A two-stage PV grid-connected inverter with optimized anti-islanding protection method

Anti-islanding protection of power disturbing method for a two-stage photovoltaic grid-connected inverter is designed in this paper. There is little coupling between the input and output power of the inverter as the dc-dc and dc-ac conversion is independent from each other. Step change of voltage across the dc-link filtering capacitor results in a change of stored energy of the capacitor and consequent a disturbance on the current injected into the grid. This algorithm is adopted for the islanding detection of the inverter. When the grid is gone, the disturbing current results in disturbance of the voltage across the ac terminals, and the islanding protection can be triggered. This method has merit of little non-detection zone for islanding detection.