A generalized equivalent circuit model for large-scale battery packs with cell-to-cell variation

Abstract

A critical issue in large-scale battery pack is the capability of assessing the impact of cell-to-cell variation on the pack/module performance. The inhomogeneity of cell parameters is mainly due to manufacturing tolerances, cell degradation, and temperature gradients, and leads to unbalanced current and voltage distribution in the pack. In this paper, a generalized equivalent circuit model is proposed that effectively allows estimating the current and voltage differences between cells/strings in a pack as function of the system architecture and parameters. The model is based on a simplified equivalent circuit model that separates the healthy cells from the ones affected by parameters variation. The proposed methodology has been applied to several pack configurations, typically used for automotive and aerospace applications, and demonstrates high benefits for large scale systems due to the reduced computational effort. The proposed model can be used during the design of the battery pack for estimating the impact of degradation and thermal unbalance in a pack. Look-up-tables can be carried out to describe the behavior of battery pack at steady-state conditions and can be used by the Battery Management System (BMS) for on-line estimation of the operating conditions of the cells.