Basic characteristics of a consequent-pole-type bearingless motor

In this paper, we describe the basic characteristics of a consequent-pole bearingless motor. The consequent-pole-type rotor has buried permanent magnets (PMs) polarized in the same radial direction. We carried out an analysis to find the optimum pole number for the machine to produce stable magnetic suspension. The results indicate that there is decoupling of the radial suspension forces from the drive torque when eight or more poles are used. Here, we compare the torque and suspension force generation with those of a conventional surface-mount PM rotor. The suspension force is several times higher for the consequent-pole rotor; however, the torque decreases by 12%. We built a test machine and confirmed the torque and suspension characteristics. We also compared the test machine with other conventional bearingless motors.