Battery energy storage system (BESS) can dampen power fluctuations from renewable energy sources

while the modular multilevel converter (MMC) facilitates the large-scale integration of batteries. However

MMC submodule (SM) capacitors must suppress power fluctuations at the fundamental and doubled frequencies

which necessitates a large capacitance. In this paper

it is calculated that the capacitance required for MMC-based BESS can be up to 1.7 times greater than that of traditional MMC. Additionally

the volume and weight of SM capacitors in traditional MMC systems account for over 50% of the total system

highlighting the challenge of excessive capacitance in MMC-based BESS. In order to significantly reduce the capacitance value in MMC-based BESS

this paper proposes a compact MMC-based BESS and the corresponding low-frequency power elimination (LFPE) strategy based on a bi-directional three-port converter. By transferring low-frequency power to the common bus and thereby canceling it out

the MMC SM capacitance can be reduced by 99% without increasing the bus capacitance. The effectiveness and feasibility of the proposed system and LFPE control in significantly reducing capacitance values is verified through experiments.