Study on Immunity of Distributed Generation System linked to Power System for Voltage Sags

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Distributed generations (DS) connected to power system increases a promising countermeasure for the environmental issue, and their inappropriate operation for voltage sags might cause a serious problems for entire power system. The aim of this study is to investigate the immunity of photo voltaic power generation system (PV-system) that shares largest part of DSs in Japan, for voltage sags. Small magnetic contactors and a scaled PV-system including inverter are prepared and plenty of experimental studies were carried out for electro-magnetic contactors and the inverter linked to power system, following proposed study plan. Results are:1. The open of contactor is affected by the phase angle of the system voltage at the starting time of the sag, the contactor open time after the occurrence of sag varies 10ms to 65ms in this study. The reason of the deviation of the contactor open time is clarified as the deviation of the magnetic excitation current during the voltage sag caused by the deviation of the voltage phase angle at the starting time of the sag. A phenomenon that contactor open time caused by partial voltage sag is shorter than that of complete voltage sag case has been found.2. PV-system Inverter might stop its operation 16ms after the starting time of the sag as the shortest case. The reason of the stop is not the maloperation of the control system, but the protection scheme recommended in the guideline issued by the Ministry of Economy, Trade and Industry (METI), to prevent the stand-alone operation of the PV-system during blackout to avoid the unexpected energization of distribution lines. The solution for this problem by revising the protection scheme has been studied.The results acquired by this study are worth for improvement of immunity of DSs for voltage sags, and effective for the maximum utilization of renewable energy.