Investigation of Magnetically Geared Stator Permanent Magnet Machines

Stator-permanent magnet (PM) (Stator-PM) machines include doubly salient PM, flux reversal PM (FRPM), and switched flux PM (SFPM) machines, in which both the PMs and armature windings are placed in the stator, whilst there is neither PM nor coil in the rotor. They have been the subject of much interest over the last 20 years. The operation and interaction mechanisms between the open-circuit and armature excitation magnetomotive forces (MMFs) in stator-PM machines have not been well described, however, which will be explained by the magnetic gearing effect in the first part of this thesis. It is found that similar to magnetic gears and magnetically geared (MG) machines, conventional single-stator-PM machines operate based on the modulation effect of the rotor to the open-circuit and armature excitation MMFs. It is also found that more than 95% of the average electromagnetic torque in SFPM machines is contributed by several dominant open-circuit and armature excitation air-gap field harmonics. The magnetic gearing effect in the partitioned stator SFPM (PS-SFPM) machines, which was proposed recently based on the magnetic gearing effect in the conventional single stator SFPM machines, is also investigated in this thesis. The partitioned-stator-PM machines also operate based on the magnetic gearing effect. Furthermore, over 93% of the electromagnetic torque generated in both the outer and inner air-gaps in the PS-SFPM machines is contributed by the dominant air-gap field harmonics.
Consequent-pole PM topology and overlapping armature winding topology for the partitioned stator FRPM (PS-FRPM) machines, based on the magnetic gearing effect in the partitioned-stator-PM machines, are investigated in this thesis. By applying consequent-pole PM topology, about a third of the PM volume can be saved, but the torque density and efficiency are similar. For the overlapping armature winding topology, higher torque density, smaller loss, and hence larger efficiency etc. can be achieved when the machine stack length is relatively long.
Finally, the PS-FRPM machines and the conventional MG machines, both of which have surface-mounted PMs, are compared in terms of electromagnetic performance. Compared with conventional MG machines, PS-FRPM machines have a smaller flux-leakage and hence a higher torque density and a larger power factor due to their smaller PM pole-pair number and iron piece number.