Influence of equalization on LiFePO4 battery inconsistency

Capacity inconsistency among cells is a serious problem in battery energy storage systems. The inconsistency reduces battery pack lifetimes and increases their usage costs. Active balancing is an effective technique for performance equalization between cells. Here, a quantitative analysis method based on an active balancing circuit is developed to explain how battery capacity inconsistency is affected by balancing parameters. Four balancing parameters, namely, charge/discharge current rate, initial capacity difference before balancing, balancing current, and balancing time, have been considered to explain the effects on battery capacity consistency. The results indicate that (1) the inconsistency of batteries can be reduced more effectively for discharging with active balancing at small current rates; (2) for an improved balancing effect, it is necessary to maintain a high ratio () of balancing current to charging/discharging current during the balancing process; thus, a larger balancing current is significant; (3) the value of capacity difference reduction ratio () grows more dramatically in discharging at large initial battery capacity differences; and (4) when the balancing current only marginally changes, following the increase of current rate, the ratio () of balancing time to charging duration decreases and the balancing effect becomes inconspicuous in charging, while increases and the balancing effect reduces in discharging. These influence regulations can help us make and optimize balancing control strategies for LiFePO4 batteries. Copyright (c) 2017 John Wiley & Sons, Ltd.