Variable-Gain State-of-Charge Balancing Method for Smart Battery Packs

This paper investigates state-of-charge (SOC) balancing in battery energy storage systems (BESS) using integrated dc-dc converters, which commonly referred to as smart batteries. Mathematical models are developed for both conventional fixed-gain and proposed variable-gain balancing strategies. In the variable-gain method, the control gain is adapted in real-time based on the instantaneous SOC deviation, enabling faster convergence without compromising dc-link voltage stability. Analytical results demonstrate that the theoretical variable-gain approach achieves balancing up to five times faster than the fixed-gain method. The models are validated through simulations and Controller Hardware-in-the-Loop (C-HIL) experiments. The proposed strategy requires only a firmware update, making it suitable for retrofitting existing systems and applicable across different battery chemistries, including second-life applications.