A Harmonic Injection Method to Reduce Filter Inductance or Capacitance for MMC-BESS

Battery energy storage system based on double-star structure, which is also called modular multilevel converter battery energy storage system (MMC-BESS) is a practical topology to expand the capacity of single machine. However, the inherent current fluctuation in submodule will have a negative influence on batteries. Therefore, the LC passive filter is introduced as the power buffer unit to suppress the battery current fluctuation. First, the components of DC side current in submodules are deduced. Then, the design method of LC passive is proposed. Next, the influence of different current or voltage harmonic injection method on battery current is analyzed. On this basis, a second-order circulating current and third-order harmonic voltage injection method is proposed to decrease the filter inductance or capacitance. Finally, the correctness of proposed method is verified by simulation on MATLAB/Simulink.