A Voltage Droop-Based State of Charge Control among Split Batteries in Modular Multilevel Converter for Grid Energy Storage Interface

Abstract

In grid energy storage systems based on batteries, the interface converter topology plays a significant role in the optimized operation of the system. Among the different types of transformer-less high-power 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 packs 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 SoCs among the arms and submodules (SM) by controlling the reference voltages. For SoC balancing among the three phases of the upper and lower arms, appropriate zero sequence voltage (ZSV) is injected to the respective reference voltages of each arm. The proposed SoC balancing method has been validated through simulation results.