A micro-grid smooth transfer control strategy based on a special slave distributed generation unit

This paper proposes a novel control strategy for a micro-grid to achieve a smooth transition between grid-connected (GC) mode and stand-alone (SA) mode with the help of a special slave distributed generation (DG) unit. In the conventional smooth transfer control methods, only the control strategy of master DG unit is emphasized; and the slave DG unit outputs constant active and reactive power based on PQ control, which is useless for the smooth transition. In the proposed control strategy, the master DG units adopt the traditional hybrid voltage and current control method. When a utility outage occurs, one special slave DG unit is used to compensate the power mismatch between the output power of DG units and the power consumed by the load, which can suppress the drift of load voltage. When the grid returns to a normal state, the pre-synchronization can be achieved by regulating the output power of this special slave DG unit. The simulation results are provided to verify the effectiveness of this control strategy.