Research on SOC Balancing Control Strategy of Direct-hanging Energy Storage System on the DC Side

DC-side cascaded H-bridge direct-hanging energy storage system possesses efficient large-capacity power storage and release technology that can effectively balance the power grid's supply and demand differences and enhance the power system's stability and controllability. State of charge (SOC) balance control is key in this system, as it improves energy storage utilization, extends battery life, and enhances system stability and safety. In a balanced control strategy based on SOC ordering, due to the slow update of SOC data, some sub-modules experience frequent switching during the charging and discharging process, leading to an excessive module switching frequency. This paper investigates the mechanism of excessive module switching frequency and proposes a balanced control strategy based on SOC sorting and rotational switching optimization. This strategy greatly reduces the switching frequency of sub-modules while maintaining the SOC balancing effect intact. Additionally, a simulation model of a ±35kV/140MW DC-side direct-hanging energy storage AC grid-connected system is built in the PSCAD/EMTDC environment for steady-state simulation under various operating conditions to validate the correctness and feasibility of the balanced control strategy based on SOC sorting and rotational switching optimization.