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Title: Investigation of high speed permanent magnet motors
Author: Ma, Jie
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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This thesis investigates the electromagnetic performance of high speed permanent magnet (PM) motors, with particular reference to the mitigation of parasitic effects, the influence of key design parameters and the improved optimization method. In order reduce the parasitic effects, i.e. unbalanced magnetic force (UMF) and on-load magnet eddy current loss which are the most undesirable drawbacks of 3-slot/2-pole high speed PM motors, the motors with several different types of auxiliary slots are investigated and compared. It shows that the auxiliary slots with the optimal size and position can reduce the rated on-load UMF and the rated on-load magnet eddy current loss over 95% and 80%, respectively, with only a slight sacrifice of output torque. In addition, the influence of working conditions, drive modes, slot opening widths and rotating directions on the parasitic effects is studied as well. Moreover, the proposed magnet eddy current loss reduction method can be also applied to other motors with different slot/pole number combinations and winding configurations. In addition, as one of the most important design parameters, the influence of magnet thickness is investigated comprehensively. It shows that 3-slot/2-pole high speed PM motors with thicker magnet can benefit from lower on-load UMF, lower magnet eddy current loss as well as better demagnetization withstand capability. The influence of magnet thickness on other performances, e.g. the flux linkage, the back electromagnetic force (EMF) and the inductance, etc., is also studied. Finally, a new analytical optimization method is presented. Different loss constrains are taken into account in the optimisation, i.e. stator loss limitation only, rotor loss limitation only and both stator and rotor loss limitations. It shows that these loss constrains can significantly affect the optimal split ratio and the motor performance. By considering the influence of rotor loss, especially the rotor eddy current loss, the optimal split ratio is increased significantly in some scenarios. The output torque is calculated analytically and the influences of several key design parameters on the optimal split ratio, e.g. the maximum stator flux density, slot/pole number combinations and magnet materials, etc., are investigated in details.
Supervisor: Zhu, Zi-qiang ; Gladwin, Dan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available