This study presents a comparative performance analysis involving single-and double-stage photovoltaic (PV) systems, which are connected to a three-phase four-wire electrical system by means of a four-leg inverter topology. The doublestage PV system is composed of a step-up DC/DC converter and a four-leg grid-connected inverter, while in the single-stage PV system the PV array is directly connected to the inverter DC bus. In addition to the active power injection into the grid, both PV systems have two attractive features, described as follows: (i) power quality improvement due to their capability to perform active power-line conditioning, such as load harmonic current suppression, reactive power compensation, and load unbalance compensation; (ii) dynamic improvement in the occurrence of abrupt solar irradiation variations, which is achieved through the implementation of a feed-forward control loop (FFCL) acting directly in the inverter DC-bus voltage control loop, resulting in speeding up of the dynamics of both the DC-bus voltage and the injected grid-inverter currents. The referred comparative analysis addresses the static and dynamic performances considering the PV systems operating under the action of the FFCL, as well as performing active power-line conditioning. Simulation and experimental results are presented to evaluate and validate the proposed study.
Resumo -Este trabalho apresenta um sistema fotovoltaico (FV) trifásico de duplo estágio de conversão de energia conectado à rede elétrica, o qual é capaz de lidar com problemas de sombreamentos parciais em arranjos FV. Condições de sombreamentos parciais podem afetar o desempenho de sistemas FV, uma vez que as técnicas tradicionais de seguimento do ponto de máxima potência (MPPT -Maximum Power Point Tracking) podem operar em pontos de máximos locais de potência ao invés de máximos globais. Sendo assim, são apresentas quatro técnicas de MPPT bioinspiradas no método de otimização dos lobos cinzentos (GWO -Grey Wolf Optimization), as quais são capazes de extrair o ponto de máximo global de potência do sistema. Tais técnicas são denominadas neste trabalho como GWO, GWO-Beta, GWO-IC (Incremental Conductance) e GWO-P&O (Perturb and Observe). As referidas técnicas são avaliadas e comparadas uma com as outras empregando um sistema FV composto por um conversor CC/CC Boost e um inversor trifásico a três braços. Por meio de resultados de simulação e experimentais o desempenho e eficácia das quatro técnicas de MPPT são avaliadas levando em consideração o tempo de convergência, as oscilações de potência em regime permanente, assim como a eficiência na busca do ponto de máxima potência. 1 Palavras-Chave -Otimização dos Lobos Cinzentos, Sistema Fotovoltaico, Sombreamento Parcial, Técnicas de Seguimento do Ponto de Máxima Potência. Abstract -This paper presents a double-stage threephase grid-tied photovoltaic (PV) system capable to deal with partial shading condition issues in PV arrays. Partial shading conditions can affect the overall performance of PV system, once traditional techniques employed to perform the maximum power point tracking (MPPT) can operate in local maximum power pointsArtigo submetido em 14/05/2018. Primeira revisão em 13/07/2018. Aceito para publicação em 08/02/2019 por recomendação do Editor Marcello Mezaroba. http://dx.(LMPP) instead global maximum power point (GMPP). Therefore, four MPPT techniques based on the grey wolf optimization (GWO) are presented, which are able to track the GMPP. Such techniques are denominated in this paper as GWO, GWO-Beta, GWO-IC (Incremental Conductance) and, GWO-P&O Perturb and Observe). The referred MPPT techniques are evaluated and compared to each other employing a PV system composed of a step-up DC/DC converter and a three-leg three-phase inverter. By means of simulation and experimental results, the performance and effectiveness of the MPPT techniques are evaluated considering the convergence time, the power oscillations in steady-state, as well as the maximum power point tracking efficiency.
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