Resolving Kirchhoff’s Laws for Parallel Li-Ion Battery Pack State-Estimators

A state-space model for Li-ion battery packs with parallel-connected cells is introduced. The key feature of the model is an explicit solution to Kirchhoff's laws for parallel-connected packs, which expresses the branch currents directly in terms of the model's states, applied current, and cell resistances. This avoids the need to solve these equations numerically. To illustrate the potential of the proposed model for pack-level control and estimation, a method to bound the error of a state-estimator is introduced and the modeling framework is generalized to a class of electrochemical models. It is hoped that the insight brought by this model formulation will allow the wealth of results developed for series-connected packs to be applied to those with parallel connections.