Significance of Anisotropic Thermal Expansion in High Speed Electric Machines Employing NdFeB Permanent Magnets

Ram Kumar, Antonino La Rocca, Gaurang Vakil, David Gerada, Chris Gerada and Baylon G. Fernandes
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Ram Kumar: Power Electronics, Machines and Control Group, University of Nottingham, Nottingham NG7 2RD, UK
Antonino La Rocca: Power Electronics, Machines and Control Group, University of Nottingham, Nottingham NG7 2RD, UK
Gaurang Vakil: Power Electronics, Machines and Control Group, University of Nottingham, Nottingham NG7 2RD, UK
David Gerada: Power Electronics, Machines and Control Group, University of Nottingham, Nottingham NG7 2RD, UK
Chris Gerada: Power Electronics, Machines and Control Group, University of Nottingham, Nottingham NG7 2RD, UK
Baylon G. Fernandes: Department of Electrical Engineering, Indian Institute of Technology-Bombay, Mumbai 400076, India

Energies, 2021, vol. 14, issue 22, 1-18

Abstract: Many high speed applications employ a surface permanent magnet (PM) machine topology with a retaining sleeve due to its robustness and ability to achieve high overall peripheral speeds as well as efficiencies. One often overlooked feature in the mechanical design of such machines, which has not achieved sufficient attention to date is the anisotropic thermal expansion of rare earth magnets, the degree of which varies for different magnet technologies. This paper investigates the effects of the aforementioned on the mechanical design of a high speed PM spindle machine with NdFeB magnets. The maximum allowable interference is found to be limited by the working temperature of the magnets while the minimum required interference is increased due to their anisotropic thermal expansion. Based on this, appropriate conditions are formulated to integrate a Neodymium Iron Boron (NdFeB) PM in high speed rotors. These modifications considering the shaft together with the magnet anisotropic thermal expansion are included in a proposed rotor design and validated using simulations in ANSYS mechanical environment.

Keywords: anisotropic thermal expansion; high speed; NdFeB permanent magnet; PMSM; retaining sleeve (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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