Virtual inductor-based islanding detection method for grid-connected power inverter of distributed power generation system

An islanding detection method is proposed for a distributed power generation system that comprises a DC power source and a grid-connected power inverter connected in parallel to the utility. Besides serving to generate the fundamental real power, the grid-connected power inverter also acts as a virtual inductor when the frequency is slightly higher than the fundamental voltage frequency of the utility. The distributed power generation system is the only source supplying power to the load when the utility is interrupted; consequently, the amplitude or frequency of the load voltage changes because of the operation of the virtual inductor. Hence, the proposed method can immediately detect the islanding operation. A prototype was developed and tested to demonstrate the performance of the proposed islanding detection method. Experimental results show that the proposed method can detect islanding operations effectively.