High Torque Density Design Investigations of High-speed Homopolar Type Permanent Magnet Motor

This paper presents design studies on a stator for a high-speed homopolar type permanent magnet motor that can be applied to a super charger for automobiles, and cordless stick vacuum cleaners, among others. The stator of the motor comprises electromagnetic steel cores, permanent magnets and concentrated windings. The rotor is composed of only electromagnetic steel cores without any retaining ring on the surface, thereby offering high mechanical strength suitable for high-speed applications with no increase in manufacturing cost and eddy current loss. However, the homopolar type permanent magnet motor treated in this study tends to have low torque density due to its three-dimensional magnetic circuit inherent to this type of motor. To improve the torque density, the designs of sintered Nd-Fe-B and bonded Nd-Fe-B permanent magnets were investigated from the viewpoints of reduced eddy current loss, higher maximum torque, and less cost. Finally, experimental studies on a prototype of the designed motor showed that the test results are in good agreement with corresponding analytical results. Therefore, the design approach adopted in this study is useful for examining the torque density improvement of the homopolar type permanent magnet motor.