A capacity-based equalization method for aged lithium-ion batteries in electric vehicles

Abstract

A capacity-based equalization method for active balancing is proposed to increase the usable capacity of aged lithium-ion batteries within a minimum of balancing effort. The main goal of the presented algorithm is to predict the equalization charge for each cell, which is needed to fully charge and discharge every cell of the battery in the next cycle. For this, State-Of-Charge (SOC) and State-Of-Health (SOH) of each cell must be determined. The predicted energy is balanced at the beginning of the cycle and further balancing is performed only if the parameters of the cells change. This ensures that the minimum possible balancing effort is achieved. To validate the performance of the proposed method, a simulation is carried out. For this purpose, a battery model and Battery Management System (BMS) model are built in Matlab/Simulink. The parameters of the simulated cells differ in capacity and initial SOC to imitate an aged battery. The simulation results verify that the developed balancing method can improve the usage of aged batteries compared to conventional methods. This algorithm for active balancing can be used in second life cases of battery systems.