A Modularized Two-Stage Active Cell Balancing Circuit for Series Connected Li-Ion Battery Packs

This paper addresses a modularized two-stage active cell balancing topology based on an improved buck-boost converter for a series connected Lithium-ion battery string. The proposed topology has a modular structure, each module consisting of three cells, two inductors, and four MOSFET switches. This technique provides module-to-module balancing in the first stage. Moreover, it can simultaneously target and balance two cells in a module in the second stage. Thus, significantly reduces the cell balancing time and increases the system performance with minimal components. The proposed topology has been theoretically analyzed and experimentally verified with a laboratory prototype. The proposed modularization technique is verified experimentally with two modules tested together in a battery string.