Comparative analysis of spoke-type, consequent-pole and hybrid-pole permanent magnet machines

In recent years, consequent-pole permanent magnet (CPM) machines draw much attention due to their high utilisation ratio of permanent magnet (PM) material. However, they have some disadvantages, such as the even-order harmonics of airgap flux density, which may cause asymmetric phase back-EMF and the increase of torque ripple. In this study, a novel hybrid-pole PM (HPM) machine is proposed, in which the rotor combines consequent-pole and spoke-type PM rotors. The working principle of the proposed HPM machine is analysed based on the equivalent magnetic circuit, and validated by the finite-element method. Then, the electromagnetic performance of the HPM machine is compared with those of the existing CPM and spoke-type PM machines. It is shown that the HPM machine obtains similar average torque, PM utilisation ratio, torque ripple and efficiency to the spoke-type PM machine, whilst it has a higher PM utilisation ratio and much lower torque ripple than the conventional CPM machines. Finally, these analyses are validated by the tested results of a 9-slot/6-pole HPM machine.