Abstract: In an islanded DC microgrid, there is a problem of slow state of charge (SOC) equalization between distributed energy storage units (DESUs) with different capacities, and for this reason, a fast SOC equalization strategy for DESUs that takes capacity differences into account is proposed. First, the SOC equalizer constructs the relationship between the droop coefficient and SOC through a power function, and the selection of appropriate equalization adjustment coefficients can realize the adaptive control of the droop coefficient, which accelerates the speed of SOC equalization. Then, with the virtual droop equalizer, the effect of line impedance on the accurate current distribution can be eliminated by simply adjusting the PI controller, which improves the current distribution accuracy. Next, the selection range of control parameters for this strategy is determined by system stability analysis. Finally, a DC microgrid hardware-in-the-loop experimental platform is constructed, and by comparing with the existing literature and analyzing the experimental results under different working conditions, it is confirmed that the proposed control strategy not only improves the speed of SOC equalization, but also realizes the fast recovery of bus voltage.

Key words: DC microgrid, distributed energy storage system, state of charge, voltage drop equalization, voltage compensation