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Title: Investigation of flux reversal permanent magnet machines
Author: Li, Huayang
ISNI:       0000 0004 7966 9937
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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Flux reversal permanent magnet (FRPM) machines, as one kind of stator-PM machines, are ideally suited to low-speed and high-torque applications due to their robust rotor structure, simple stator structure, and easy heat management. This thesis presents a thorough investigation into the FRPM machines, with particular reference to the working principle and performance improvement. Based on the air-gap field modulation theory, the PM magnetomotive force (MMF)-permeance model is adopted to analyse the working principle of the FRPM machines. The feature of multiworking harmonics in FRPM machines is revealed, i.e. all PM MMF harmonics together with the fundamental permeance contribute to the torque production. Based on the analytical model, the critical design parameters are parametrically investigated. It shows that the machine performance is sensitive to the PM thickness, since the PMs increase the equivalent air-gap length, thus restricting the field modulation effect and associated torque performance. Various aspects of improving the torque density of FRPM machines are then investigated in detail, including the PM polarities of adjacent teeth, the number of PMs on each stator tooth, alternate consequent-pole PM (CPM) topology, and toroidal-windings (TWs). It shows that opposite PM polarities of adjacent teeth are preferred compared to identical PM polarities, due to the more effective interactions between the PM and armature fields. Thanks to the additional back-EMF produced by the auxiliary PM MMF harmonic, a 76% higher torque density can be achieved in a prototype FRPM machine by properly increasing the number of PM pairs on each stator tooth. The FRPM machines with various CPM topologies are analysed and compared, from which the topology with the highest torque density is identified. Because of the improved armature field, the CPM-FRPM machine can exhibit more than 15% higher torque density than the conventional FRPM machine, even with halved PM volume. The FRPM machines with TWs are also proposed and compared with the machines using conventional concentratedwindings. For specific stator slot/rotor pole combinations, the torque density of the proposed machines with TWs can be improved by 80%, which resulted from the improved pitch factor. Finally, the performance of various FRPM machines are summarised and compared with the popular Vernier machine, which works based on the air-gap field modulation as well. Results show that although a large DC permeance component is utilised to produce torque in the Vernier machine, the FRPM machines can have competitive or even higher torque density, while their PM volumes are significantly reduced. All theoretical analyses are validated experimentally on various prototypes.
Supervisor: Zhu, Z. Q. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available