Improved Active Frequency Drift Islanding Detection Method for Grid-Tied Distributed Energy Resources

Anti-islanding protection/detection (AIP) is required for the grid connected distributed energy resources (DERs) due to the concern of personnel and equipment safety. Passive AIP and communication-based AIP methods are not desirable in DERs because of larger Non-Detective Zone (NDZ) for the former and expensive communication infrastructure for the later, respectively. Active AIP method, such as active frequency drift (AFD) was reported for DERs owing to its simple design and smaller NDZ. However, AFD method affects quality of the DER output current due to the AFD current injection. The performance of the AFD injection is determined by NDZ and total harmonic distortion (THD) of the output current. This paper proposes two AFD current injections, (i) combined sine and rectangular injection, and (ii) combined sine and trapezoidal injection. The former proposed AFD current injection generates 25% less THD compared to the conventional AFD injection, and the latter one generates 39% less THD. The reduction in THD at the proposed current injections can increase reactive power injection and result in less NDZ and quicker island detection. The effectiveness of the proposed AFD current injection waveforms is theoretically analyzed and verified through time domain simulation results.