Multi-layer Cell Balancing using Switched Inductor and Switched Capacitor Topology

In electric vehicles large number of series connected cells are required to get high voltage. During normal charging and discharging operation these cells get imbalanced due to manufacturing tolerances and self-leakage current resulting into reduced voltage and deterioration of cells permanently as some of these might get overcharged or deep discharged. Hence, cell balancing is crucial for performance improvement and extended life of the battery. Balancing time and capacitor current are key parameters to judge the quality of a balancing circuit. In this work, a multi-layer cell balancing scheme has been proposed that provides rapid balancing with reduced charging current of the capacitors. The first layer of the proposed technique is derived from a buck-boost converter topology, where inductor is responsible for balancing of a pack consisting of two cells. The second and third layers of the proposed technique are derived from the double tiered switched capacitor circuit, where capacitors are used to do the equalization between battery packs. Modelling and designing of each layer of the proposed topology has been presented. The proposed topology is simple and versatile for industrial applications. The simulation results confirm that the proposed technique improved balancing speed and reduced switching current.