Influence of design parameters on cogging torque in permanent magnet machines

Abstract

The influence of various design parameters on the cogging torque developed by permanent magnet machines is inves- tigated. It is shown that the slot and pole number combination has a significant effect on the cogging torque, and influences the optimal value of both skew angle and magnet arc, as well as determining the optimal number of auxiliary teeth/slots. A simple factor, which is proportional to the slot number and the pole number and inversely proportional to their smallest common multiple, has been intro- duced to indicate the "goodness" of the slot and pole number com- bination. In general, the higher the "goodness" factor the larger the cogging torque. Index Terms—Cogging torque, electrical machines, machine de- sign, permanent magnet machines, speed ripple, torque, torque ripple.