Estudo da capacidade LVRT de sistemas eólicos com DFIG durante a ocorrência de faltas elétricas
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2020-06-01
Autores
Costa, Christielly Fernandes da
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Universidade Estadual Paulista (Unesp)
Resumo
Nos últimos anos, questões relacionadas ao meio ambiente, principalmente, ao uso de combustíveis fósseis e à emissão de gases poluentes na atmosfera, ganharam grande destaque internacional. Com os avanços da comunidade científica e o aumento no preço do petróleo no começo da década de 1970, o uso de fontes renováveis, não poluentes e limpas teve grande investimento por parte de diversos países. Nesse contexto, a geração eólica vem se destacando como uma das mais promissoras, especialmente devido a sua viabilidade econômica e ao seu rápido desenvolvimento tecnológico. Entre as diferentes topologias utilizadas nos sistemas de geração eólica, destaca-se a configuração elaborada para operação em velocidade variável, que emprega o gerador de indução duplamente alimentado (DFIG), associado ao conversor eletrônico back-to-back para controle de sua operação. Como principais vantagens da utilização do DFIG, destacam-se sua maior eficiência na conversão de energia, menor estresse mecânico do rotor, controle independente de potência ativa e reativa limitada a valores típicos de 30% da potência nominal. Por outro, sabe-se que, durante a ocorrência de um distúrbio, as correntes do rotor podem atingir altas magnitudes e causar danos ao conversor. Além disso, sobretensões no capacitor do elo CC ocorrem devido à perda de capacidade de transferência de energia do conversor do lado da rede. Entretanto, os aerogeradores podem ser requisitados a permanecerem em funcionamento mesmo durante uma falta, além de contribuírem para o restabelecimento dos níveis de tensão do sistema elétrico, característica conhecida como Low Voltage Ride Through (LVRT). Dessa maneira, este trabalho acadêmico apresenta um estudo da capacidade do LVRT durante curtos-circuitos simétrico e assimétricos, usando MATLAB/Simulink®. Além disso, propõe um modelo de divisor de tensão para separar as componentes de queda de tensão positiva e negativa com resultados de simulação do desempenho do gerador durante os distúrbios. Por fim, apresenta uma revisão bibliográfica de diversas soluções em hardware para o aprimoramento da capacidade LVRT, que têm como finalidade proteger os circuitos eletrônicos contra sobrecorrentes e sobretensões, e, em alguns casos, injetar potência reativa na rede.
In the last years, issues related to the environment, especially the use of fossil fuels and the emission of polluting gases into the atmosphere, have gained great international prominence. With the advances of scientific community and the increase of the oil price in the beginning of the 1970s, the use of renewable, non-polluting and clean sources had a great investment by several countries. In this context, wind generation has stood out as one of the most promising, especially due to its economic viability and its fast technological development. Among the different topologies used in wind generation systems, the configuration developed for operation at variable speed is highlighted, which employs the doubly-fed induction generator (DFIG) associated with back-to-back electronic converter to control its operation. The main advantages of using DFIG include its greater efficiency in energy conversion, less mechanical rotor stress, independent control of active and reactive power limited to typical values of 30% of the rated power. On the other hand, it is known that, during the occurrence of a disturbance, such as an electrical fault, the rotor currents can reach high magnitudes in order to damage the rotor side converter. In addition, overvoltages in the DC link capacitor occur due to the loss of power transfer capacity on grid side converter. However, wind turbines may be required to main in operation even during a fault, in addition to contributing the restoration of voltage levels in the electrical system, a feature known as Low Voltage Ride Through (LVRT). In this way, this academic paper presents a study of LVRT capacity during symmetrical and asymmetrical short-circuits, using MATLAB/Simulink®. In addition, it proposes a voltage divider model to separate positive and negative voltage sag components, showing results of simulation of generator’s performance during the disturbances. Finally, it presents a bibliographic review of several hardware solutions to improve LVRT capacity, which aim to protect electronic circuits against overcurrents and overvoltages, plus, in some cases, inject reactive power into the network.
In the last years, issues related to the environment, especially the use of fossil fuels and the emission of polluting gases into the atmosphere, have gained great international prominence. With the advances of scientific community and the increase of the oil price in the beginning of the 1970s, the use of renewable, non-polluting and clean sources had a great investment by several countries. In this context, wind generation has stood out as one of the most promising, especially due to its economic viability and its fast technological development. Among the different topologies used in wind generation systems, the configuration developed for operation at variable speed is highlighted, which employs the doubly-fed induction generator (DFIG) associated with back-to-back electronic converter to control its operation. The main advantages of using DFIG include its greater efficiency in energy conversion, less mechanical rotor stress, independent control of active and reactive power limited to typical values of 30% of the rated power. On the other hand, it is known that, during the occurrence of a disturbance, such as an electrical fault, the rotor currents can reach high magnitudes in order to damage the rotor side converter. In addition, overvoltages in the DC link capacitor occur due to the loss of power transfer capacity on grid side converter. However, wind turbines may be required to main in operation even during a fault, in addition to contributing the restoration of voltage levels in the electrical system, a feature known as Low Voltage Ride Through (LVRT). In this way, this academic paper presents a study of LVRT capacity during symmetrical and asymmetrical short-circuits, using MATLAB/Simulink®. In addition, it proposes a voltage divider model to separate positive and negative voltage sag components, showing results of simulation of generator’s performance during the disturbances. Finally, it presents a bibliographic review of several hardware solutions to improve LVRT capacity, which aim to protect electronic circuits against overcurrents and overvoltages, plus, in some cases, inject reactive power into the network.
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Palavras-chave
Geração eólica, Gerador de indução duplamente alimentado, Afundamento de tensão, Faltas elétricas, Wind generation, Doubly-fed induction generator, Low voltage ride through, Voltage sag, Electrical faults