Eddy current loss analysis in the rotor magnets of permanent magnet spherical motor

The rotor magnets of the permanent magnet spherical motor (PMSM) have a structure of spherical cone, and all of the stator coils are distributed on the inner surface of the stator shell independently of each other. In view of these characteristics, a three-dimensional (3-D) analytical model is presented to study the eddy current loss of magnets in the PMSM. And this model combines the double Fourier series decomposition and the magnetic vector potential method. First, the current density distribution at the inner diameter of the stator is described by employing the double Fourier series decomposition. With the current density distribution and other boundary conditions, the unique solution of magnetic vector potential is obtained by solving 3-D Laplace's equations. Further, the analytic expression of PM eddy current loss in the PMSM is derived. This model considers the effect of harmonics, and the influence of different motor parameters on the eddy current loss has been analyzed. The results of analytical method and finite element method (FEM) are compared, proving the effectiveness of the proposed analytical model. ©, 2015, Chinese Machine Press. All right reserved.