Novel voltage equalisation circuit of the lithium battery pack based on bidirectional flyback converter

Abstract

Lithium batteries have become the main power source for new energy vehicles due to their high energy density and low self-discharge rate. In actual use of series battery packs, due to battery internal resistance, self-discharge rate and other factors, inconsistencies between the individual cells inevitably exist. Such inconsistencies will reduce the energy utilisation rate and service life of the battery pack, and even endanger its battery system safety. To improve the inconsistency of series battery packs, this study innovatively proposes an equalisation method based on a flyback converter. The residual power of a single cell is used as an index of inconsistency. A simple and reliable flyback converter is used to achieve balanced energy in the entire group, which make the energy is transferred between any batteries. Compared with the traditional equalisation topology, the equalisation topology proposed in this study reduces the number of components and reduces the volume of the equalisation system. Moreover, the primary side of the energy transfer only needs a set of control signals, which reduces the control difficulty. A series of equalisation experiments were performed using 12 series of battery cells. The results show the effectiveness of the proposed new equalisation method.