Improved Torque Profile of a Doubly Salient Permanent Magnet Motor using Skewed Rotor Teeth and Sinusoidal Excitation

This paper presents the results of a three dimensional (3-D) finite element (FE) analysis carried out to get the improved torque profile of doubly salient permanent magnet (DSPM) motor by optimum skewing of rotor teeth and type of excitation from two types of excitations namely, rectangular and sinusoidal. Effect of skewing the rotor teeth on various performance characteristics like phase flux-linkage, self and mutual inductances, detent torque, average developed torque and torque ripple have been presented. It is observed that with the increase in the skew angle of the rotor pole the phase flux-linkage and the difference between the phase inductance for phase excitation supporting or opposing the permanent magnet excitation reduces. Result of harmonic analysis of the detent torque and developed torque for both type of excitation at various skew angles are presented from which it is observed that the 4l and its multiple torque harmonics are the predominant ones for both type of torque. It is also observed that for all skew angles the sinusoidal excitation of motor with two phase excitation mode is giving more average torque in comparison to the rectangular current excitation this is also true for torque ripple if the skew angles less than 24deg. It is also observed that skewing the rotor teeth by 12deg to 15deg with sinusoidal excitation will give higher average torque with reduced ripple, so becomes the best choice.