Two-degree-of-freedom current regulation of grid-connected inverters in microgrid

Microgrid is an effective way to integrate the distributed energy resources into the utility networks. Conventionally, the voltage-source inverters in microgrid with sinusoidal current regulation are used in grid-connected mode. In this paper, a two-degree-of-freedom nonsinusoidal current regulation (NCR) is proposed for both the distributed power generation and power quality enhancement. The equivalent Thevenin-Norton circuit is provided to clarify the concept that NCR with virtual admittance leads to the power quality improvement. It is demonstrated that without any harmonic current sensor or additional compensating device, the harmonics of the voltages at the point of common coupling and currents in microgrid can be mitigated significantly. Time-domain performance evaluation results confirm the concept.