基于周期交替电流扰动的孤岛检测方法

对于分布式电源并网系统，当电网断电时可以使用主动频率偏移法检测孤岛效应。但是，若在非检测区内电流扰动角与负载角相匹配，则主动频率偏移法将出现无法识别孤岛效应的问题。针对上述问题，文中提出了一种新颖的基于周期交替电流扰动的孤岛检测方法。在保证扰动电流与公共耦合点电压同步前提下，前一个周期扰动电流频率向上偏移，当前周期扰动电流频率向下偏移。根据公共耦合点电压频率是否周期高低交替变化来识别孤岛现象。经过仿真和实验验证，该方法不但可以准确识别孤岛效应，而且解决了主动频率偏移法存在的非检测区问题。

Islanding Detection Method Based on the Alternate Current Disturbances

The active frequency drift (AFD) method can be used to detect the islanding status for distributed grid-connected power system. However, when the angle of the current disturbance matches with the load angle in the non-detecting zone (NDZ), the AFD method cannot identify the islanding. In order to solve the above problem, a novel islanding detection method based on the alternate current disturbances is proposed. In the case that the disturbed current is in phase with the voltage at the point of common coupling (PCC), the current frequency shifts up in the previous cycle and shifts down in the current cycle. The islanding is detected by judging whether the voltage frequency at the PCC shifts up and down alternately. Simulation and experimental results verify that the proposed method can not only identify the islanding very well, but also solve the NDZ problem of the AFD method.