Review of Impedance-Reshaping-Based Power Sharing Strategies in Islanded AC Microgrids

In islanded AC microgrids, loads are supplied by parallel inverters-based distributed generation (DG) units. Accurate power sharing, which is always degraded by the mismatched line impedances of DG units, is an essential mission. Reshaping the output impedance of DG units is an effective method to improve power sharing performance via eliminating the impedance mismatch. This paper classifies and summarizes various impedance-reshaping-based power sharing strategies. Firstly, the comprehensive evaluation criteria of the power sharing methods are illustrated in terms of power sharing accuracy, unbalanced and harmonic power sharing, influence on voltage regulation, dependence on communication and feasibility in practical applications. According to the operating principles, the existing impedance reshaping methods are categorized into four groups: fixed virtual impedance, adaptive virtual impedance regulation, impedance droops, and reconfiguration of inner loops. Then the advantages and disadvantages of the four groups of impedance reshaping techniques are discussed respectively. Finally, the characteristics of different impedance-reshaping-based power sharing methods are summed up and future research trends of impedance reshaping strategies for power sharing improvement in islanded AC microgrids are predicted.