An Enhanced Instantaneous Circulating Current Control for Reactive power and Harmonic Load Sharing in Islanded Microgrids

To address inaccurate load demand sharing problems among parallel inverter-interfaced voltage-controlled distributed generation (DG) units in islanded microgrids with different DG power ratings and mismatched feeder impedances, an enhanced voltage control scheme based on actively compensation of circulating voltage drops is proposed in this paper. Using proposed strategy, reactive power and harmonic currents sharing are shared accurately and proportionally without knowledge of feeder impedances. As the proposed local controller consists of two well-separated fundamental and harmonic voltage control branches, the reactive power and harmonic currents can be independently shared without having remarkable effects on the amplitude and quality of the DGs voltage, even if nonlinear (harmonic) loads are directly connected at the output terminal of units. In addition, the accurate load sharing can also be attained when the plug-and-play performance of DGs and various loading conditions are applied to the system. The effects of communication failures and latency on the performance of proposed strategy are also explored. Design process of the proposed control system is presented in detail and comprehensive simulation studies on a three-phase microgrid are provided to validate the effectiveness of the proposed control method.