Modelling and control of four-wire voltage source inverter under unbalanced voltage condition for hybrid power system applications

In this paper, the operation of three-phase, four-wire voltage source inverter (VSI) under unbalanced voltage conditions is investigated. The inverter is particularly interesting for the simultaneous supply of three-phase and single-phase loads in transformerless hybrid power system (HPS) application. A control strategy for the VSI based on the decomposition of the supply voltages and currents into instantaneous positive, negative and homopolar sequence components is described. The three sequences are controlled using two different rotating reference frame systems, so that the disturbance of the output voltage due to the load unbalances is eliminated. Simulation results are presented to verify the validity of the control strategy.