Prioritizing Battery Management System Functionalities for Risk Mitigation

This paper provides the results of a study undertaken to better understand the Battery Management System (BMS) architectures and develop a minimum set of BMS safety functionalities to minimize the loss exposure in large energy storage systems (ESSs). A scenario-based FMEA (failure modes and effects analysis) was utilized in this study. Various failure scenarios were evaluated based on functions to be performed by the BMS. The failure scenario propagation is described in stages. Each stage could have multiple BMS functions (operational and safety) active. As the failure initiates and propagates, the scenario progresses to the next stage, eventually resulting in the outcome. The criticality of each BMS safety function was calculated by ranking the function based on the stage in which it was activated in each scenario. The ranking process was repeated for all scenarios and the overall rank was determined by the sum of ranks across all scenarios. It was found that the BMS function responsible for preparing the system for fire suppression (e.g., close all openings and seal vents) when fire is detected is the most critical. The second most critical function was found to be a complete system trip when a cell is detected to have entered a thermal runaway condition. The other safety functions in order of priority are pack switch fail-to-trip, inverter/charger fail-to-trip and cell temperature isolating trip functions. A distributed architecture has been found to be more suitable for large multi-cell applications like utility based ESSs.