Battery energy storage system modeling : investigation of intrinsic cell-to-cell variations

Cell-to-cell variations can drastically affect the performance and the reliability of battery packs. This study provides a model-based systematic analysis of the impact of intrinsic cell-to-cell variations induced by differences in initial state of charge, state of health, capacity ration, resistance and rate capability. The impact of these cell-to-cell variations was evaluated on the performance of battery packs of different topologies, from series to parallel, and chemistries. For each chemistry and topology, simulations were performed with different levels for each type of intrinsic variation as well as all variations together in order to investigate the combined effects. The most salient changes were observed for cells connected in series. The calculated incremental capacity response for the pack and the single cells was used to select different features of interest that changed depending on the type of variation. From this methodology, the automatic quantification of the variations was attempted at the pack and single cell level. Cell-to-cell variations make each battery pack unique; their quantitation is essential for accurate monitoring