An Islanding Detection Method Based on the Reactive Power Disturbance for Multiple Inverter-Based DG Systems

In this article, an islanding detection method for multiple inverter-based distributed generation systems is proposed, which is based on perturbing reactive power output. An asymmetric form of positive and negative reactive power disturbance (RPD) is presented so that there always exists a certain total amount of disturbance in the system. To decrease the disturbance amplitude without expanding the nondetection zone (NDZ), a positive feedback of frequency difference is added to the disturbance. A RPD synchronization method without communication among inverters is proposed so that the averaging effect caused by unsynchronized reactive disturbances can be eliminated and the island can be detected in a multiple distributed generator (DG) system. In addition, the islanding detection criterion is improved by establishing the relationship between the direction of disturbance and the numerical symbol of frequency difference, so there is no misjudgment of islanding detection in a weak grid. Finally, an experimental platform consisting of three 6kW three-phase grid-connected inverters and a 99.9 kVA islanding detection test device is established. The experimental and simulation results indicate that the proposed method performs fast and precise islanding detection for the multiple-DG system with small NDZ and little impact on power quality. Additionally, no misjudgment happens in a weak grid.