Improved active cell balancing approach based on state of charge for lithium iron phosphate batteries

In this paper, the improved active cell balancing approach based on state of charge (SOC) is proposed to equalize cells in a battery pack, targeting to complete cell equalization in charging process. A battery equivalent circuit model (ECM) is used to represent a battery with experimental verification. Based on the state space equation derived from the battery ECM, a hybrid extended Kalman filter is applied to dynamically estimate cell SOCs with only one additional current sensor required to calculate current of each cell. Simulation results show that the proposed approach can charge more capacity to battery pack than terminal voltage based approaches.