Zero-sequence network voltage compensation by a three-phase four-wire grid-connected converter

This paper presents a zero-sequence voltage compensation strategy using a grid-connected three-phase four-wire inverter. The main function of the inverter is to interface the distributed generation and the distribution network. However, the inverter can also perform ancillary services such as voltage regulation at the point of common coupling. Initially, current and voltage control loops based on a mathematical modeling are presented to regulate the positive-sequence voltage. Then zero-sequence current and voltage control loops are also presented to compensate the unbalanced voltages. The inverter is then controlled to synthesize currents at its terminals that compensate the zero-sequence voltage and regulate the positive-sequence voltage at its nominal value. Digital simulations are also presented to validate the zero-sequence voltage compensation strategy and the mathematical analysis.