Automatic phase-shift method for islanding detection of grid-connected photovoltaic inverters

The traditional frequency-shift methods for islanding detection of grid-connected PV inverters-the active frequency drift method and the slip-mode frequency-shift method-become ineffective under certain paralleled RLC loads. The automatic phase-shift method is proposed in this paper to alleviate this problem. The method is based on the phase shift of the sinusoidal inverter output current. When the utility malfunctions, the phase-shift algorithm keeps the frequency of the inverter terminal voltage deviating until the protection circuit is triggered. Simulation and experiments are performed for verification.