Cell Voltage Equalizer with AC Internal Heating Capability for Automotive Lithium-Ion Batteries

Lithium-ion batteries (LIBs) for electric vehicles (EVs) require a cell voltage equalizer and a heater for preheating to avoid a decrease in cruising distance at low temperatures. Internal ac heating techniques can heat LIBs uniformly and efficiently by utilizing Joule heat generated by LIBs’ internal resistances. However, the LIB system using internal ac heating techniques needs an additional inverter to generate an ac current, resulting in increased system complexity and cost. This paper proposes an equalizer with an internal ac heating capability. The proposed equalizer employs a dual active bridge (DAB) converter and utilizes a half-bridge circuit of the DAB converter as an inverter, achieving a simplified system and reduced cost compared with the LIB system containing an additional inverter. Experimental results demonstrated that, in addition to the equalization capability, the proposed equalizer could warm up the LIB from −10℃ to 0℃ using the ac current generated by the inverter.