Re-synchronization of Universal Droop Control Distributed Generation Inverter to the Grid

Abstract

The distributed generation (DG) inverters can operate in an islanded mode and a grid-connected mode. Under grid fault conditions, the inverter is disconnected from the main grid and operates in the islanded mode. When DG inverters operate in the islanded mode, they often form a microgrid. The phase and magnitude of the microgrid voltage deviate from the main grid. If the microgrid is connected to the main grid under such condition, it results in a transient overcurrent during the reconnection of the microgrid to the main grid. In order to overcome this problem, this paper presents a new re-synchronization method for universal droop control (UDC) DG inverter. Simulation and experimental results are provided to verify the effectiveness of the proposed method. The result shows that the transient overcurrent can be avoided when a UDC DG inverter-based microgrid connects with the main ac grid.