Development of a globally active balance module with range extension effect
Lithium-ion batteries require an effective battery management system (BMS) to avoid overcharged or overdischarged states resulted from cell imbalance. Nevertheless, most existing BMS methods reduce effective ranges of the battery and might acerbate cell imbalance problem. This study manages cell imbalance problem in both charging and discharging stages based on the same globally active balance module. A two-staged charging and balancing scheme compensates cell inconsistency in the charging stage and evenly charges each cell to full state without overcharging any cell. While discharging, a selective balance method is achieved through an external power source injecting balance current to weakest cell in the series. Balance measures in both charging and discharging stages adopted by the current study aim at extending ranges for the vehicles. The proposed globally active balance module is integrated with a 48 V module BMS and range extension effects are evaluated by experiments with laboratory instruments and field tests on a 96 V prototype electrical vehicle. Test results show the proposed balance method is capable of increasing battery range.
