An Islanding Microgrid Power Sharing Approach Using Enhanced Virtual Impedance Control Scheme

TLDR

The study proposes an enhanced virtual impedance control scheme for distributed generation units to improve load sharing in islanding microgrids and reduce controller computational load via resonant band‑pass filtering. The scheme regulates DG equivalent impedance at fundamental and harmonic frequencies using line‑current and PCC‑voltage feed‑forward terms, and employs resonant controllers to avoid extracting harmonic components. Experimental results show that the method compensates feeder‑impedance mismatches, enhances reactive and harmonic power sharing, and reduces PCC harmonic voltages, confirming its feasibility.

Abstract

In order to address the load sharing problem in islanding microgrids, this paper proposes an enhanced distributed generation (DG) unit virtual impedance control approach. The proposed method can realize accurate regulation of DG unit equivalent impedance at both fundamental and selected harmonic frequencies. In contrast to conventional virtual impedance control methods, where only a line current feed-forward term is added to the DG voltage reference, the proposed virtual impedance at fundamental and harmonic frequencies is regulated using DG line current and point of common coupling (PCC) voltage feed-forward terms, respectively. With this modification, the impacts of mismatched physical feeder impedances are compensated. Thus, better reactive and harmonic power sharing can be realized. Additionally, this paper also demonstrates that PCC harmonic voltages can be mitigated by reducing the magnitude of DG unit equivalent harmonic impedance. Finally, in order to alleviate the computing load at DG unit local controller, this paper further exploits the band-pass capability of conventionally resonant controllers. With the implementation of proposed resonant controller, accurate power sharing and PCC harmonic voltage compensation are achieved without using any fundamental and harmonic components extractions. Experimental results from a scaled single-phase microgrid prototype are provided to validate the feasibility of the proposed virtual impedance control approach.