Analysis of Eccentricity in Permanent-Magnet Tubular Machines

Translator eccentricity in permanent-magnet tubular machines is practically inevitable. It results in nonuniform air-gap magnetic-field distribution, which is inherently a 3-D problem. In this paper, the effects of eccentricity on field distribution and on the resulting unbalanced radial force are analyzed. Both no-load and load conditions are presented. The proposed mathematical model only requires the knowledge of the 2-D air-gap flux density distribution when the translator is at the balanced position. The analytical expression of the unbalanced radial force is derived together with the translator deformation analysis. The information of unbalanced radial forces acting on the translator and the translator displacement can be used for machine and bearing sizing. Analytically predicted and 3-D finite-element-calculated results are compared and validated by the experimental results obtained on a specially set-up test rig.