Topology and control strategy of compact centralized MMC-BESS

In order to solve the problems of large device cost, large DC output ripple and high-frequency switching of sub-modules of flexible half-bridge cascade DC direct-mounted energy storage device, this paper proposes a compact centralized modular multilevel converter battery energy storage systems (CMMC-BESS) topology. It utilizes a half-wave alternating MMC (HA-MMC) as the grid-side power conversion systems (PCS) to reduce submodule (SM) capacitor requirements and a hybrid cascaded energy storage unit on the DC side. This structure improves power density and output waveform quality compared to conventional centralized MMC-BESS. A dedicated DC-side control strategy is proposed, which greatly reduce DC bus voltage fluctuations. Furthermore, a state of charge (SOC) balancing strategy is introduced, which solves the problem of SOC balancing of batteries at different levels of the system. MATLAB/Simulink simulations verify the feasibility of the proposed topology and the effectiveness of the control strategies under dynamic power reversal conditions and SOC imbalance scenarios.