Several switched flux permanent magnet (SFPM) machines with mechanically movable flux adjusting technique are proposed, analyzed, and compared for applications which demand high speed and efficiency. By using ferromagnetic pieces-one per every stator pole or every alternative stator pole, which are named as flux adjusters (FAs) and located on the outside surface of the stator-the airgap flux density can be weakened and therefore the operation speed range and flux weakening capability can be improved. The influence of using all or alternative FAs on the open circuit results, electromagnetic performance, and torque-speed characteristics of the SFPM machine is investigated through three SFPM machines with different stator/rotor pole combinations, i.e., 12/10, 12/13, and 12/14. Moreover, although using FAs in all stator poles can significantly improve the flux weakening capability, alternative FAs can also achieve remarkable improvement although higher torque ripple is observed. Additionally, it has been found that the 12/13 combination is considered to be the most suitable candidate for alternative FAs technique. In addition to 2-D finiteelement analysis (FEA) and analytical methods, 3-D FEA results accounting for the end-effect are presented. Furthermore, experiments are performed to validate the results. Index Terms-Fluxweakening, mechanical flux adjusters (FAs), switched flux, variable flux. Locomotive Group (CSR). His current major research interests include the design and control of permanent-magnet brushless machines and drives for applications ranging from automotive to renewable energy. M. M. J. Al-Ani received the B.Eng. degree in electronic and electrical engineering from the University of Sheffield, Sheffield, U.K., in 2010, where he is currently working toward the Ph.D. degree from the Electrical Machines and Drives Research Group. His research interests include brushless permanent magnet machines for high speed applications, electrical and hybrid vehicles, and vehicles electrification. X. Liu (M'13) received the B.Eng. and Ph.D. degrees in electrical engineering

Realization of electrically boosted turbochargers requires electric motors capable of operating at very high speeds. These motors often use a permanent magnet rotor with the magnets retained within an interference fit external sleeve. Whilst it is possible to model such systems numerically, these models are an inefficient tool for design optimization. Current analytical models of rotors typically consider the stresses induced by the shrink fit of the sleeve separately from the stresses generated by centripetal forces due to rotation. However, such an approach ignores the frictional interaction between the components in the axial direction. This paper presents an analytical model that simultaneously accounts for interaction between the magnet and outer sleeve in both the radial and axial directions at designed interference and with the assembly subjected to centripetal and thermal loads. Numerical models presented show that with only moderate coefficients of friction and rotor lengths; axial load transfer between magnet and sleeve takes place over a short distance at the ends of the assembly. The paper then demonstrates how the analytical model aids definition of a feasible set of rotor designs and selection of an optimum design.

Surface-mounted permanent magnet (SPM) machines are preferred for high-speed aerospace applications over induction and switched reluctance machines, since they combine the advantages of high torque density and efficiency. Also, in aerospace applications, where low rotor weight and inertia are essential requirements, a permeable hollow shaft is proposed to replace the need for rotor back-iron and reduce the overall rotor weight. For rotor mechanical integrity, a retaining sleeve is commonly used, leading to thicker magnetic airgap. Furthermore, when permeable rotor endcaps are applied, an increase of the magnetic end leakage occurs, i.e. end-effect. In this paper, the influence of the rotor endcaps on the mechanical and electromagnetic performance of a high-speed SPM machine is investigated through 3D-finite element analyses (FEA). Also, different endcap thickness and different rotor shaft materials are investigated and compared in this work. Finally, a prototype of the SPM machine under study has been manufactured and tested. The comparison between simulation and experimental results is presented and discussed.

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This paper presents a comparative study of electromagnetic performance in switched flux permanent magnet (SFPM) machines with different topologies, i.e. conventional SFPM machines, multi-tooth, E-core and C-core SFPM machines. With the aid of 2D finite element analysis (FEA), the torque waveform, cogging torque, back-emf and d-and q-axis inductances are investigated and compared with emphasis on the torque-speed characteristics. In conventional SFPM machines, the influence of stator/rotor pole combination on the torque-speed characteristics is also investigated through 12/10, 12/13 and 12/14 SFPM machines. Compared with conventional SFPM machines, which exhibit limited speed range, infinite speed range is observed in multi-tooth, E-core and C-core SFPM machines, among which the highest average torque per ampere is achieved in E-core SFPM machine, albeit with relatively high torque ripples.