Strength analytical solution to ultra-high-speed permanent magnet rotor considering temperature gradient and segmental permanent magnet effect

Abstract

Ultra-high-speed permanent magnet synchronous motors usually adopt the rotor in which a sleeve is interference fitted onto a ring permanent magnet or segmental permanent magnets. The rotors are always subject to the extreme working condition (e.g. high speed and high temperature). In order to predict the strength of the rotor, this article proposes analytical models considering three types of stress sources such as interference fit, centrifugal force, and temperature gradient. Examples are calculated and discussed. Results show that the effect of the temperature gradient on sleeve stresses is slight; however, the influence of the temperature gradient on stresses of the permanent magnet and shaft is dramatic; for the rotor with a outer surface forced air cooling, the shaft will generate a large radial expansion which causes a addition pressure effect on the permanent magnet and sleeve to prevent loosening and stripping of the interfaces. Moreover, segmental permanent magnets are helpful to reduce stress. The study will give a useful hint for the optimal design and manufacture of the ultra-high-speed permanent magnet rotor.