A Voltage-Independent Islanding Detection Method and Low-Voltage Ride Through of a Two-Stage PV Inverter

This paper presents an islanding detection method for a two-stage photovoltaic (PV) inverter. The novelty in this method is that it does not rely on instantaneous value of the grid voltage for identifying the islanded condition. Instead, the islanding condition is detected by the saturation of the proportional integral (PI) controller of the outer voltage control loop. This makes the proposed detection algorithm more reliable compared with other voltage-based detection algorithms, as it is immune to malfunctions caused by the sudden load changes or other transients. In addition, a simple but accurate implementation strategy for low-voltage ride through (LVRT) operation is also proposed and integrated with the anti-islanding operation. Both these methods are placed inside the overall control structure that can perform seamless transition between grid-connected and standalone modes of operation. The simulation results demonstrate the effectiveness of the proposed anti-islanding and LVRT techniques. Finally, hardware results on a 2 KW laboratory prototype are presented for experimental verification of the proposed anti-islanding and LVRT schemes.