State-of-charge estimation based on microcontroller-implemented sigma-point Kalman filter in a modular cell balancing system for Lithium-Ion battery packs

Cell balancing in large battery packs requires accurate state of charge (SOC) estimation for individual cells. This paper presents a low complexity sigma-point Kalman filter to estimate the state-of-charge (SOC) of Lithium-Ion battery cells. The proposed sigma-point Kalman filter is of 1^st order, and can be easily implemented on a simple microcontroller around a dc-dc converter in a modular cell balancing system. The approach is verified experimentally on a battery pack containing twenty-one balancing converters and twenty-one 25 Ah Lithium-Ion cells under high-current (up to 100A) cycling.