Study of characteristics of various structures in axial-gap PM motors

High output power and small size are required for motors intended for vehicle drive applications. Therefore, permanent magnet synchronous motors (PMSMs) are the current standard for EV/HEV drives. There are two types of PMSMs: axial-gap motors and radial-gap motors. Axial-gap motors have their air gap in the axial direction and the coil end in the radial direction. Hence, the axial-gap motor is suitable for thin motors. In this paper, four types of axial-gap motors and two types of radial-gap motors of the same size (including the coil end) are examined to find the motor with thin shape, high output power, and high efficiency. Based on the results, the axial-gap motor with a concentrated winding stator and surface permanent magnet (SPM) rotor has the highest efficiency of the four axial-gap models. However, in comparison with radial-gap motors, the radial-gap motor with the concentrated winding stator and SPM rotor has the largest maximum torque in the low-speed region. Also, the efficiency of the radial-gap motor is high due to its small winding resistance.