Active Power and SOC Balancing Techniques for Resilient Battery Energy Storage Systems under Asymmetric Grid Voltage Scenarios

Asymmetric grid voltage conditions can result in uneven three phase operation of grid connected power converters. Operation of Modular Multilevel Converter (MMC) having submodules with energy storage elements under such grid conditions can result in unbalanced state of charge (SOC) among battery modules, which is undesirable. In this paper, power balancing strategies for resilient operation of BESS using a double-star chopper cell (DSCC) topology based MMC under asymmetric AC grid voltage scenarios are proposed. This is achieved through power balancing techniques using external output grid current control and control of circulating currents that are internal to the converter. The internal power balancing technique is further extended to obtain per-phase SOC-balancing, without exceeding rated operating power condition, even under adverse grid voltage scenarios.