A new distributed cooperative secondary voltage control in an unbalanced microgrid

Abstract

The negative-sequence reactive power-conductance (Q - -G) droop control strategy is a conventional method to compensate the output unbalance voltages in an islanded MG. Nevertheless, the conflict between unbalanced voltage compensation and negative-sequence reactive power sharing, caused by the impedances mismatching of distribution lines and distributed generators, has not been solved only by Q - -G droop control. In this paper, a distributed cooperative secondary unbalanced voltage control strategy is proposed to decrease the output voltage unbalance factor(VUF) of each droop-controlled DG as well as to further enhance the negative-sequence reactive power sharing effectiveness among DGs by properly shifting up and down the Q - -G droop characteristic of each DG. And an algorithm for adaptive VUF weight coefficient is proposed to better suppress VUF under severe imbalance conditions. Furthermore, a negative-sequence small-signal model of a MG under unbalanced condition, considering the communication delay time of proposed SUVC, is established to analyze the system stability and transient performance under the influence of some critical parameters. Finally, the effectiveness of the proposed strategy is validitied by the simulation results at the real-time emulator of StarSim HIL.