Analytical Multi-Element Rotor Thermal Modelling of High-Speed Permanent Magnet Motors Accounting for Retaining Sleeve

This paper proposes an analytical multi-element thermal modelling method for predicting the sleeve and magnet thermal fields for high-speed permanent magnet machines (HSPMMs). The analytical model is developed based on the conduction heat equations and the continuity equations of heat transfer. The rotor temperature distributions and hotspots can be accurately predicted with the aid of the boundary conditions from a lumped-parameter thermal model. The proposed method is applied to investigate the influences of different PM segmentations and rotor sleeve materials on the rotor thermal performance. Based on a 3-slot/2-pole HSPMM, it is shown that the PM segmentation parallel to the magnetisation direction together with the carbon fibre sleeve can significantly ease the rotor thermal stress. The finite element analyses and experiments have been used for validation.