An active islanding detection method for grid-connected converters

Islanding, detection is a mandatory function for gird-connected converters. The popular slip mode frequency shift and auto phase shift active islanding detection methods are investigated and an improved slip mode frequency shift (IM-SMS) strategy is proposed in this paper. In the proposed method, additional phase shift is introduced to help stimulating the islanding detection function and the algorithm is simplified as well. When the utility grid is disconnected, the algorithm keeps the frequency of the converter output voltage deviating until the frequency protection relay is triggered. The working principle of the method is introduced and the guidance of parameters selection is also provided. The islanding detection performance is evaluated through theoretical analysis, digital simulation and experiment. The IM-SMS method exhibits features of simplicity, easy implementation and high reliability and is expected to be an effective active islanding method.