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

分布式电源接入电力系统为解决环境问题提供了一种很有前景的对策，但其对电压暂降的不当运行可能会给整个电力系统带来严重的问题。本研究的目的是研究光伏发电系统(光伏发电系统)对电压暂降的免疫力。光伏发电系统在日本的DSS中占有最大的份额。根据提出的研究方案，研制了小型磁力接触器和包括逆变器在内的规模化光伏系统，并对电磁接触器和并网逆变器进行了大量的实验研究。研究结果表明：1.接触器的分闸受暂降启动时系统电压相角的影响，暂降发生后接触器的分闸时间为10ms~65ms。指出接触器分闸时间偏差的原因是由于电压凹陷启动时的电压相角偏差而引起的电压凹陷期间励磁电流的偏差。发现了部分电压凹陷引起的接触器断开时间比完全电压凹陷情况下的短的现象。在最短的情况下，光伏系统逆变器可能会在暂降开始时间16ms后停止运行。停止的原因不是控制系统的误操作，而是经济产业省(METI)发布的指导意见中建议的保护方案，以防止光伏系统在停电期间独立运行，以避免配电线路意外上电。研究了通过修改保护方案来解决这一问题的方法，研究结果对提高DSS对电压暂降的抗扰性，最大限度地利用可再生能源具有一定的参考价值。

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.