Development of homo-polar type bearingless motors

The authors have proposed bearingless motors, that is, magnetic bearings combined with motors in the same stator. It is possible to reduce their shaft length compared with a conventional motor with magnetic bearings, and achieve higher rotational speed. Bearingless motors generate radial force by adding n±2-pole flux on n-pole motor flux to make the flux distribution unbalanced. Several types of bearingless motors have already proposed, and most of them require to take variations of motor flux into account to control radial position stably. In this paper, homo-polar type bearingless motors are proposed and their radial force is analyzed. The rotor of a homo-polar motor has two cores with salient poles, each core is magnetized in a single pole. The important characteristics that the radial force doesn´t vary in accordance with the rotor angle nor the motor torque current is derived from analysis. It is confirmed by experiments that the radial position can be controlled nearly independently from the rotational angle and torque