This paper suggests a fast and robust dq voltage control strategy for a three-phase four-leg voltage source inverter (VSI) operating with highly unbalanced loads in a stand-alone distribution network. The main objective is to balance the output voltages of the four-leg inverter under unbalanced load conditions with fast transient response. The proposed control strategy consists of a proportional-integral (PI) voltage controller and a proportional current loop in each phase. The voltage controller and the current control loop are, respectively, used to regulate the instantaneous output voltage and generate the pulse width modulation (PWM) voltage command with fast transient response. A voltage decoupling feedforward path is also used to improve the system robustness. Simulation results are also carried out using the DIgSILENT PowerFactory software to verify the effectiveness of the suggested control strategy.
