A new passive islanding detection method for grid-connected PV inverters

In this paper a new passive islanding detection method for grid-connected photovoltaic (PV) inverters is presented. It is based on the system identification theory and the detection algorithm is simple to implement. The islanding detection algorithm is based on simulation of the entire system (PV array, PV inverter, LCL filter, grid, control system). The proposed method has been implemented and experimental results show that an active power mismatch between the PV system and the local load above 11% is required for successfully detect the islanding operation in a time below 0.504s. Insensitivity to short time disturbances, grid impedance variation and variation of the load have been evaluated. The combination of the proposed method with the over/under voltage and over/under frequency protections produces a combined islanding detection method with interesting performances especially in terms of the global nondetection zone (NDZ) which is smaller than other passive methods; however the small NDZ only allows the partial compliance of the IEEE 929-2000.