Distributed control strategy for voltage and frequency restoration and accurate reactive power-sharing for islanded microgrid

Abstract

For a conventional droop-controlled islanded microgrid, the poor reactive power-sharing and drop of bus voltage and frequency caused by line impedance mismatch and droop characteristics are inevitable. So far, consensus-based distributed control algorithms, in which a secondary control layer with the integration of voltage and frequency restoration and reactive power-sharing compensation mechanisms, has been treated as a promising solution. However, for most of the currently available distributed algorithms, it is the active power-sharing rather than the reactive power-sharing that was made the control goal, which is opposite to the fact that accurate power-sharing could always hold considering the integration effect in the active power control loop. Although a few recently published distributed algorithms added the reactive power-sharing goal in the second control layer, the system efficiency and reliability may deteriorate because a large circulating current could be induced at the malfunction of the communication network since there is no virtual impedance injected at the bottom control layer to limit that. This paper proposes a voltage and frequency restoration method based on the dynamic average consensus algorithm and an accurate reactive power-sharing method based on a first-order consensus algorithm and virtual impedance method. A simple pseudo-unidirectional communication network with a narrow communication band is adopted for the proposed distributed control to lower the communication burden and system complexity. The operational principle is first analyzed in detail. The proposed strategy is easily implementable and features not breaking droop characteristics. Then simulations and hardware-in-the-loop (HIL) real-time experiments verify the proposed approach.