An Automotive Onboard AC Heater Without External Power Supplies for Lithium-Ion Batteries at Low Temperatures

In cold climates, lithium-ion batteries suffer severe power/energy loss, bad performance, and reduced life cycle. Many internal ac heating strategies have been proposed to provide fast heating with a higher efficiency and better uniformity. However, the ac current is typically generated by an offboard equipment with grid power supply, which is a main bottleneck of the ac heating applied to electric vehicles. Therefore, an automotive onboard ac heater is proposed to heat lithium-ion batteries at low temperatures without the requirement of external power supplies. Only one pair of complementary pulse width modulation signals is employed to drive the proposed ac heater, and the heating speed can be online regulated by controlling the switching frequency. Particularly, the heating time can be reduced drastically by combining two heaters in interleaved parallel without causing harm to the batteries. In addition, the heating circuit can also realize the automatic balancing for battery cells if needed. Experimental results show that the proposed interleaved parallel heater, by circulating an ac current with the amplitude of 3.1 C and the frequency of 833 Hz, can heat lithium-ion batteries from -20 to 0 degrees C within 5.9 min, consuming about 5% of cell energy.