Synchronization Issues with Irregular Current Injection Islanding Detection Methods in Multi-DG Operation

The islanding detection methods that detect an island through injecting high/low frequency currents or negative sequence currents are called irregular current injection methods in this paper. A synchronization issue of such methods is raised in multi-DG (Distributed Generation) operation. This issue requires that the same frequency irregular currents injected by DG units should be in phase to avoid cancelling each other out. If this issue is not handled properly, the effect of such methods is uncontrollable. In view of this, an approach to this issue is proposed in this paper. According to this approach, the terminal voltage of a DG unit is taken as a reference to conduct the irregular current injection, and only parts of the irregular currents whose frequencies are an integer multiple of the frequency of the reference voltage are employed. Finally, experiments and simulations verify the effect of the proposed approach.