Control strategies for DC microgrid energy storage systems under SOC balancing objectives

An improved SOC equalization sag control strategy is proposed to improve the equalization rate of the battery SOC for distributed energy storage subsystems of DC microgrids due to the overcharge or over-discharge problem caused by SOC differences. Firstly, the sag factor of the energy storage device is incorporated into the nested inverse tangent function of the SOC, which is used to improve the control characteristics. Secondly, the design of a variable acceleration factor is provided to achieve the equalization speed regulation when the SOC difference is small. After that, the corresponding voltage equalizer is designed to reduce the fluctuation of bus voltage with reference to the consistency control principle. Finally, a simulation model of the energy storage system and SOC equalization control strategy is built for verification and testing. The results show that the designed control strategy significantly improves the equalization characteristics of the SOC and effectively ensures the power balance and voltage stability in the micro-grid energy storage system with excellent control characteristics.