Spectral modelling of force ripples in permanent magnet bearingless motors

The purpose of this paper is to propose an analytical model for the calculation of forces ripples in bearingless permanent magnet motor.

The model is based on a spectral modeling of the forces based on a spectral analysis of the air-gap flux density.

The proposed methodology allows the prediction of the ripples of the levitation according the design of the machine and the topology of the winding. It can be used in the design procedure of bearingless motor in order to avoid mechanical resonance of the rotor shaft.

This model cannot be used for high saturated machines.

The main originality of this paper consists in the evaluation of the field harmonics according to their sources and the contribution of the different harmonics to the force ripples. This can help the designer to focus on reducing or eliminating only the harmonics of flux density which create the force ripples.