Battery Charge Equalization-State of the Art and Future Trends 2005-01-3474

High-voltage battery packs which employ large series strings of battery cells can be found in many applications including utility industry, power backup, wheelchairs, electric, and hybrid vehicles. As the battery pack is charged and discharged as a single unit, differences in cell capacities, individual cell temperature, internal chemical characteristics, internal resistance, and degradation can cause capacity imbalances in the form of voltage variations. Imbalanced cell voltages can cause cell overcharging and over-discharging damage, and decrease the total storage capacity and lifetime of the battery pack. While balancing the voltages of the batteries will prevent any problems stemming from capacity mismatch, there are many ways to instantiate the solution. This paper reviews, analyses, and classifies various existing charge equalization techniques including capacitive, inductive, and transformer storage methods.