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

In a seaport microgrid (SMG), power sharing among distributed generation (DG) units is hindered by power coupling, line changes, and frequent power fluctuations caused by ship charging and discharging through cold ironing, which, in turn, threatens system stability and inverter security. This article 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. First, 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. Second, 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. Third, 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.

I. Introduction

As an important hub for marine transportation, the port is being gradually developed into the most important logistics information center in the world. Meanwhile, it is also a major energy consumer and polluter in the surrounding area due to the energy-intensive processes, logistics, and industries. Air pollutants from ships, port freight vehicles, and port equipment include particulate matter, sulfur dioxide, and nitrogen oxides, and the shipping sector contributes up to 2.2% of total global emissions [1]. With the clean and inexhaustible nature of renewable energy, the seaport microgrid (SMG) with cold ironing based on distributed generation (DG) is a promising solution for the full electrification of ports in the future. It can also provide redundancy for port power systems as a backup of the main grid [2]. In terms of system security and seaport demands, SMGs have also nonnegligible issues concerning device safety and power quality in them.