MODELING OF EFFECTS OF SKEWING OF ROTOR MOUNTED PERMANENT-MAGNETS ON THE PERFORMANCE OF BRUSHLESS DC MOTORS

This paper centers on the development of a method for computation of the parameters and performance of permanent magnet brushless dc motor drives, 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 2D axial symmetry in the resulting magnetic fields. This difficulty is overcome in this method of analysis by means of use of multiple cross-sectional 2D 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, as well as other performance characteristics, were found to be in excellent agreement with test data performed on an example 1.2 hp, 120 Volt brushless dc motor drive system.