Evaluation of stator iron loss in tubular permanent magnet machines by three-dimensional finite element analysis

This paper evaluates the stator iron loss in a tubular permanent magnet (PM) machine equipped with a laminated stator core by three-dimensional (3-D) finite element (FE) analysis, and quantifies the influence of the laminated modules on the iron loss. The 3-D FE model accounts for the non-linear, anisotropic magnetisation characteristic of the laminated stator structure, and for the voids which exist between the laminated modules. Predicted results are compared with those deduced from an axi-symmetric (2-D) FE model which cannot account for the influence of the voids. It is shown that the no-load iron loss which is calculated from the 3-D FE model is virtually the same as that which is deduced from the 2-D FE model. However, on full-load the iron loss which is determined from the 3-D model is significantly lower than that which is predicted from the 2-D model, primarily as a consequence of the teeth and yoke being more highly saturated, due to the presence of the voids in the laminated stator core. However, if the width of the tooth and yoke sections of the I-shaped laminations from which the laminated modules are fabricated is increased to achieve the same effective tooth and yoke areas as in the 2-D model, the difference in the iron loss predicted from the 2-D and 3-D FE models becomes insignificant.