The modular multilevel converter based battery energy storage system (MMC-BESS) can effectively mitigate fluctuations in renewable energy generation output

enhancing renewable energy accommodation capacity. This paper proposed a reconfigurable off-grid hierarchical equalization control strategy to address the grid-connected equalization constraints in MMC-BESS. For inter-phase voltage imbalance in the top layer control

the discharge equalization duration was dynamically adjusted by modifying inter-phase equalization weighting coefficients. In the bottom layer control targeting intra-phase voltage differences

a module-level voltage sorting algorithm was introduced to dynamically select cross-phase equalization targets. Through this dual-layer equalization control strategy

voltage equalization among the energy storage units was achieved at both the inter-phase and intra-phase levels

thereby improving the energy utilization rate of the storage system. Active current limiting was incorporated to prevent excessive equalization current

ensuring the safety of off-grid equalization operation. A simulation model was established in Matlab/Simulink

and both simulation results and experimental platform tests demonstrate that the proposed control strategy effectively achieves inter-phase and intra-phase voltage equalization in MMC-BESS.