DAB Converter Integrating Trapezoidal-Wave Internal Heating Inverter for Automotive Lithium-Ion Batteries at Subzero Temperatures

Adequate preheating for electric vehicles' lithium-ion batteries (LIBs) in cold climates is indispensable to prevent a decrease in cruising distance. Internal ac heating techniques utilizing Joule heat originating from LIBs' internal resistances have been proposed as an efficient and rapid heating method. However, an additional inverter is necessary to generate ac currents, resulting in increased system complexity. Furthermore, conventional triangular and sinusoidal current waves are not ideal as their rms values at a given peak current are relatively low. This article proposes a dual active bridge (DAB) converter integrating an ac internal heating inverter. A full-bridge circuit is utilized not only for the DAB converter but also for the ac heating inverter, achieving a simplified system. A novel PWM technique is also proposed to generate a trapezoidal current wave that achieves higher rms currents at a given peak current. A 400-W prototype with 50-W internal heating capability was built for a 48-V 3400-mAh LIB. Experimental results demonstrated that, in addition to the bidirectional power conversion capability, the trapezoidal wave could warm up the LIB from -10 degree celsius to 0 degree celsius in 2.6 minutes.