Abstract
This paper presents a novel bearingless synchronous reluctance slice motor topology that contains no permanent magnets. The rotor with two iron poles and flux barriers is levitated and rotated through a stator winding system with six coils wired as two three-phase systems. A constant rotor-oriented magnetization current is applied to generate a magnetic bias flux. The system can be controlled similar to a bearingless permanent magnet synchronous slice motor and provides passive stabilization of axial and tilting movements of the rotor. The motor topology is discussed in detail and a prototype implementation is presented. Its performance with regard to passive properties, achievable torque, controllability, and wide air gap suitability is benchmarked against two other designs that contain permanent magnets either in the rotor or the stator. A loss analysis of all topologies is performed and suitable application areas are identified. The proposed design provides an interesting alternative to existing bearingless slice motor topologies in applications that require high rotational speeds, high process or ambient temperatures, or a disposable low-cost rotor with short exchange intervals.
Highlights
Bearingless motors feature a magnetically levitated rotor and a stator with a magnetically integrated bearing function [1]
As such motors are usually limited by thermal constraints, the torque and active radial forces are compared at the same motor losses, which consist mostly of ohmic winding losses, while iron losses are at a negligible level due to the low rotational speeds
To obtain the magnetic bias flux that is necessary for the passive stabilization of the rotor, the synchronous reluctance motors (SynRM) generates half of the ohmic full-load losses, while the permanent magnet synchronous motors (PMSM) and flux switching permanent magnet (FSPM) topologies both generate no ohmic losses
Summary
Bearingless motors feature a magnetically levitated rotor and a stator with a magnetically integrated bearing function [1]. Each with a concentrated motor winding for combined generation of torque, radial bearing forces, and premagnetization of the machine are used Such a setup results in improved thermal properties and low stray fields. RRo rRo of 0.1 is used, where δmag, rRo, and rSi denote the magnetic air gap length, the outer rotor radius, and the inner stator radius, respectively (cf Fig. 2) This value is similar to that used in existing bearingless motor topologies with rotors featuring. [29], Chapter 3 for more details) Based on this simplified model, it can be seen that a magnetization current Imag leads to attracting forces between the stator teeth and the rotor of the considered SynRM topology that increase quadratically with Imag. It should be noted that field weakening in PM machines could be used to achieve a similar behavior, within significantly narrower limits
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