Prediction of 3D eddy current loss in retaining sleeve of surface mounted permanent magnet machines

Abstract

This paper proposes a method based on the generalized image theory, for accurate prediction of 3-dimensional (3D) eddy current distributions in the retaining sleeves of permanent magnet machines and the resultant eddy current loss. The sleeve is unrolled down as a thin rectangular sheet of very small thickness, and the boundary conditions which govern the eddy current flow on its surfaces are represented by equivalent image sources in a homogeneous 3D space extending into infinity. By introducing a current vector potential, the 3D eddy current distributions in sleeve is derived analytically by employing the method of variable separation and the total eddy current loss in the sleeve is subsequently established. For resistance limited loss evaluation, 2D Sub-domain model considering stator tooth tips is employed to generate radial and tangential field information within the sleeve. The diffusion of the field variation along the axial direction is included to consider the eddy current reaction while evaluating the loss associated with high frequency armature harmonics. The results from the proposed method are validated from 3D time-stepped finite element analysis (FEA) of the sleeve eddy current loss for an 8-pole, 18-slot permanent magnet machine at no load, and on load with fundamental, 10 kHz and 20 kHz time harmonics in the armature currents.