New Conditions and Controllers for State-of-Charge Balancing in Battery Energy Storage Systems

We investigate the state-of-charge (SoC) balancing control problem for a battery energy storage system, which consists of multiple battery units. These battery units are allowed to have heterogeneous battery parameters and are connected in parallel to deliver a desired total power. Existing power allocating controllers have been developed to achieve SoC balancing without taking balancing speed into consideration. Motivated by this observation, we aim to design new power allocating controllers such that accelerated SoC balancing is achieved. To facilitate our control design, we first introduce a new concept, the powered SoC, and establish new sufficient conditions that guarantee SoC balancing among battery units in the discharging and the charging modes. Based on these new sufficient conditions, we design a power allocating controller for each battery unit. It is shown that the proposed power allocating controllers achieve accelerated SoC balancing while delivering the desired total power. One key merit of our control method lies in achieving faster SoC balancing by tuning the power in the powered SoC. Moreover, we provide in-depth discussions on the SoC evolution trends among the battery units, the limiting case, and the parameter choice. Simulation results are given to validate our analytical results.