A comparison of different control strategies in inverter connected micro-grids

Inverter connected renewable energy sources are becoming increasingly general in micro-grids. It has brought many problems and challenges to the stability and transient of the system. Traditional constant voltage and constant frequency (CVCF) method fits for many occasions, but it can´t plug and play easily because it needs communication between the micro-grid controller and energy sources. Peer to peer droop-control strategies can just solve this problem. An overview of isolated micro-grid model has been introduced firstly, then the CVCF method and two droop control strategies have been described in detail. All three control strategies are brought to the power system simulation software DigSilent PowerFactory and a comparison of them in terms of transient performance in voltage and frequency control has been made. The simulation results show that the CVCF method performs best in steady state and both two peer to peer droop-control strategies can ensure micro-grid stability in pure inverter connected system. Each strategy has its advantages as well as limitations, which depend on different occasions. Some following-up research prospects are also raised in the end of this paper.