Two-dimensional magnetic field analysis of internal-rotor permanent-magnet motors

An improved analytical method is proposed for predicting magnetic field distribution in the air-gap and permanent-magnet regions of radial field topology of a brushless internal-rotor permanent-magnet motor. It is a two-dimensional model based on a conformal transformation approach where differences in the current density have been compensated for. The method involves a number of integrals of the vector potential, instead of the scalar potential found in the literature. The method is convenient for magnetic fields having complicated boundaries. The motor model is formulated in polar coordinates and accounts for the large effective air gap, resulting from the low magnetic permeability. Results of the motor analysis are compared with predictions from corresponding finite element analysis and other analytical techniques. They indicate the advantage of the developed approach over other recent analytical techniques.