A fast and energy-efficient nonnegative least square-based optimal active battery balancing control strategy for electric vehicle applications

Abstract

In an electric vehicle, a battery pack with many series-connected cells suffers from charge imbalances caused by manufacturing and varying operating conditions. The battery balancing system overcomes the cell imbalance while providing the required capacity maximization, prolonging the battery life, and safe operation. Various balancing topologies and control algorithms have been developed based on the difference in energy transfer methods. Among these, the passive balancing method is to convert the energy of the highly charged cell into heat. The active balancing method transfers the excessive energy of the high-charged cell to the low-charged cell through an electronic circuit. This type of balancing has high conversion efficiency compared to passive balancing and provides a noticeable improvement in increasing the useable capacity of the battery pack, thus increasing the range of the EVs. In this study, an optimal balancing control strategy for the active cell-to-pack balancing system has been developed. A unidirectional common flyback as a DC-DC converter has been used as a balancing circuit for transferring the excessive energy of the cells to the battery pack. The proposed optimal control algorithm eliminates the imbalances among battery packs in the minimum balancing time that ensures maximizing energy efficiency.