Comparison Study of a Surface-Mounted PM Rotor and an Interior PM Rotor Made From Amorphous Metal of High-Speed Motors

Abstract

Currently, surface-mounted permanent-magnet (PM) rotors are more frequently employed than interior PM rotors in high-speed PM motors. It is mainly because the mechanical strengths of sleeve materials can be much higher than those of silicon steels. However, at high speeds, the current harmonics caused by pulsewidth modulation (PWM) converter induce high eddy current losses in PMs and sleeves when they are conductive. Moreover, because of the existence of nonmagnetic sleeves, the surface-mounted PM motors have very poor flux weakening abilities. Interior PM motors can not only avoid sleeves, but also reduce the influence of the PWM converters. Moreover, they can provide additional reluctance torque and have better flux-weakening abilities. A major drawback of interior PM rotors is their low mechanical strengths, which limit their surface velocities. In this article, high mechanical strength amorphous metal 2605SA1 is used to increase the surface velocity of an interior PM rotor. A surface-mounted PM rotor protected by carbon-fiber sleeve is designed to perform a comparison study. Both motors are built and tested. The advantages and disadvantages of the two motors in terms of mechanical, electromagnetic, and thermal behaviors are evaluated.