When the grid fails, the micro-grid systems can use the active frequency drift (AFD) method to detect the islanding phenomenon. However, if the current disturbance angle equals the load angle, the AFD method fails. As for the problem, this paper discusses a novel current-disturbing method in the positive half voltage period. That is, in the positive half voltage period, disturbing the current frequency, and in the negative half voltage period, keeping current frequency in sync with the voltage frequency. Once the islanding occurs, the frequency of the point of common coupling (PCC) will be changed owing to the change of the output current frequency. The islanding can be identified by judging whether the positive and negative half voltage period changes alternately in the form of the positive and negative signs. The simulation results show that the proposed detection method can not only narrow the range of non-detecting zone (NDZ), but also is effective and practical.%当电网发生故障时,微电网系统可以用主动频率偏移法检测孤岛现象.但若电流扰动角与负载角相等时,此时主动频率偏移法将无法判别孤岛效应.针对上述问题,研究了一种新颖的正半周期电流扰动法,在正半周期给电流频率一个扰动,在负半周期电流频率与电压频率保持同步.—旦孤岛现象出现,输出电流频率的变化将导致公共连接点处电压频率的变化,根据相邻半周期频率之差是否连续正负交替变化来检测孤岛现象,通过仿真验证,该方法减小了主动频率偏移法存在的非检测区,检测快速、有效,对电网电能质量的影响也较小.
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