Reduction of cogging torque and back EMF harmonics in modulated pole machine by variations in tooth span

Modulated pole (transverse flux) machines are known for their torque density and can take advantage of mutual flux paths to further increase the torque density of this class of machine. This paper presents a retrospective design investigation into a combined phase machine conducted in order to reduce the harmonic content of the back EMF and the cogging torque of the machine; two common problems with modulated pole machines. A method is proposed and it is shown that by changing a simple geometry such as the tooth span, cogging torque, torque ripple and harmonic content can all be significantly reduced without a significant effect on the overall torque output.