Distributed Sequential Balance Control for Modular Multilevel Converter-Based Battery Energy Storage System

With the integration of distributed battery energy storage systems into submodules, the MMC-BESS provides an effective large-scale energy storage solution to medium/high-voltage AC/DC hybrid power grids. Different from centralized battery energy storage systems implemented in microgrids, the MMC-BESS circuit comprises three phases with six bridge arms, each bridge arm is built from multiple submodules (SMs). Such an MMC-BESS can be viewed as a three-layer energy system: the inter-phase, inter-bridge arm, and inter-submodule layers. This paper develops a distributed balancing strategy for the threelayer MMC-BESS, where the control inputs of each SM depend solely on its local states and adjacent SMs. The finite-time boundedness concept is applied to quantitatively determine the convergence time of single-layer energy storage systems. The control input is designed sequentially from the inter-submodule to the inter-phase. Finally, the effectiveness of the proposed balancing approach is validated through numerical simulations.