Active Cell Balancing of Series Connected Lithium Ion Battery Cells with Flyback Converter

Lithium-ion battery packs used in electric vehicles often suffer from cell voltage imbalance due to manufacturing inconsistencies, temperature variations and unequal aging characteristics. Cell imbalance reduces the available capacity, decreases battery life and may lead to overcharging or over-discharging of individual cells. Active cell balancing techniques provide an efficient solution by redistributing energy among cells instead of dissipating excess energy as heat. Among various active balancing methods, the flyback converter-based topology has attracted considerable attention because of its galvanic isolation, high efficiency, bidirectional energy transfer capability and modular structure. This paper presents active cell balancing using a flyback converter for lithium-ion battery packs. The operating principle, control strategy, converter design and balancing algorithm are discussed in detail. The proposed balancing system transfers energy from higher-voltage cells to lower-voltage cells through a flyback converter transformer, wherein the energy transfer takes place from cell to the pack. The MATLAB Simulation results are presented and performance evaluation is done on the basis of balancing time and state of charge equalization.