Selective Module-to-Cell Equalizer With Internal AC Heating Capability for Automotive Lithium-Ion Batteries at Subzero Temperatures

Preheating for automotive lithium-ion batteries (LIBs) is indispensable to enhance cruising distance at subzero temperatures and to improve fast-charging performance. Internal ac heating techniques that utilize Joule heat originating from LIBs’ internal resistances are an efficient heating method. However, an additional inverter is necessary to generate ac currents for LIBs, increasing the system complexity and cost. This article proposes an integrated cell equalizer that operates either in a cell equalization mode or internal ac heating mode. The proposed equalizer is based on a selective module-to-cell equalizer using a dual active bridge (DAB) converter. The DAB converter in the equalization mode exchanges energies between the LIB module and cells. In the ac heating mode, a winding inductance of a transformer resonates to generate ac heating currents for the LIB module. A prototype for a 3400-mAh 12-cell module was built and tested. Experimental results demonstrated the successful internal heating capability and cell equalization performance.