A battery energy storage system (BESS) for medium voltage direct current (MVDC) or high voltage direct current (HVDC) grids or systems. The BESS comprises split-battery units and an isolated DC-DC converter interface connecting the battery units to the MVDC or HVDC system. The isolated BESS converter is a soft-switched modular multilevel dual-active-bridge (DAB) converter which has DC fault rid-through capability. The converters can be single-phase or poly-phase configurations and can be controlled to maintain a desired DC output under normal and DC grid fault conditions.
