export capacity and a backup generator. Each of these programs has been validated by comparing its results with those from a time step program, making four Matlab programs in total. All four programs calculate the power flows to and from the store, satisfied demand, unsatisfied demand and curtailed power. The programs also predict the fractions of time that the store spends full, empty, filling or emptying. The results obtained are promising. Probabilistic program results agree well with time step results over a wide range of input data and time scales. The probabilistic method needs further refinement, but can be used to perform initial modelling and feasibility studies for renewable energy systems. The probabilistic method has the advantage that the required input data is less, and the computer run time is reduced, compared to the time step method.

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

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Na presente tese, propÃe-se um controlador robusto LQG/LTR (Linear Quadratic Gaussian with Loop Transfer Recovery) com aÃÃo integral (LQG/LTRI) em uma nova aplicaÃÃo para o ajuste dos controladores do conversor do lado da mÃquina e do conversor do lado rede elÃtrica em um sistema de conversÃo eÃlica utilizando um gerador de induÃÃo duplamente alimentado (Doubly-Fed Induction Generator - DFIG). A metodologia de controle proposta assegura a robustez em relaÃÃo à rejeiÃÃo do erro de rastreamento, insensibilidade a variaÃÃes paramÃtricas, alÃm de permitir que erros de medida e modelagem sejam incorporados no projeto. Testes de robustez e desempenho foram realizados para variaÃÃes dos parÃmetros internos da mÃquina e variaÃÃes de referÃncia de velocidade. Resultados de simulaÃÃo e experimentais, obtidos em um protÃtipo de laboratÃrio com uma mÃquina de 2kW sÃo apresentados para validar e demonstrar o bom desempenho e robustez do controlador proposto comparado com os controladores clÃssicos Proporcional-Integral (PI) em um sistema de geraÃÃo eÃlica com mÃquinas DFIG. / It is proposed in this thesis a LQG/LTR robust controller (Linear Quadratic Gaussian with Loop Transfer Recovery) with integral action (LQG/LTRI) in a new application for gain tuning for the rotor side converter and grid side converter in a wind energy conversion system (WECS) with Doubly-Fed Induction Generator(DFIG). The proposed control method assures the robustness with respect to the tracking error rejection, insensitivity to parameter variations and permits that measurement and modeling errors are incorporated in the project. Robustness and performance tests were performed for variations of machine internal parameters and speed. Simulation and experimental results, obtained from a laboratory prototype that uses a 2 kW machine are presented to validate and demonstrate the robustness and performance of the proposed controller through the comparison with the proportional and integral (PI) controller employed in a wind energy conversion system with DFIG.

Nesta tese apresenta-se o desenvolvimento de diversos modelos computacionais de turbinas eólicas equipadas com diferentes tipos de geradores elétricos, com ênfase no gerador de indução duplamente alimentado. Tais modelos foram desenvolvidos para investigar o desempenho de diferentes estratégias de controle, bem como diferentes estratégias do uso do sistema de proteção do conversor AC/DC/AC. Desenvolveu-se adicionalmente um método analítico para investigar a estabilidade de geradores de indução duplamente alimentados durante grandes perturbações na rede elétrica. Tal método foi validado por meio de comparações entre os resultados da aplicação das fórmulas propostas e de simulações, utilizando uma simplificação dos modelos dinâmicos desenvolvidos. Considerando os modelos dinâmicos, os resultados obtidos por simulações mostram que as escolhas adequadas da estratégia de controle e do sistema de proteção permitem maior injeção de potência reativa durante curto-circuitos na rede elétrica. O método analítico proposto apresentou resultados suficientemente precisos para análise da estabilidade frente a grandes perturbações, reduzindo o esforço necessário para realização de simulações dinâmicas sem a necessidade de compra de licenças de programas específicos. / The development of computational models of wind turbines equipped with different electrical machines is presented in this thesis, emphasizing the doubly fed induction generator. Such models were developed to investigate the performance of different control strategies as well as different protection system of the back-to-back converters. Additionally, this thesis present an original analytic method to investigate the stability of doubly fed induction generators during large disturbance on the electric system. The methodology is validated by comparing results from the developed dynamic models to the results from the analytical equations. For the dynamic models, the obtained results by simulations show that the chosen of the appropriate control strategies and the protection system can permit more reactive power injection during short circuits in the network. The proposed analytic method is sufficiently precise to analyze large disturbance stability reducing the necessary effort spending on dynamic simulation without the need of buying a specific license to run the software.

Com o aumento da penetração da energia eólica nos sistemas de potência, critérios cada vez mais rigorosos vem sendo estabelecidos ao longo do tempo para a conexão e operação das plantas eólicas nas redes elétricas. A evolução das tecnologias empregadas em turbinas possibilitou o atendimento a esses critérios, passando do conceito dinamarquês de turbinas de velocidade fixa para turbinas de velocidade variável, que possibilitam melhor aproveitamento da energia disponível nos ventos e maior capacidade de controle das grandezas envolvidas. Neste trabalho, foram analisados diferentes tipos de controle de um gerador de indução duplamente alimentado (DFIG) e a influência dessa máquina nos níveis de tensão de uma rede de subtransmissão à qual está conectada. Os resultados mostram que os tipos de controles indicados para a operação da planta eólica podem variar sensivelmente de acordo com o carregamento e a velocidade do vento em um determinado momento. O crescimento de carga esperado da rede também pode influenciar na estratégia de controle da planta. / With the increased penetration of wind energy in electrical power systems, increasingly stringent grid codes have been stablished over time for the connection and operation of wind power plants. The evolution of the technologies applied in wind turbines allowed meeting these criteria, moving from the Danish concept of fixed-speed turbines to variable-speed wind turbines, which enable better use of the available wind power and greater control of the variables involved. This study analyzes different control strategies of a doubly-fed induction generation (DFIG) and the influence of this machine in the voltage profile of a subtransmission system to which it is connected. The results show that the types of control suitable for the operation of the wind power plant may vary considerably according to the load and the wind speed at a given time. The expected load growth of the network can also influence in power plant control strategy.

Com o aumento da penetração da energia eólica nos sistemas de potência, critérios cada vez mais rigorosos vem sendo estabelecidos ao longo do tempo para a conexão e operação das plantas eólicas nas redes elétricas. A evolução das tecnologias empregadas em turbinas possibilitou o atendimento a esses critérios, passando do conceito dinamarquês de turbinas de velocidade fixa para turbinas de velocidade variável, que possibilitam melhor aproveitamento da energia disponível nos ventos e maior capacidade de controle das grandezas envolvidas. Neste trabalho, foram analisados diferentes tipos de controle de um gerador de indução duplamente alimentado (DFIG) e a influência dessa máquina nos níveis de tensão de uma rede de subtransmissão à qual está conectada. Os resultados mostram que os tipos de controles indicados para a operação da planta eólica podem variar sensivelmente de acordo com o carregamento e a velocidade do vento em um determinado momento. O crescimento de carga esperado da rede também pode influenciar na estratégia de controle da planta. / With the increased penetration of wind energy in electrical power systems, increasingly stringent grid codes have been stablished over time for the connection and operation of wind power plants. The evolution of the technologies applied in wind turbines allowed meeting these criteria, moving from the Danish concept of fixed-speed turbines to variable-speed wind turbines, which enable better use of the available wind power and greater control of the variables involved. This study analyzes different control strategies of a doubly-fed induction generation (DFIG) and the influence of this machine in the voltage profile of a subtransmission system to which it is connected. The results show that the types of control suitable for the operation of the wind power plant may vary considerably according to the load and the wind speed at a given time. The expected load growth of the network can also influence in power plant control strategy.

Nesta tese apresenta-se o desenvolvimento de diversos modelos computacionais de turbinas eólicas equipadas com diferentes tipos de geradores elétricos, com ênfase no gerador de indução duplamente alimentado. Tais modelos foram desenvolvidos para investigar o desempenho de diferentes estratégias de controle, bem como diferentes estratégias do uso do sistema de proteção do conversor AC/DC/AC. Desenvolveu-se adicionalmente um método analítico para investigar a estabilidade de geradores de indução duplamente alimentados durante grandes perturbações na rede elétrica. Tal método foi validado por meio de comparações entre os resultados da aplicação das fórmulas propostas e de simulações, utilizando uma simplificação dos modelos dinâmicos desenvolvidos. Considerando os modelos dinâmicos, os resultados obtidos por simulações mostram que as escolhas adequadas da estratégia de controle e do sistema de proteção permitem maior injeção de potência reativa durante curto-circuitos na rede elétrica. O método analítico proposto apresentou resultados suficientemente precisos para análise da estabilidade frente a grandes perturbações, reduzindo o esforço necessário para realização de simulações dinâmicas sem a necessidade de compra de licenças de programas específicos. / The development of computational models of wind turbines equipped with different electrical machines is presented in this thesis, emphasizing the doubly fed induction generator. Such models were developed to investigate the performance of different control strategies as well as different protection system of the back-to-back converters. Additionally, this thesis present an original analytic method to investigate the stability of doubly fed induction generators during large disturbance on the electric system. The methodology is validated by comparing results from the developed dynamic models to the results from the analytical equations. For the dynamic models, the obtained results by simulations show that the chosen of the appropriate control strategies and the protection system can permit more reactive power injection during short circuits in the network. The proposed analytic method is sufficiently precise to analyze large disturbance stability reducing the necessary effort spending on dynamic simulation without the need of buying a specific license to run the software.

The wind turbine generation system (WTGS) exhibits a nonlinear characteristic and its maximum power point varies with changing atmospheric conditions. In order to operate the WTGS at maximum power output under various wind speeds and to avoid using speed encoder in practical applications, it is necessary to improve the controller system to operate the maximum power points in the WTGS. There are three factors to influence wind generator, the wind speed, power coefficient and the radius of blade. The power coefficient depends on the blade pitch angle and tip speed ratio (TSR). The objective of the dissertation is to develop an intelligent controlled wind energy conversion system (WECS) using AC/DC and DC/AC power converters for grid-connected power application. To achieve a fast and stable response for the real power control, an intelligent controller was proposed, which consists of a fuzzy neural network (FNN), a recurrent fuzzy neural network (RFNN), a wilcoxcon radial basis function network (WRBFN) and a improved Elman neural network (IENN) for MPPT. Furthermore, the parameter of the developed FNN, RFNN, WRBFN and IENN are trained on-line using back-propagation learning algorithm. However, the learning rates in the FNN, RFNN, WRBFN, and IENN are usually selected by trial and error method, which is time-consuming. Therefore, modified particle swarm optimization (MPSO) method is adopted to adjust the learning rates to improve the learning capability of the developed RFNN, WRBFN and IENN. Moreover, presents the estimation of the rotor speed is based on the sliding mode and model reference adaptive system (MRAS) speed observer theory. Furthermore, a sensorless vector-control strategy for an induction generator (IG) operating in a grid-connected variable speed wind energy conversion system can be achieved. On the other hand, a WRBFN based with hill-climb searching (HCS) maximum-power-point-tracking (MPPT) strategy is proposed for permanent magnet synchronous generator (PMSG) with a variable speed wind turbine. Finally, many simulation results are provided to show the effectiveness of the proposed intelligent control wind generation systems.