Offline Equalization Control of Modular Multilevel Converter-Based Battery Energy Storage System
R. He, Kai Ge Tian, Zhibin Ling
Abstract
The modular multilevel converter-based battery energy storage system (MMC-BESS) can help the power grid to run safely and stably, which plays an important role in the modern power grid. The inconsistency of cells in BESS may lead to overcharge or overdischarge of cells, which may decrease the operation life of battery packs and cause safety problems. Normally, before the MMC-BESS is connected to the grid, it is necessary to prebalance the system batteries in an offline state. This article analyzes the topology, the mathematical model, and the equalization control model in offline MMC-BESS. According to the analysis, an offline MMC-BESS stepwise balancing control strategy considering the state of charge, state of health, and state of function, is proposed. In this strategy, the state of dischargeable energy is set as the criterion of offline equalization of the system. The balancing of submodules in MMC-BESS would be achieved by controlling the circulating currents and voltages of arms. Finally, the feasibility of the offline equalization control strategy is verified by simulation and experiment.