Controller design for three-phase inverter with power unbalanced loads applied in microgrids

In this paper, a control scheme for three-phase inverter applied in microgrids is presented, which ensures the three-phase output voltages balanced under power unbalanced loads. Based on the analysis of the output impedance, a proportional-resonant controller is utilized in the inner current-loop to reduce negative-sequence impedance of the inverter. Thus, the controller compensates the voltage distortions caused by 2ω disturbances under power unbalanced loads in synchronous reference frame. Furthermore, by implementing the virtual impedance with a notch filter in microgrids, a trade-off performance between the unbalanced power sharing and the output voltage quality is achieved very well. The effectiveness of the proposed control scheme has been validated by a prototype consisting of two-40-kVA parallel-connected three-phase inverter system.