Consensus Virtual Output Impedance Control Based on the Novel Droop Equivalent Impedance Concept for a Multi-Bus Radial Microgrid

Most of the existing reactive power sharing schemes that assume parallel architecture are known to be less effective for multi-bus radial microgrids. This article proposes an improved reactive power sharing scheme that exploits the novel concept of droop equivalent impedance into designing a consensus virtual-output-impedance-based droop control scheme. The control scheme leads to two notable improvements: (a) it proves that only either virtual resistance or virtual reactance is sufficient to restore proportional reactive power sharing; (b) only a global coupling gain needs to be tuned and no proportional-integral controller is required. A systematic guideline that establishes the approximate range of stable coupling gain is developed. This simplifies the tuning process of the coupling gain. The power correction performance, the resulting bus voltage behavior, consensus control stability, and the robustness to time delay have been investigated in conjunction with an islanded microgrid modified from the IEEE 34 Node Test Feeder. It is shown that the consensus control scheme is capable to demonstrate accurate power sharing regardless of the changes in the network topology, network impedances, loading conditions, and communication delay.