Comparison of State-of-Charge and State-of-Health Balancing Schemes Through a Smart Battery Model with Online Degradation

This work evaluates the state-of-charge (SOC) and state-of-health (SOH) balancing techniques for energy storage systems with distributed power electronics architecture, i.e., batteries with integrated power converters. Two approaches are compared: a SOC balancing technique described in the literature and a cascaded SOH/SOC balancing technique proposed in this paper. In the proposed technique, the SOH balancing computes a SOC deviation, leading to different degradation rates in each battery of the pack. The techniques are compared through long-term simulations using: average models for the power converters, a battery-equivalent electric circuit, and an online degradation model. Comparative graphs of capacity and SOH are presented to compare the techniques. Based on simulation results, it was noticed that SOC balancing has fast dynamics equalization, but it leaves the SOH unbalanced if different capacity initial conditions are considered. On the other hand, the SOH balancing is responsible for imposing imbalance on SOC until the SOH reaches the balance. The results reveal that the proposed technique can balance SOH and leads to higher reliability when compared with the traditional SOC balancing.