A discrete-time observer for parallel connected battery packs with nonlinear descriptor system dynamics

An observer is developed for the nonlinear descriptor system dynamics of parallel connected lithium-ion battery packs. The observer estimates the states of the individual cells in the pack with stability and existence guarantees provided through linear matrix inequalities. When evaluated on the urban dynamometer driving schedule, the proposed observer performed well, with root mean squared errors (RMSEs) of 0.0072 and 0.0054 in the state-of-charges as well as 0.3A and 0.28A in the currents for cells 1 and 2, respectively. The results also demonstrated the value of incorporating contact resistances in the model. In particular, with the inclusion of a contact resistance of 0.02Ω, the mismatch in currents grew by 9.69% for cell 1 and by 8.55% for cell 2. These results highlight the potential of implementing cell-level state estimation and control in large battery packs accounting for cell-to-cell variability and contact resistances.