Automatic SOC Equalization Strategy of Energy Storage Units with DC Microgrid Bus Voltage Support

In this paper, an improved sag control strategy based on automatic SOC equalization is proposed to solve the problems of slow SOC equalization and excessive bus voltage f luctuation amplitude and offset caused by load and PV power variations in a stand-alone DC microgrid. The strategy includes primary and secondary control. Among them, the primary control suppresses the DC microgrid voltage f luctuation through the I and II section control, and the secondary control aims to correct the P-U curve of the energy storage system and the PV system, thus reducing the steady-state bus voltage excursion. The simulation results demonstrate that the proposed control strategy effectively achieves SOC balancing and enhances the immunity of bus voltage. The proposed strategy improves the voltage f luctuation suppression ability by approximately 39.4% and 43.1% under the PV power and load power f luctuation conditions, respectively. Furthermore, the steady-state deviation of the bus voltage, △Udc is only 0.01–0.1 V, ensuring stable operation of the DC microgrid in f luctuating power environments. © 2024, Tech Science Press. All rights reserved.