Controle cooperativo de conversores distribuídos para o aprimoramento da qualidade de energia elétrica em microrredes isoladas
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Data
2022-08-03
Autores
Rodrigues, Diego Tardivo
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Microrredes trifásicas a 4-fios apresentam grandes desafios de operação uma vez que podem se tornar desbalanceadas, com a presença de componentes de sequência negativa e zero na tensão e na corrente. Quando estas microrredes operam de forma isolada, os desequilíbrios bem como a distorções harmônicas produzidas por cargas não lineares e desbalanceadas podem afetar a qualidade da energia e a estabilidade de operação do sistema. Adicionalmente, evitar uma possível sobrecarga de uma unidade geradora, proporcionado pela distribuição de cargas na microrrede bem como diferentes impedâncias de linha entre barramentos, tem sido atualmente um desafio. Logo a presente tese propõe contribuições focadas no compartilhamento de potência ativa, reativa, harmônicos e desequilíbrios em uma microrrede (MR) trifásica a 4-fios quando operada em modo ilhado. Os controladores são desenvolvidos para compartilhar proporcionalmente essas potências entre as unidades de geração distribuída (GD), com base no algoritmo consensus agindo de modo distribuído e utilizando o conceito de impedância virtual. Isto deve evitar sobrecarregar as unidades de GD uma vez que o sistema de controle deve garantir um compartilhamento adequado destas potências entre os GDs da MR. Em primeiro momento o trabalho apresenta uma estratégia para o compartilhamento de potências (ativa, reativa, harmônica e desbalanço) na MR, fazendo uso da CPT (do inglês Conservative Power Theory) no domínio das componentes simétricas generalizadas, bem como do algoritmo consensus para geração de impedâncias virtuais. Com esta técnica foi possível obter o desacoplamento dos efeitos das componentes de sequência negativa e zero no compartilhamento da potência de desbalanço o que é demonstrado por meio de uma análise comparativa com a metodologia encontrada na literatura, a qual faz uso da CPT. Na sequência é proposto um novo sistema de controle com foco no compartilhamento de corrente eficaz por fase ao invés do compartilhamento de potências. Este sistema é baseado também no algoritmo de consensus para equalizar o valor eficaz da corrente entre as fases dos GDs na MR isolada a 4-fios contendo cargas desequilibradas e não-lineares. Para fazer isto é utilizado um controle de droop por fase para regular a magnitude da tensão, e o compartilhamento da corrente harmônica é realizado utilizando o conceito de impedância virtual. Adicionalmente o controle proposto garante regulação de tensão, fazendo com que a MR opere no seu valor nominal de tensão. O algoritmo consensus além de propiciar compartilhamento do valor eficaz da corrente, também proporciona o compartilhamento igualitário do valor eficaz da corrente harmônica entre cada fase de cada GD que compõe a MR, bem como garante que a distorção harmônica da tensão no PAC de cada GD permaneça dentro dos limites definidos pelas normas. Resultados de simulações demonstram o funcionamento e a efetividade da estratégia de controle proposta. Por fim é apresentada uma nova proposta (usando o mesmo cenário do sistema estudado no início do trabalho), para que o compartilhamento das potências (ativa, reativa, harmônica e desbalanço) seja realizada por GD monofásicos e trifásicos da MR. Neste caso o droop foi alterado para regular a tensão por fase, bem como o algoritmo consensus e as impedâncias virtuais que também foram ajustadas por fase. Com isso, foi possível que geradores monofásicos ao serem inseridos na MR trifásica de 4-fios possam também compartilhar suas potências, ajudando na operação da MR.
Three-phase 4-wire microgrids present major operating challenges as they can become unbalanced, with the presence of negative and zero sequence components in voltage and current. When these microgrids operate in islanded mode, unbalances as well as harmonic distortions produced by non-linear and unbalanced loads can affect power quality and system operation stability. Additionally, avoiding a possible overload of a generating unit, provided by the distribution of loads in the microgrid as well as different line impedances between buses, has currently been a challenge. Therefore, the present thesis proposes some new contributions focused on sharing active and reactive power, harmonics and unbalances in a three-phase 4-wire microgrid (MR) operating in islanded mode. The controllers are developed to proportionally share theses powers between the Distributed Generation units (DG), based on the consensus algorithm acting in a distributed way and using the concept of virtual impedance. This should avoid overloading a DG unit since the control system must ensure an adequate sharing of these powers between the DGs units into MR. At first, this thesis presents an improved power sharing strategy (active, reactive, harmonic and unbalance) into the MR, using the Conservative Power Theory (CPT) in the domain of generalized symmetric components, as well as the consensus algorithm for virtual impedances generation. With this proposed technique, it was possible to obtain the decoupling of the effects of the negative and zero sequence components in the sharing of unbalance power, which is demonstrated through a comparative analysis with the methodology found in the literature, which makes use of CPT. Next, a new control system is proposed with a focus on sharing currents instead of powers. This system is also based on the consensus algorithm to equalize the RMS value of the current between the phases of the DGs in the 4-wire isolated MR containing unbalanced and non-linear loads. To do this, a per-phase droop control is used to regulate the voltage magnitude, and the harmonic current sharing is performed using the concept of virtual impedance. Additionally, the proposed control guarantees voltage regulation, making the MR operate at its nominal voltage value. The consensus algorithm, in addition to sharing the RMS value of the current, also provides the equal sharing of the RMS value of the harmonic current between each phase of each DG that makes up the MR, as well as ensuring that the harmonic distortion of the voltage in the PAC of each DG remains within the limits defined by the standards. Simulation results demonstrate the functioning and effectiveness of the proposed control strategy. Finally, a new proposal is presented (using the same scenario of the system studied at the beginning of the work), so that the power sharing (active, reactive, harmonic and unbalance) is performed by single-phase and three-phase DGs of the MR. In this case the droop was changed to regulate the voltage per-phase, as well as the consensus algorithm and the virtual impedances that were also adjusted per-phase. Therefore, it was possible that single-phase generators, when inserted in the three-phase 4-wire MR, can also share their power, helping in the operation of the MR.
Three-phase 4-wire microgrids present major operating challenges as they can become unbalanced, with the presence of negative and zero sequence components in voltage and current. When these microgrids operate in islanded mode, unbalances as well as harmonic distortions produced by non-linear and unbalanced loads can affect power quality and system operation stability. Additionally, avoiding a possible overload of a generating unit, provided by the distribution of loads in the microgrid as well as different line impedances between buses, has currently been a challenge. Therefore, the present thesis proposes some new contributions focused on sharing active and reactive power, harmonics and unbalances in a three-phase 4-wire microgrid (MR) operating in islanded mode. The controllers are developed to proportionally share theses powers between the Distributed Generation units (DG), based on the consensus algorithm acting in a distributed way and using the concept of virtual impedance. This should avoid overloading a DG unit since the control system must ensure an adequate sharing of these powers between the DGs units into MR. At first, this thesis presents an improved power sharing strategy (active, reactive, harmonic and unbalance) into the MR, using the Conservative Power Theory (CPT) in the domain of generalized symmetric components, as well as the consensus algorithm for virtual impedances generation. With this proposed technique, it was possible to obtain the decoupling of the effects of the negative and zero sequence components in the sharing of unbalance power, which is demonstrated through a comparative analysis with the methodology found in the literature, which makes use of CPT. Next, a new control system is proposed with a focus on sharing currents instead of powers. This system is also based on the consensus algorithm to equalize the RMS value of the current between the phases of the DGs in the 4-wire isolated MR containing unbalanced and non-linear loads. To do this, a per-phase droop control is used to regulate the voltage magnitude, and the harmonic current sharing is performed using the concept of virtual impedance. Additionally, the proposed control guarantees voltage regulation, making the MR operate at its nominal voltage value. The consensus algorithm, in addition to sharing the RMS value of the current, also provides the equal sharing of the RMS value of the harmonic current between each phase of each DG that makes up the MR, as well as ensuring that the harmonic distortion of the voltage in the PAC of each DG remains within the limits defined by the standards. Simulation results demonstrate the functioning and effectiveness of the proposed control strategy. Finally, a new proposal is presented (using the same scenario of the system studied at the beginning of the work), so that the power sharing (active, reactive, harmonic and unbalance) is performed by single-phase and three-phase DGs of the MR. In this case the droop was changed to regulate the voltage per-phase, as well as the consensus algorithm and the virtual impedances that were also adjusted per-phase. Therefore, it was possible that single-phase generators, when inserted in the three-phase 4-wire MR, can also share their power, helping in the operation of the MR.
Descrição
Palavras-chave
Componente simétrica generalizada, Algoritmo Consensus, Microrrede, Impedância virtual, Gerador distribuído, Teoria de potência conservativa, Generalized symmetric component, Consensus algorithm, Microgrid, Virtual impedance, Distributed generator, Conservative power theory