Bearingless Single-Phase Motor with Concentrated Full Pitch Windings in Interior Rotor Design

Bearingless motors are commonly used in special applications with high demands on speed range, lifetime, cleanness or tightness. The integration of distributed 3-phase motor windings and 3-phase radial magnetic bearing windings with sinusoidal current density distribution leads to a high number of stator coils and high manufacturing costs in comparison with ordinary ball bearing motors. For this reason a new bearingless low cost motor has been developed. It is a single-phase motor with only four concentrated full pitch coils for controlling both torque and levitation. The speed and position control is performed by superposition of lateral force and radial force current components in the windings. Owing to the nonsinusoidal stator current density distribution the Maxwell and Lorentz force vectors move on elliptical locus curves when the permanent magnet rotor is rotated at constant current. Thus special transformation functions have to be used for control of rotor position. The stabilization of the rotor disc position in axial and tilting direction is passively achieved by the magnetic tensible force, supported by suitably selected diameter / axial length ratio of the magnetic components. Possible applications of the bearingless single phase motor are electrical machines with low starting torque like fluid pumps, vacuum pumps, fans or blowers.