Optimization of Energy Transfer during Active Balancing of Lithium-Ion Batteries

Abstract

In the recent years, lithium-ion batteries are being used as an energy storage in electric vehicles (EV) and hybrid electric vehicles (HEV) to a greater extent. A battery management system consists of three important parts: balancing, management and protection. Balancing is one of the most important part concerning the battery life. Without the balancing system voltages of individual cell will drift over time.1 This will affect the capacity of the battery pack which will result in the battery system failure. Most applications require that cells be connected in series/parallel to meet the voltage requirements, however this can cause imbalance among the cells. Achieving higher charge efficiency by equalizing the unbalanced cells in the pack is the goal of active balancing systems. This project deals with the time optimization for energy transfer between series connected cells that uses an active balancing topology. There have not been many studies in the literature which deals with optimum switching time for energy transfer between the batteries during active balancing. The proposed charge equalization scheme is designed to reduce the time used to transfer energy from the highest charged cell in the stack to the weakest charged cell in the stack. The performance of the optimized energy transfer between high and weak cell using a dynamic duty cycle adaptation is demonstrated by simulation using MATLAB/Simulink. Reference J. Cao, N. Schofield, and A. Emadi, 3–8 (2008).