Improving the torque quality of a modulated pole machine

Abstract

The research work carried out in this thesis is collaboration between Newcastle University and Höganäs AB, Sweden. A topology, termed ‘Separate Phase MPM’ was initially developed by Newcastle University and Höganäs where the machine takes advantage of mutual flux paths in order to increase the torque density of the machine, however had high cogging torque and back EMF harmonic content. The work presented in this thesis was carried out with an overall aim to minimise the cogging torque and back EMF harmonics in the Modulated Pole Machine (MPM) topology aimed toward electric bicycles. Various techniques are proposed and verified in this thesis to reduce the magnitude of unwanted voltage and torque harmonics, providing a smoother riding experience. Finite Element Analysis was carried out using Infolytica MagNet® on various design techniques which ultimately stemmed in 24 motor prototypes being constructed and tested during this PhD. The measured results are compared with each other to approve the technique that provides the optimum motor performance. It is shown that the peak cogging torque is reduced by 90% while the back EMF harmonics are diminished too, with a minor 2% reduction in mean back EMF. The efficiency and peak torque of the optimum motor is 8% and 10% higher, respectively, when compared with the base motor used in this study.