A Global Modular Equalizer Based on Forward Conversion for Series-Connected Battery Strings

Abstract

The battery equalizer using a multi winding transformer has the advantages of easy isolation and fast balancing, but is very difficult to be applied to a large battery string with large numbers of cells connected in series due to the serious mismatching of multiple windings, the high voltage stress on switches, the additional demagnetizing circuits, bulky size, and high implementation complexity. Therefore, a global modular balancing architecture is proposed based on forward conversion, which integrates cell balancing, module balancing, and demagnetizing functions into one circuit, greatly reducing the volume, cost, energy loss, and implementation complexity. A prototype of the proposed equalizer for eight battery cells was built to validate the balancing performances, and a comparison between the proposed equalizer and existing solutions was presented. Experimental and comparative results show that the proposed topology exhibits a good balancing performance with strong robustness, and the measured peak efficiency is about 95.6%. In summary, the inherent advantages of the proposed global modular architecture are the fast balancing speed, high balancing efficiency, small size, low cost, ease of control, and the simultaneous any-cells-to-any-cells equalization among any cells.