Microgrid power quality enhancement using a three-phase four-wire grid-interfacing compensator

This work presents a three-phase four-wire grid-interfacing power quality compensator for micro-grid applications. The compensator is proposed for use with each individual distributed generation (DG) system in the micro-grid, and consists of two four-phase-leg inverters (a shunt and a series), optimally controlled to achieve an enhancement of both the quality of power within the micro-grid and the quality of currents flowing between the micro-grid and utility system. Using four-phase-leg inverters, the compensator can compensate for all the unwanted positive-, negative- and zero-sequence voltage/current components found within an unbalanced utility grid. Specifically, the shunt four-leg inverter is controlled to ensure balanced voltages within the micro-grid and to regulate power sharing among the parallel-connected DG systems. The series inverter is controlled complementarily to inject negative-and zero-sequence voltages in series to balance the line currents, whilst generating zero real and reactive power. The proposed system has been tested in simulations and experimentally using a laboratory hardware prototype.