Anti-islanding Protection Method for Multi-source Distribution Network Impedance Measurement Based on Signal Synchronization Injection

Grid-connected distributed generators(DG) need to be equipped with anti-islanding protection to avoid unplanned islanding due to power grid blackouts. The impedance measurement method has the advantages of low non-detection zone and less prone to maloperation compared with passive anti-islanding protection such as over/under voltage and over/under frequency. However, in multi-DG systems, the existing signal injection strategy and islanding identification criteria cannot cope with the protection failure caused by signal interference between DGs. To this end, an impedance measurement method is proposed, which utilizes external synchronous signals to synchronize the injection of detection signals by each DG. Based on the analysis of the impedance measurement characteristics of the DGs before and after islanding, an impedance angle-based islanding identification scheme is determined and the identification criteria are proposed based on the analysis of line parameters, harmonics, and detection signal frequencies. Finally, the signal injection and the corresponding islanding identification method are presented in conjunction with the DG control strategy. Simulation verification based on RTDS shows that the method can effectively identify the grid disturbance and islanding state, and avoid the refusal and false action problems of over/under voltage and over/under frequency anti-islanding protection.