Simplified Modeling of an Innovative Heating Circuit for Battery Pack Based on Traction Motor Drive System

Alternating current (AC) heating is an efficient and homogeneous manner to warm Lithium-ion batteries (LIBs) up. The integrated design of AC heating combined with the motor drive circuit has been studied by many scholars. However, the problems of excessive heating frequency (>1kHz) and zeros torque output of the motor during the heating process have not been solved. High-frequency AC excitation may be detrimental to the battery because the effect of high-frequency AC excitation on the state of health of the battery is unknown. In addition, although the zero-torque output can be realized by controlling the q-axis current to zero, the torque ripple is still difficult to eliminate in a real-world application. To further solve the above problems, the motor’s neutral conductor is pulled out and connected to a large capacitor to increase the current amplitude of the AC heating at low frequencies. To quickly evaluate the AC that the heating system can generate, a simplified equivalent circuit model is established. And a new numerical solution algorithm is proposed to solve the nonlinear model. Finally, the capability of the system is evaluated using a specific set of parameters. The results show that the proposed algorithm can approximately solve the nonlinear model with a limited number of iterations. And the evaluation results of the heating system indicate that the heating system can quickly heat the battery pack. Compared with other works, the theoretical temperature rise rate is greater than 2.29°C/min. The battery pack heating scheme will promote the application of electric vehicles (EVs) in cold regions.