Análise de ressonância em sistemas de potência com parques eólicos baseados em GIDA

Orientador: Walmir de Freitas FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O incremento da penetracao de parques eolicos (PE) baseados em geradores de inducao duplamente alimentados (GIDA) no sistema de potencia eletrica pode trazer problemas de qualidade de energia relacionados com ressonancia de alta frequencia no intervalo de 180 Hz e 1500 Hz. Dois problemas potenciais sao analisados: Ressonancia instavel pela carateristica de amortecimento negativo dos conversores tipo fonte de tensao (VSC); e ressonancias mal amortecidas pela excitacao de componentes de distorcao de tensao na rede proximos a 5...., 7...., 11.... e 13.... harmonicas. Estas ressonancias sao estudadas com numerosas simulacoes de transitorios eletromagneticos (TEM) ja que levam em conta as carateristicas dinamicas do circuito mas com alto nivel de detalhe e custo computacional. Este documento apresenta o desenvolvimento de metodos simplificados para estudar as ressonancias. Inicialmente, esta dissertacao confirma que em frequencias entre 180 Hz e 1500 Hz, o GIDA pode-se modelar como uma impedancia linear com o modelo average dos VSCs. Posteriormente, desenvolve-se um grafico para identificar rapidamente se um parque eolico vira instavel. Este grafico estabelece uma regiao de risco: se as caracteristicas do parque eolico e da rede (relacao de curto circuito e relacao de potencia compensacao reativa) estao localizadas dentro desta regiao, o parque pode virar instavel. Este problema pode-se mitigar com uma escolha adequada de parametros de controle, e por tanto, nao deveria representar um problema geral para o operador de rede. Mesmo assim, a ressonancia mal amortecida pode ocorrer e deve-se considerar ao operar e projetar PEs baseados em GIDA. Dois graficos adicionais sao propostos para analisar o risco de ressonancias mal amortecidas no sistema. Os graficos estabelecem a regiao de risco correlacionando o nivel de curto-circuito da rede no ponto de acoplamento comum, com a capacidade nominal do parque eolico e o nivel de compensacao de potencia reativa. Dois parametros delimitam a regiao: A frequencia de ressonancia, e a amplificacao de tensao com respeito a distorcoes harmonicas na rede. Os tres graficos propostos nesta dissertacao podem-se obter analiticamente com os modelos de impedancia dos PEs sem necessidade de simulacao. Um metodo baseado em medicao tambem foi desenvolvido para obter os graficos sem conhecimento previo das caracteristicas do parque. Estes metodos para obter os graficos foram validados com simulacoes detalhadas de transitorios eletromagneticos. Os graficos propostos podem serfacilmente obtidos e consultados por engenheiros, e apresentam grande potencial para facilitar a analise de ressonancia em sistemas com PEsAbstract: The increase of the penetration of wind parks (WP) based on doubly-fed induction generators (DFIG) in electric power systems may bring problems associated with high-frequency resonances in the range between 180 Hz and 1500 Hz. There are two main phenomena to be analyzed: unstable resonances, when a resonance occurs in frequencies where the DFIG voltage source converters (VSC) have negative damping characteristic; and weakly damped resonances close to frequencies such as 5th, 7th, 11th and 13th harmonics, which are typically present as background grid distortions. Traditionally, these resonances are studied with electromagnetic transient (EMT) simulations as they are able to account for all dynamic characteristics of the circuit. However, numerous EMT simulations are generally required in the studies, which leads to high computational costs. This dissertation develops simplified approaches to address these resonances. Prior to developing these methods, it is first confirmed that, at frequencies between 180 Hz and 1500 Hz, the DFIG can be modeled as a linear impedance using the average model of the VSCs. Then, a chart is developed to quickly identify if a WP can become unstable. This chart establishes a risk region: if WP and grid characteristics (short-circuit level to wind park size ratio and reactive compensation to wind park size ratio) lay inside this region, the WP can become unstable. It is found that this risk region can be significantly reduced by properly designing the control parameters of the converters. Therefore, high-frequency instabilities are unlikely to become a general concern for utilities. Nevertheless, weakly damped harmonic resonances can still occur and must be considered when operating and designing DFIG-based WPs. Two additional charts are proposed to analyze the risk of weakly damped harmonic resonances in the system. The charts establish a risk region by correlating the short-circuit level of the grid at the point of common coupling, with the WP rated power capacity and reactive power compensation level. Two parameters delimit this risk region: Resonance frequency and voltage amplification with respect to background harmonic distortions in the grid. All three charts proposed in this dissertation can be obtained analytically, based on wind park impedance models, without the need for running any simulation. A measurement-based method is also developed to obtain these charts without prior knowledge of any wind park characteristic. These methods for obtaining the charts were properly validated with detailed EMT simulations. The proposed charts can be easily obtained and consulted by engineers, and have the potential to greatly facilitate resonance assessment in systems with WPsMestradoEnergia EletricaMestre em Engenharia Elétric

Impedance modeling of DFIG-wind turbine system

IEEE International Symposium on Circuits and Systems, ISCAS 2015, 24-27 May 2015The DFIG-wind turbine, can create the potential instability to the existent power grid, equivalently presenting itself as a random voltage source with its dynamic impedance, which has the implicit and varying electrical characteristics with the changeable rotor speed. Thus, it inevitably leads to the mutual interaction between DFIG-wind turbines themselves and dynamic custom loads. This paper studies the closed-form impedance analysis of a practical DFIG-wind turbine system. A small-signal model of the DFIG system in the dq-frame is developed with respect to discrete rotor speeds using the impedance-based approach. Moreover, a practical testing method is adopted to facilitate the verification of the impedance modeling.Department of Electronic and Information EngineeringRefereed conference pape