对多机并联下应用频移式孤岛检测法面临问题的探讨

针对目前广泛应用的频移式孤岛检测方法——简称频移法，指出当只有部分逆变器采用该方法时，其扰动能力可能不足以撼动孤岛的频率并使其超限，从而提出采用频移法的逆变器比例和频移法正反馈增益的调节等2个问题。针对采用频移法的逆变器比例问题，在最不利情况下进行分析，获得了该比例与逆变器最大过载倍数之间的关系，发现逆变器过载能力越大，采用频移法的逆变器比例可越小；关于频移法正反馈增益的调节问题，本文推导出了正反馈增益与采用频移法逆变器比例的关系，表明正反馈增益必须根据采用频移法的逆变器的比例同步增大。仿真结果验证了上述结论。

Discussion on two issues of frequency shift islanding detection methods in multi-DG operation

For frequency shift islanding detection method (simply referred to as frequency shift method), a very common active method, it is pointed out that if only parts of inverters employ this method, their disturbance strength may be unable to cause the frequency to exceed the limit. And then two related issues are raised: the rate of the inverters employing frequency shift method and the adjustment of positive feedback gain of frequency shift method. For the rate of the inverters employing frequency shift method, in the most unfavorable case, a relationship between it and the maximum overload factor of an inverter is achieved. The relationship shows that this rate can be smaller if the overload capability of inverters are larger. For the adjustment of positive feedback gain of frequency shift method, a relationship between it and the rate of the inverters employing frequency shift method is obtained. This relationship shows that the positive feedback gain should increase according to the rate of the inverters employing frequency shift method. Simulations are performed and verify the previous conclusions.