Battery Management System Design for Lithium-ion Battery Packs
There is an abundance of research dedicated to understanding lithium-ion batteries at the cell-level. However, the cell-level models or estimation algorithms cannot be directly applied to battery modules or packs used in EVs that are composed of tens to hundreds or thousands of cells. Pack or module-level modeling and estimation must take into consideration the temperature distribution, manufacturing-induced parameter (impedance, capacity) variances, pack topology (electrical interconnections), and thermal interactions between cells.
Our lab focuses on developing a novel pack/module-level modeling framework for control and optimization. We have showed, experimentally and mathematically, that the aging dynamics of each cell is influenced by the adjacent cells it is interacting with, both, electrically and thermally. We study the characteristic time-scales and use singular perturbation theory to derive a reduced-order aging model for an interconnected cell that is shown to depend on the thermal gradient in a serially interconnected module.