Inherently decoupled magnetic suspension in homopolar-type bearingless motors

The authors have proposed bearingless motors, that is, magnetic bearings co mbined with motors in the same stator. It is possible to reduce their shaft length compared with a conventional motor with magnetic bearings, and to a chieve higher rotational speed. Bearingless motors generate radial force by adding n +/- 2-pole flux on n-pole motor flux to make the flux distributio n unbalanced. Several types of bearingless motors have already been propose d, and most of them require variations of motor flux to be taken into accou nt to maintain stable radial position control. In this paper, homopolar-typ e bearingless motors are proposed and their radial force is analyzed. The r otor of a homopolar motor has two cores with salient poles, and each core i s magnetized in a single pole. The important characteristics that the radia l force does not vary in accordance with the rotor angle or the motor torqu e current are derived from analysis. It is confirmed by experiments that th e radial position can be controlled nearly independently from the rotationa l angle and torque.