A charge equalization scheme for battery string with charging current allocation

Abstract

Summary This research proposes a charge equalization scheme based on a flyback converter with the polarity‐inverting folding switches together with a set of selection switches for series‐connected batteries. By the selection switches, the converter can provide an additional charging current to the battery with the lowest loaded voltage. In addition to intervening a low current charging to prolong the discrepant charging, a finalizing individual charging is performed to ensure charge equalization even under extremely unbalanced situation. Thus, all the batteries can be allocated with appropriate electric charge through the proposed charge‐balance strategy to make the voltage of all batteries be even after the charging process. Three sets of experiments with different initial conditions are performed. Experimental results show that the charge imbalance can be effectively reduced after the regular current charging for most practical cases. All batteries can be charged to their full capacities with individual charging, even under extremely unbalanced situation. Eventually, the voltage difference among batteries can be alleviated to about 50 mV.