Modeling of effects of skewing of rotor mounted permanent magnets on the performance of brushless DC motors

A method for computation of the parameters and performance of permanent-magnet brushless DC motor drives is developed in which the concept of skewing is implemented through the geometries of permanent magnet mounting on the rotor and not through the usual skewing of the armature slots. This technique of permanent-magnet mounting eliminates the 2-D axial symmetry in the resulting magnetic fields. This difficulty is overcome by the use of multiple cross-sectional 2-D finite-element field computations, coupled with a concept of an artificial mutual-coupling inductance between the armature phase windings and the rotor-mounted permanent magnets for induced EMF and torque computations. The computed induced EMF waveforms, motor phase winding current waveforms, and other performance characteristics are found to be in excellent agreement with test data obtained using a 1.2 hp, 120 V brushless DC motor drive system