An improved droop control strategy of three-phase inverter for grid voltage unbalance compensation

In this paper, an improved control strategy for three-phase inverter is proposed, which ensures three-phase output voltage symmetry under unbalanced grid voltage. Firstly, the positive and negative sequence separation module is used to obtain unbalance output voltage and current during the grid faults. By calculating output power of the inverter, an improved P-ƒ, Q-U and Q-G droop control strategy is designed to adjust droop curve real-timely. Then three-phase symmetrical voltage reference could be generated. In order to improve the stability of parallel three-phase inverter system, the virtual impedance is further applied. The simulation results presented verify the feasibility of the improved control scheme. Experimental tests and analysis have been provided in this paper.