Evaluating the Generality and Effectiveness of Equivalent Circuit Models for Battery Strings With Heterogeneous Cells Connected in Parallel

The equivalent circuit model (ECM) is widely used in lithium-ion battery management systems because of its well-balanced simplicity and accuracy. However, it remains unclear whether the ECM can accurately model the dynamics of parallel-connected battery cells when the individual cells are heterogeneous. To address this issue, an approximate-parameter ECM (AECM) has been proposed to represent the input–output characteristics of parallel batteries with inconsistent capacity and internal resistance in the frequency domain. Additionally, a first-order ECM for parallel individual cells has been established for comparison. The transfer functions of the two models are calculated to analyze how model errors change with increasing inconsistencies among cells in parameters such as individual cell capacity and internal resistance. Finally, electrochemical impedance spectroscopy is used to validate the errors of the AECM under different operating conditions. Theoretical analysis and experimental results indicate that even with a 6% capacity variation in a battery pack with heterogeneous cells connected in parallel, the AECM can still accurately characterize the battery pack dynamics with an error of less than 2% under various conditions, including several representative operation profiles for batteries in electric vehicle and power system applications, demonstrating the broad effectiveness of the proposed AECM.