Comparison Between Battery Cell Level Dynamics and Pack Level Dynamics Using Equivalent Circuit Models

Large battery systems include parallel-connected cells and modules, and these can exhibit complex and unexpected behaviours. In this paper, we investigate parallel-connected battery equivalent circuit models and show that cell inhomogeneity leads to differences between parallel groups that are not typically accounted for in battery management system (BMS) models. The theoretical analysis is complemented by experimental results using impedance data to parameterise models from individual cells, and from a pack assembled from the individual cells. We show that cell-level parameterisation is sufficient for parameterising a pack model-but only if parasitic impedances and inhomogeneity between cells is well understood.