Modeling and analysis of high-frequency alternating-current heating for lithium-ion batteries under low-temperature operations

In cold climates, preheating is necessary to improve the output power and available capacity of low-temperature lithium-ion batteries. Many internal Alternating Current (AC) heating approaches are available to heat low-temperature batteries with the advantages of fast heating speed, high efficiency, and good uniformity. However, due to the lower AC heating frequencies, the existing AC heating devices have the prominent features of bulky size and high cost, leading to difficult onboard implementation in electric vehicles. Therefore, this paper proposes a high-frequency AC heater based on buck-boost conversion and develops the high-frequency thermoelectric model based on the heat generation of the ohmic resistance and lithium ion transport. The experimental results verify the validities of the proposed high-frequency AC heating topology and thermoelectric model at different AC-heating frequencies and Root-Mean-Square (RMS) currents. This study shows increasing the AC-heating frequency at the same RMS current can dramatically improve the heating speed and efficiency due to the increased heat generation of the ohmic resistance and lithium ion transport, which does not cause further damage to batteries.