Control design of grid-connected three-phase inverters for voltage unbalance correction

The increasing presence of single-phase distributed generators and unbalanced loads in the electric power system may lead to unbalance of the three-phase voltages, resulting in increased losses and heating effects. A type of voltage unbalance with a high probability in (low voltage) distribution networks is the unequal voltage magnitudes at the fundamental system frequency (under- and over-voltages). To decrease this voltage unbalance problem three-phase four-wire inverter-connected distribution units can be used. This paper proposes a control method for a three-phase four-wire inverter for Distributed Generation (DG) units which has a resistive behaviour for disturbances. The effect of the proposed control method on the voltage unbalance in the distribution network is simulated and is compared to the classical sinusoidal control strategy. The simulation results show the positive effect of the proposed control strategy on voltage unbalance.