Lifespan Maximization of Modular Battery Energy Storage Systems with State-of-Charge Imbalance Constraints

Modular battery energy storage systems (MBESSs) are a promising technology to mitigate the intermittency of renewables. In practice, the batteries in an MBESS have disparities in their remaining useful life (RUL). Hence, the least healthy battery dictates the MBESS lifespan, which has motivated the development of RUL balancing methods. However, existing methods have not considered maximum lifespan extension, nor the SoC imbalance generated by RUL balancing, which can reduce the MBESS useable capacity. Hence, this article first develops a general optimality criterion for RUL balancing, that holds for any battery whose degradation rate is a strictly convex function of power. Accordingly, an optimal RUL balancing method is proposed to maximize the MBESS lifespan, while limiting the SoC imbalance and adhering to operational constraints through a model predictive control framework. Simulation and experimental results verify the effectiveness of the proposed method.