Abstract
In grid energy storage system based on batteries, the interface converter topology plays a significant role in the optimized operation of the system. Among the different types of converters, the split battery type modular multilevel converter (SBMMC) has become a promising technology for interfacing the storage system with a medium voltage grid which can also perform battery management. This paper proposes a droop based control for state of charge (SoC) balancing among the battery modules (BMs) in SBMMC for a grid-connected battery energy storage system (BESS). First, steady-state analysis of the SBMMC is performed which forms the basis for SoC balancing scheme. Consequently, the droop based control is applied to balance SoC among the arms and sub-modules (SM) by controlling appropriate reference voltages. For SoC balancing among the three phases of the upper and lower arms, zero sequence voltage (ZSV) is injected to the respective reference voltages of each arm. The proposed SoC balancing method has been validated through relevant simulation results.