DAB Converter with Internal AC Heating Capability Using Trapezoidal Current Wave for Lithium-Ion Batteries in Electric Vehicles

Lithium-ion batteries (LIBs) in electric vehicles at low temperatures need proper pre-heating to avoid a decrease in their discharge capability. Internal ac heating techniques utilizing Joule heat generated by ac current flowing through an internal resistance of LIBs have been proposed as an efficient heating method. However, an additional inverter is necessary to generate ac currents, increasing system complexity and cost. Furthermore, traditional internal ac heating techniques using triangular or sinusoidal current waves are not ideal due to their relatively low rms values at a given peak current that eventually result in slow heating. This paper proposes a novel internal ac heating technique utilizing an existing inductor in ordinary dual active bridge (DAB) converters that are typically employed as an on-board converter. Depending on modulation techniques, the proposed converter can generate four types of trapezoidal current waves with different rms current values, all of which achieve shorter heating time than conventional internal ac heating. A charge-discharge power rating of 700W prototype with 40-W internal ac heating capability was built for a 48-V LIB. The experimental results demonstrated the proposed converter could heat up the LIB from -10°C to 0°C in 3.3 min.