Performance Analysis of a Cell Equalizer based on a Multiple Active Bridge

Cell-to-cell voltage imbalance represents a key issue that limits the usable capacity of a battery pack and increases the risks of possible hazard conditions. Active cell equalization circuits integrated within the architecture of Battery Management Systems (BMSs) strongly contribute in reducing and mitigating the occurrence of imbalance conditions by transferring energy between the most charged cells and the least charged ones. However, the adoption of active equalizers for lithium-ion battery systems is currently limited by incomplete knowledge regarding their actual performances and ranges of operability. In this paper, a cell equalizer based on a Multiple Active Bridge (MAB) converter has been investigated and an experimental prototype has been developed with the aim of quantitatively evaluating its performances considering different imbalance conditions. A Hardware-In-the-Loop approach based on an experimentally-calibrated lithium-ion cell has been implemented in order to correctly compare the performances of the cell equalizer avoiding the impact of thermal gradients and aging conditions among the cells. Experimental results have been carried out and different performance parameters have been defined for the analysis, including the residual voltage imbalance at the end of the equalization process, the energy efficiency and the equalization time.