Islanding detection method based on second-order harmonic injection for voltage-controlled inverter

The synchronization between DG and microgird is required in order to prevent high inrush current. This high inrush current may trigger the protection or danger the facility in the system. On the other hand, anti-islanding inverters shall always detect islanding condition when they connect to microgrid. It is required that disconnecting from microgrid in two seconds whenever islanding occurred. General speaking, there are two method to detect islanding-passive and active method. This paper developed a voltage-controlled inverter which could connect to microgrid with synchronization and detect islanding condition actively. According to second harmonic voltage injection method, the proposed inverter detects the second harmonic current to decide whether islanding is happened.