A Decentralized Impedance Reshaping Strategy for Balanced, Unbalanced and Harmonic Power Sharing in Islanded Resistive Microgrids

In an islanded microgrid, the wire impedance mismatches among distributed generation (DG) units lead to inaccurate power sharing results, which influences the system's normal operation. The output impedances of DG units can be reshaped to deal with this issue. In this paper, a virtual impedance regulation strategy for the resistive microgrid is proposed based on the combination of droop control and adaptive virtual impedance regulation (AVIR). Firstly, DG units operate in droop mode and the steady-state reactive power from Q-f droop is restored as the reference. Then the droop loops are removed and an AVIR based on the error between instantaneous reactive power and its reference is implemented. Since reactive power sharing with Q-f is relatively accurate, the impedance mismatches could be eliminated by the virtual impedances introduced with the proposed strategy, all the accurate active, reactive, unbalanced and harmonic power sharing could be achieved simultaneously. In this strategy, communication among DG units or between DG unit and central control is not required, neither the wire impedances nor bus voltage or load current is measured, which reveals the high system reliability. Finally, the simulation and experimental results are presented to verify the effectiveness of the proposed control method.