A modular multilevel converter with half-bridge submodules for hybrid energy storage systems integrating battery and UltraCapacitor

In this paper, a modular multilevel converter (MMC) and the control algorithm are proposed for hybrid energy storage systems (HESS) that combine battery and UltraCapacitor (UC). Half bridges integrated with low voltage UC modules are utilized as the submodule of the converter, and the high voltage battery pack is put at dc bus. Compared to traditional HESS topologies and other MMCs for HESS applications, the proposed MMC increases the overall system efficiency, reduces the cost of dc side passive components, and is favorable for grid energy storage systems. The mathematical model of the converter is derived. A control algorithm to independently control the power from battery and UC is proposed. Real-time simulation results are provided to verify the theoretical analysis.