Performance Evaluation of Modularized Global Equalization System for Lithium-Ion Battery Packs

Abstract

Battery management system has attracted mounting research attention recently, within which cell equalization plays a key role. Although many research and practices have been devoted to developing various structures of cell equalizers, there are still substantial opportunities for performance improvement yet to investigate. In particular, mathematical modeling and systematic analysis of equalizer systems are limited. In this paper, the performance analysis of the modularized global equalizer system for Lithium-ion battery cell equalization is conducted analytically. Specifically, a mathematical model is developed to emulate the equalization dynamics by considering both charging/discharging and energy loss. Analytical formulas are derived to evaluate the performance of the global equalizer. The introduced model is also compared with the state-of-the-art structures in terms of equalization speed and energy loss. Numerical studies show that the modularized global equalization outperforms others by its substantial reduction on energy loss with similar equalization performance and much less equalizers. In addition, a module segmentation guide is provided to facilitate the equalization system design. Lithium-based battery technology offers performance advantages over traditional battery technologies, which makes it promising in application such as automobiles, portable devices, power grid, etc. To ensure the Lithium-ion batteries working efficiently, reliably and safely, battery equalization systems play a critical rule, especially in large volume battery packs. Various equalization structures have been proposed to balance the state of charge within a string of battery cells. In this paper, we first review the state-of-the-art equalization structures in a unified model representation scheme, and then focus on a modularized global equalization structure with much less equalizers. Based on the mathematical models for performance evaluation, the modularized global equalization system outperforms the state-of-the-art structures in terms of energy loss with similar equalization speed. In addition, we provide a module segmentation guide to determine the number of modules in the system design.