Evaluation of Manufacturing Dissymmetry Effects in Axial Flux Permanent-Magnet Machines: Analysis Method Based on Field Functions

Abstract

An analytical method is presented to evaluate the field and global quantities for the operation and design analysis of axial flux permanent- magnet (PM) machines. The method, of general applicability, is based on the definition and superposition of suited field functions, able to accurately model the different singularities of the studied device: PM field distribution, effects of slotting, and radial end effects. Selected explorative FEM analyses are used in order to investigate the field functions shape and to help in identifying their structure and parameters. Then, the flux density distribution is obtained, as a function of the rotor position, taking into account some manufacture dissymmetry effects, such as air-gap offsets and PM rotor disk inclinations. This approach allows to analyze the effect of dissymmetry on the circulation of current among winding parallel paths in no-load operation. Moreover, by using theMaxwell stress tensor, the stress distribution is evaluated, as well as the resultant axial forces and the bending torques on the shaft due to the rotor disk tilts. Several FEM simulations show the soundness of the proposed method, which exhibits high accuracy and great evaluation speed

Effects of manufacturing dissymmetry in axial flux PM machines

“…These fluxes can be evaluated as the surface integral of the flux density B qz (q = L or R) within each tooth pitch τ tk . Since the field function approach is intrinsically 2D, the surface integral reduces to a line integral along the reference line c av : the radial end effects are taken into account with suited corrective coefficient, identified by FEM [6].…”

“…In (10) η σ (g q (θ s , θ sr )) is a FEM identified correction factor, which takes into account the radial effects and allows an accurate evaluation of the resulting forces and torques [6]. Finally, the resultant force acting on the stator teeth is given by the difference between F R and F L :…”

“…In [6], the method was validated by both 2D and 3D FEM simulations: in both cases, the results were good. In this paper, a case study is presented, concerning the effects that various kind of assembly dissymmetry cause on two quantities: the circulation currents in parallel winding paths at no load and the mechanical stresses together with the resulting axial forces and bending torques on the machine shaft and disks.…”

“…Nevertheless, in the design stage it is worthwhile a method which allows to estimate in a quite simple way the electrical quantities and the mechanical stresses due to dissymmetry. In a previous paper [6] a suited methodology was proposed, where the electrical and mechanical quantities are evaluated starting from an accurate analytical reconstruction of the air gap flux density. The field behavior is obtained by means of a "field function" approach [7]- [9].…”

Effect of unbalanced and inclined air-gap in double-stator inner-rotor axial flux permanent magnet machine

“…Static eccentricity changed the amplitude of back electromotive force (EMF) and it was proposed to use EMF curve for fault detection during manufacturing and assembling. The air-gap asymmetry arisen from offset or inclination in an inner-stator double outer-rotor AF machine is studied in [9,[17][18][19]. In [9] relevant mechanical stresses due to the electromagnetic attraction between the stator and the rotor parts due to slight air-gap asymmetries were analyzed based a simplified 2D rectified geometry using a circuit model.…”