Effective Coordinated Virtual Impedance Control for Accurate Power Sharing in Islanded Microgrid

In a practical islanded microgrid system, the mismatched line impedance causes serious problems, such as inaccurate power sharing and circulating current. In order to overcome these issues, this article proposes a coordinated virtual impedance control strategy for distributed generation (DGs) units. In the proposed control strategy, both virtual resistance and virtual inductance are simultaneously tuned to compensate the mismatched line impedance among DGs, and the microgrid system stability is enhanced by increasing damping for the whole system. Also, the virtual impedance is adaptively regulated in order to guarantee a good power-sharing performance even if the communication is interrupted or the load changes suddenly. The controller design process and theoretical analysis of the whole system are presented in detail based on small-signal analysis. The feasibility and effectiveness of the proposed control strategy were validated by simulations and experiments with a 1.3-kVA prototype microgrid composed of three DGs.