Magnetic field analysis of permanent magnet motors

Brushless permanent magnet motors work with a large effective airgap due to the low magnetic permeability, very close to that of air, of modern permanent magnets. This paper presents a developed model for these motors that takes into account the large difference which exists between the rotor and the stator iron radii. The conventional developed model, for small airgap motors, results as a particular case of the present one. The model is based on a logarithmic conformal transformation that links the motor cylindrical coordinates with the rectangular ones of its developed model. The permanent magnets are also transformed by a scale factor. The connection between magnetic fields is described. Numerical results show the validity of the proposed model. Moreover, a theoretical proof treating the magnetic fields of a current line is also presented.