A Hybrid Islanding Detection Method for One Cycle Controlled PV Inverter System

Abstract

Features like phase locked loop free implementation, simple-structure, grid voltage sensor-less operation, and its feedback response make one cycle control (OCC) inverters suitable and cost-effective for small single-phase photovoltaic distributed generator units. The feedback nature of OCC makes passive islanding detection more effective in comparison with other control methods. A novel hybrid islanding detection method (IDM), which is suitable for OCC inverters, is proposed in this article. The hybridization is done in two levels and is aimed at reducing the nondetection zone of the existing feedback-based passive IDM. The passive first level defense, which is always present, is due to the feedback nature of OCC. When islanding is suspected, the active second level defense is initiated by injecting a short real power disturbance. This accelerates the feedback action and helps in timely detection of islanding. Unlike other active methods, the disturbance is injected only when an islanding condition is suspected. The induced disturbance in real power is momentary, and the inverter goes back to the normal operation under nonislanded conditions. Simulation and experimental studies are performed to verify the effectiveness of the proposed IDM.