Modular Active Charge Balancing for Scalable Battery Packs

Abstract

High-voltage battery packs consist of series-connected lithium-ion cells and require sophisticated battery management systems (BMSs) to maintain safe operating conditions. Active cell balancing is an important task of a BMS, performed in order to improve the usable capacity of the battery pack by equalizing the charge levels of individual cells. With the emerging trend of distributed BMS topologies, the associated balancing architectures are required to be modular, consisting of homogeneous units that minimize integration efforts. In this paper, we propose a modular active charge balancing architecture along with its control scheme for implementation toward such distributed BMSs. Compared with existing approaches, our proposed architecture provides increased charge transfer capabilities, with reduced hardware and control complexity. We propose a closed-form analytical model of the balancing architecture, which can be used to perform fast system-level simulation studies and design space exploration for analyzing efficient device combinations. A hardware implementation of the proposed balancing architecture is developed and measurements made with it are used to validate each part of our analytical model. Using the validated analytical model, we performed a case study, which shows that our proposed architecture provides a 14.5 % improvement in charge transfer efficiency compared with existing approaches.