Propagação de harmônicas produzidas por inversores fotovoltaicos e transformadores assimetricamente magnetizados na geração distribuída
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Data
2018-12-07
Autores
Fortes, Rárison Roberto Acácio
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Universidade Estadual Paulista (Unesp)
Resumo
As profundas mudanças que os sistemas de distribuição de energia elétrica vêm experimentando, devido à crescente penetração de unidades de Geração Distribuída (GD), têm resultado, inevitavelmente, na efetiva ruptura da forma tradicional de controlar e operar o sistema elétrico. A conexão em larga escala de unidades de GD impõe às distribuidoras de energia uma série de desafios técnicos, econômicos e regulatórios, necessários para preservar a continuidade e o nível de Qualidade da Energia Elétrica (QEE) na rede. Além dos benefícios que justificam o investimento, os sistemas de GD contribuem com alguns impactos negativos para o sistema elétrico, entre eles, destacam-se aqui a geração de harmônicas e a injeção de corrente contínua (CC) na rede, em regime permanente, e seus efeitos sobre os transformadores de potência. O incremento de uma componente de fluxo CC em seu enrolamento secundário altera o ponto de operação natural e eficiente do transformador, trazendo prejuízo não só à sua vida útil, mas também à sua funcionalidade na rede. Esta condição favorece a geração e propagação de harmônicas adicionais no sistema alimentador, afetando negativamente o sistema elétrico, sendo esta análise uma contribuição original deste trabalho. Neste sentido, considera-se com grande relevância o estudo de comportamento dos equipamentos projetados para operar essencialmente com sinais em corrente alternada (CA) e que passam a ser submetidos, simultaneamente, a excitações com corrente contínua. Com o objetivo de analisar não apenas o efeito, mas também a causa da dupla excitação, esta tese procura elucidar o princípio de funcionamento e as deficiências do inversor de Geração Distribuída Fotovoltaica (GDFV) como dispositivo responsável pela conversão estática da potência elétrica CC, fornecida pelo gerador fotovoltaico, em potência elétrica CA. A estrutura seguida neste trabalho procura descrever os fundamentos físicos que cercam o fenômeno da dupla excitação em transformadores de potência, utilizando o modelo matemático representativo para análise em regime permanente, identificando a reação e os impactos destes equipamentos no sistema elétrico. Os impactos técnicos devem ser previstos e analisados, sobretudo em redes de distribuição, para garantir os padrões mínimos de QEE no ponto de consumo e evitar o comprometimento das cargas alimentadas. Neste contexto, são investigados os aspectos relativos à propagação das diferentes componentes harmônicas nas redes de distribuição, bem como suas principais consequências, sobretudo com respeito a possíveis ressonâncias harmônicas entre os componentes naturais das redes e os dispositivos de compensação de reativos.
The deep changes that electric power distribution systems have been experiencing due to the increasing number of Distributed Generation (GD) units, have inevitably resulted in the effective rupture of the traditional way of controlling and operating the electrical system. The large-scale connection of GD units imposes on energy utilities many technical, economic and regulatory challenges necessary to preserve the continuity and the Electric Power Quality (EPQ) level on the grid. In addition to the benefits that justify the investment, GD systems have some negative impacts to the electrical system, among them, the harmonic generation and Direct Current (DC) injection on the grid, and its effects in the power transformers. The increase of a DC flow component in the secondary winding changes the standard and efficient operational point of the transformer, causing damage not only to its lifespan but also to its functionality on the grid. This condition favors the additional harmonics generation and propagation in the feeder system, adversely affecting the electrical system, being this analysis an original contribution of this work. In this way of thinking, it is considered with great relevance the study of the equipment behavior designed to operate essentially with signals in alternating current (AC) and simultaneously subjected to excitations with direct current (DC). Whereas the objective of analyzing not only the effect but also the cause of the double excitation, this thesis seeks to elucidate the operating principle and the deficiencies of the Photovoltaic Distributed Generation (PVDG) inverter as a device responsible for the static conversion of DC electric power, provided by the photovoltaic generator, in AC electric power. The structure presented in this project intents to describe the physical foundations surrounding the double excitation phenomenon in power transformers, using the representative mathematical model for permanent analysis, identifying the reaction and the impacts of these equipment in the electrical system. The technical impacts must be predicted and analyzed, especially in electric power distribution, to guarantee the minimum standards of EPQ at the consumption point and to avoid any damage to the powered loads. In this context, the aspects related to the different harmonic components propagation in the distribution networks, as well as their main consequences are investigated, especially regarding the possible harmonic resonances between the standard components of the grid and the reactive compensation devices.
The deep changes that electric power distribution systems have been experiencing due to the increasing number of Distributed Generation (GD) units, have inevitably resulted in the effective rupture of the traditional way of controlling and operating the electrical system. The large-scale connection of GD units imposes on energy utilities many technical, economic and regulatory challenges necessary to preserve the continuity and the Electric Power Quality (EPQ) level on the grid. In addition to the benefits that justify the investment, GD systems have some negative impacts to the electrical system, among them, the harmonic generation and Direct Current (DC) injection on the grid, and its effects in the power transformers. The increase of a DC flow component in the secondary winding changes the standard and efficient operational point of the transformer, causing damage not only to its lifespan but also to its functionality on the grid. This condition favors the additional harmonics generation and propagation in the feeder system, adversely affecting the electrical system, being this analysis an original contribution of this work. In this way of thinking, it is considered with great relevance the study of the equipment behavior designed to operate essentially with signals in alternating current (AC) and simultaneously subjected to excitations with direct current (DC). Whereas the objective of analyzing not only the effect but also the cause of the double excitation, this thesis seeks to elucidate the operating principle and the deficiencies of the Photovoltaic Distributed Generation (PVDG) inverter as a device responsible for the static conversion of DC electric power, provided by the photovoltaic generator, in AC electric power. The structure presented in this project intents to describe the physical foundations surrounding the double excitation phenomenon in power transformers, using the representative mathematical model for permanent analysis, identifying the reaction and the impacts of these equipment in the electrical system. The technical impacts must be predicted and analyzed, especially in electric power distribution, to guarantee the minimum standards of EPQ at the consumption point and to avoid any damage to the powered loads. In this context, the aspects related to the different harmonic components propagation in the distribution networks, as well as their main consequences are investigated, especially regarding the possible harmonic resonances between the standard components of the grid and the reactive compensation devices.
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Palavras-chave
Distorções harmônicas, Geração distribuída, Qualidade da energia elétrica, Sistemas fotovoltaicos, Transformadores de potência, Saturação assimétrica, Harmonic distortion, Distributed generation, Power quality, Photovoltaic systems, Power transformers, Asymmetric saturation