Rule-based health-aware power sharing for a multi-unit battery energy storage system

A multi-unit battery energy storage system (BESS) which aggregates individual battery units can be used to provide auxiliary services in power grid. Existing state-of-charge (SOC)-based power sharing strategies for multi-unit BESSs rarely consider the unit-level battery aging characteristics and may lead to high aging rates. This paper proposes a rule-based health-aware power sharing strategy to cope with the above challenge. An aging function considering impacts of initial SOCs and charge–discharge power is used in the proposed strategy to calculate the aging rates of battery units. According to the characteristics of aging function, multi-unit BESSs are classified into three types. Three operation rules based on type parameters and initial SOCs are designed to reduce the aging rate of the whole multi-unit BESS. Rule-based power sharing algorithms and corresponding parameter conversion approaches are developed to implement the operation rules. One-hour and 24-hour testing cases based on BESSs with different aging characteristics are carried out to validate the effectiveness of the proposed strategy. Simulation results show that, compared to the existing SOC-based power sharing strategies, the proposed strategy is able to reduce the overall aging rate of the whole multi-unit BESS. It is also shown that the advantages of the proposed strategy are more prominent when the regulation flexibility of BESS is higher or the aging function is more nonlinear.