Voltage magnitude and frequency control of three-phase voltage source inverter for seamless transfer

This study presents voltage magnitude and frequency control of a three-phase voltage source inverter for distributed generations to achieve a seamless transfer between grid-tied mode and intentional islanding mode. When the grid is normal, the inverter works in grid-tied mode. On the contrary, when the grid fault occurs, the breaker connecting the inverter to the grid must be turned off and the inverter just supplies the power for local loads. By varying the frequency and the magnitude of the inverter output voltage, an output power control, with which the output active and reactive power can be precisely controlled, is presented. To improve the transient response, a virtual inductor with high-pass filter in synchronous d-q frame is proposed. The effectiveness of the virtual inductor is explained by the frequency response of the inverter. Finally, experimental results are given to verify the effectiveness of the scheme.