Analysis of torque developed in axial flux, single-phase brushless DC motor with salient-pole stator

An analysis of the torque developed by a single-phase disc brushless permanent magnet motor with salient-pole stator is presented. The machine represents a new family of brushless disc motors with the starting torque issue appearing to be most challenging. To produce a starting torque, the permanent magnets on one of the rotor discs are distributed nonuniformly. However, this significantly distorts a shape of the cogging torque versus rotational angle characteristic which, in turn, affects a waveform of the overall torque. A three-dimensional (3-D) finite-element model is used for the purpose of determining of angular variations of the torque developed by the motor. To find how the torque varies with time, a model of the source-inverter-motor circuit is developed. A simulation study on an influence of the commutation angle on the electromagnetic torque is also a subject of this paper. The results obtained show that the motor performance can be improved by a proper selection of the current commutation angle to reach the maximum efficiency. The simulation results are in good agreement with measurements obtained from a prototype motor.