Effect of Unbalanced Cells in Lithium-ion Battery Pack Performance and SOC Estimation

This paper mainly focuses on the effect of cell unbalancing on the overall performance of a battery pack, as well as the challenges associated with designing a protection system for the Battery Management System (BMS). With the increasing trend towards fully electric aircraft, cars, buses, bikes, etc., the battery pack has become the sole power source for these vehicles. Consequently, it's imperative for the battery pack to possess high efficiency and a robust protection system. To enhance efficiency, the battery pack must be fully utilized, meaning that the maximum amount of charge stored in it should be used for useful work. This can only be achieved when all cells in the battery pack are charged and discharged at the same rate, ensuring homogeneous heat dissipation. Cell balancing mechanisms are employed to achieve this balance, ensuring all cells have the same charge/discharge rate. The paper discusses various scenarios, including balanced, unbalanced, worse, and practical methods of balancing conditions. The results demonstrate how balancing impacts pack performance and helps in estimating the battery pack's State of Charge (SOC).