Adaptive notch filter for synchronization and islanding detection using negative-sequence impedance measurement

Dispersed generation (DG) has been found promising for satisfying the requirements of high power quality in distributed systems. One operation situation, namely, an island, is formed when one or more DG systems and an aggregate of local loads are disconnected from the main grid and remain operational as an islanded entity. Islanding is either due to intentional events, e.g. maintenance outage, or due to unintentional events, such as faults, and their subsequent switching actions. Islanding is usually undesirable because of the potential harm it causes to the existing equipment, human safety, power reliability and quality, etc. Accordingly, anti-islanding schemes are used to immediately detach a DG system from the feeder after islanding. This paper presents an active method of detecting islanding for DG systems by injecting a small negative voltage into the point of common coupling, and then measuring the negative system impedance. In this study, an adaptive notch filter is introduced as a synchronous part instead of a phase-locked loop and as a signal processing unit as well. The proposed control strategy allows DG systems to detect properly the occurrence of islanding in a balanced distribution system. Simulation results show the overall system performance including synchronization, power control, and islanding detection capability of the simulated DG system.