Five-axis magnetic suspension with two conical air gap bearingless PM synchronous half-motors

A novel type of “bearingless” permanent magnet (PM) synchronous motor is presented. The motor consists of two conical air gap bearingless PM half-motors, mounted on a single shaft. Each conical stator houses two separate three-phase distributed AC windings with different magnetic pole pair counts. The motor winding has the same pole count as the PM rotor for the generation of the torque and the axial force. For time invariant radial levitation forces, the second winding (the levitation winding) must have one pole pair more or less than the rotor PM field. It must be fed with the same electrical frequency as the motor winding. With this drive arrangement all six degrees of freedom of the rigid rotor can be actively stabilized and controlled without using any further active magnetic bearings. A prototype with a rated mechanical output power of 1 kW at a rated speed of 18 000 rpm has been designed and built, in order to validate the theory.