A novel configuration for integration of battery energy storage system into MMC

Modular Multilevel Converter (MMC) with integrated Battery Energy Storage System (BESS) has attracted amount of interest in recent years. However, compared with the common MMC, the SM capacitor voltage fluctuation in MMC-BESS become worse because of the integration of batteries, requiring larger SM capacitor to ensure the operation. This paper analyzes the influence of the integration of battery units on capacitor voltage ripples. Then a novel configuration for integration of BESS into MMC is presented. By using an isolated three-port converter as the battery interface converter, this configuration allows the batteries to connect both upper and lower arms and alleviates the SM voltage ripples problem. After that, the corresponding control strategy is presented. The simulation and experiment results are given to validate the effectiveness of the proposed configuration and control strategy.