Performance characteristics of inset-type permanent magnet bearingless motor drives

Bearingless AC motors have attracted special attention in high speed motors for machine tools, compressors, turbomolecular and blood pumps, etc. The bearingless motor has the combined characteristics of an AC motor and magnetic bearings. It has been found that in a surface-mounted permanent magnet (PM) bearingless motor, the radial force can be increased with a decrease in PM thickness, increasing the possibility of demagnetization. In order to increase the radial force, a salient-pole PM bearingless motor, i.e., an inset-type PM bearingless motor has been proposed in this paper. Analytical expressions for the motor torque and radial forces have been derived. The motor and radial position control currents have been determined. There exists close agreement between the theoretical and experimental results. A prototype laboratory inset-type PM bearingless motor has been built and tested. It is successfully run at 10000 r/min with an output of 1.65 kW and an efficiency of 90.4%