Analytical modelling of the cogging torque of an axial flux permanent magnet synchronous machine

Abstract

Summary form only given. Axial-field machines have been widely used in the field of small power domestic applications. However, the cogging torque of these motors is known to influence significantly the behavior of this type of machines. Previous research work has been made in order to reduce the cogging torque in PM synchronous machine and it was demonstrated that it is greatly affected by the configuration of the stator, and magnetization distribution. So, in order to reduce this cogging torque, one needs to compute it for multiple configurations of stator core and rotor magnets. Cogging torque can be calculated accurately using the FEM. However this numerical technique does not easily allow a parametric study in an actual design. For this reason, analytical models have been developed. For the majority of them, the magnetic field in the airgap is calculated as the product of the magnetomotive force by the airgap permeance. The airgap permeance function when it is explicitly given, is calculated using the conformal transformation theory which is still limited to simple cases. In this paper an exact analytical solution for the magnetic field in an axial flux permanent magnet synchronous motor is presented. This method is based on the analytical resolution of Maxwell equations in the different regions and the cogging torque is then derived upon the Maxwell stress tensor method.