Development of an external rotor surface permanent magnet machine with high continuous torque density

In-wheel motor fundamentally simplifies the mechanical transmission structure and is an ideal choice for the motor of electric vehicle. In the motor design process, not only the motor need excellent electromagnetic performance, but also the motor need good heat dissipation design. In this paper, the external rotor SPM machines are optimized for electromagnetic and thermal performance under the space limitation. By improving the heat dissipation structure of the end winding, the overall temperature rise of the external rotor SPM motor is reduced. The experimental results show that at the winding temperature of 140 degrees centigrade the continuous torque is increased by 25.2% with the improved cooling structure. The purpose of improving the continuous torque capability of the motor is achieved.