Optimal energy-dissipation control for SOC based balancing in series connected Lithium-ion battery packs

Abstract

Since the state-of-charge (SOC) based balancing can prolong the battery pack’s life and maximize its capacity, implementing the balancing process in the battery management system (BMS) can explicitly reduce the cost of the battery based energy-storage-system (ESS). With the same initial SOC distribution, different balancing topologies may lead to different amounts of energy transferred in the balancing process due to the energy transferring efficiency of equalizers. Furthermore, the more energy equalizers transfer, the more energy and time balancing process will consume. Thus, instead of solely minimizing the balancing time for balancing optimization, it is critical to take into account the energy dissipation of balancing process. This paper presents a novel balancing optimization method from the perspective of minimizing the energy dissipation of balancing process. First, we introduce a two-step balancing strategy in the fast charging system. This strategy can simplify the modular design of the balancing system, and ensure the safety performance of the fast charging system while maximizing the balancing current. Second, an effective system modeling method is proposed for different balancing topologies. With different initial SOC distributions, we simulate the energy dissipation for different balancing topologies. Simulation results are presented to show that the cascade and cascade-series connection topologies would achieve a balanced state in the optimal energy dissipation.