Radial force modeling for bearingless motors based on analyze of field origins

Abstract

This article proposes a global harmonic analysis of normal and tangential field components in air gap of multiphase bearingless permanent magnet motor topology to determine the radial force. This allows establishing the semi-analytical expressions of the radial force considering the location of field sources. The accuracy of the model is verified by full finite element method model using a statistic approach. An important result of this approach of modeling is that it permits to choose the most convenient topology for the bearingless permanent magnet motors by taking into account the location of the field sources in stator and rotor. In addition, the semi-analytic model allows predicting the force waveforms according to the stator and rotor topologies. The analysis of two different rotor topologies is carried out and it highlights the influence of the tangential component of the air-gap magnetic field on the motor performances. Moreover, the influence of the radial or parallel magnetization of the rotor magnet on the force ripples is discussed. The reduction of CPU time using the semi-analytical model makes it suitable to be implemented in a design optimization process.