Active battery cell equalization using a Flyback converter with current mode control

Due to different charge and discharge rates, temperature gradients and coulomb efficiencies, cells in series-connected battery/ultracapacitor packs may have diverse voltage levels. Therefore, equalization stages are essential to extend its lifetime and reduce significant impacts like overcharged cells. This work presents an active equalization stage based on a Flyback converter with current mode control valid for both series-connected battery and ultracapacitor banks. Unlike most of the methods that can be found in the bibliography, expensive bidirectional power switches are not necessary and recirculation of energy is avoided. With just a mesh of bipolar transistors and optocouplers it is possible to equalize all the cells of the battery/ultracapacitor bank, presenting a low-cost active solution. In addition, a design methodology of the proposed system detailing prominent specifications is included in this work along with simulation and experimental results.