Distributed Power Sharing Control Based on Adaptive Virtual Impedance in Seaport Microgrids With Cold Ironing

Abstract

In a seaport microgrid (SMG), power sharing among distributed generation (DG) units is hindered by power coupling, line changes as well as frequent power fluctuations caused by ship charging and discharging through cold ironing, which in turn threatens system stability and inverter security. This paper proposes a delay-tolerant distributed adaptive virtual impedance control strategy for assigned active and reactive power sharing, so as to suppress the circulating current among DGs. Firstly, the nonlinear impedance-power droop equations (IPDEs) are derived to actively update the resistive and inductive components of virtual impedance, which can accommodate changes in line structure and output power. Secondly, by means of low-bandwidth communication with quantized data and time delay, the desired power terms derived from practical consensus protocols are fed into the IPDEs, for which the proposed scheme gives a quantitative maximum tolerable communication delay with respect to power sharing accuracy. Thirdly, considering the voltage drop caused by virtual impedance, inspired by traditional synchronous generators, we design a virtual impedance loop based on virtual damping and inertia to preserve voltage dynamics. Finally, an SMG containing four DG units is simulated to verify the effectiveness of the proposed strategy on both active and reactive power sharing.