Parallel control of Three-Phase Four-Leg inverter based on virtual impedance

This letter proposes a sequential control method for three-phase four-leg(3P4L) inverter to improve the output voltage imbalance and power imbalance of parallel system under unbalanced conditions. In order to make the capacity of each inverter in the parallel system match, it is proposed to use the droop control on the first three legs, the negative sequence current and the fourth leg current use the virtual impedance method to control the distribution of positive sequence, negative sequence and zero sequence current respectively, the front three leg and the fourth leg of the 3P4L inverter control independently. Finally, the output voltage is balanced at the same time the output current and the output power of the parallel system are distributed according to the capacity of the parallel inverter under unbalanced conditions, and the circulation of the system is reduced. The correctness of the method is verified by simulation.