Design of a multi-level battery management system for a Cascade H-bridge energy storage system

The cascade H-bridge topology is novel for the battery energy storage system (BESS). A multi-level battery management system (BMS), which contains three subsystems, is introduced. The functions and communication of each subsystem are discussed. An algorithm based on extended Kaiman filter is used for the state-of-charge (SOC) estimation in battery modules. The pack SOC is derived from those of the modules according to the current direction. To keep all cells in a balanced SOC value, a four-level balance control method is proposed. The balance for cells and modules depends on extra circuits, while that for packs and phases are accomplished by the H-bridge converters.