Systematic comparison of modular multilevel converter topologies for battery energy storage systems based on split batteries

The advent of the modular multilevel converter has spawned a new breed of battery energy storage systems, able to connect directly to the medium voltage grid without a mains transformer. This paper compares the three most prominent variants: The single-delta bridge-cell (SDBC), the single-star bridge-cell (SSBC) and the double-star chopper-cell (DSCC). The comparison is based on a pareto optimal design approach, respecting the trade-off between power conversion efficiency and size of the passive components, which present important driving factors of the overall system costs. To make the assessment fair, the total semiconductor die area is equalized among all candidates and the switching frequency is controlled such that the average switched power is equal for all three converters.