A grid-interfacing power quality compensator for three-phase three-wire microgrid applications

This paper proposes a grid-interfacing power quality compensator for three-phase three-wire microgrid applications with consideration of both the power quality of the microgrid and the quality of currents flowing between the microgrid and utility system. It is proposed that two inverters (a shunt and a series) are used for each distributed generation (DG) system in the microgrid. For each inverter, both positive-and negative-sequence components are controlled to compensate for the effects caused by the unbalanced utility grid voltages. Specifically, the shunt inverter is controlled to ensure balanced voltages within the microgrid and to regulate power dispatches among parallel-connected DG systems, while the series inverter balances the line currents by injecting appropriate voltage components. A current-limiting algorithm is also proposed and integrated within the inverter control schemes to protect the microgrid from large fault currents during utility voltage sags (balanced or unbalanced). The proposed compensator has been tested in simulations and experimentally using a laboratory hardware prototype.