New rotor concept for sleeve-free high-speed motors over 125,000 rpm

This paper proposes a new rotor structure without sleeve for high-speed motors. As rotor losses are mainly dissipated over the air gap, a rotor sleeve based on fibre reinforced plastic poses a significant additional thermal resistance. Therefore the heat dissipation of a sleeve-free rotor benefits. In order to avoid the necessity of a sleeve, an interior permanent magnet (PM) structure is used. Considering the disadvantages at high frequencies on the PM and iron losses, as well as on the natural frequency of the rotor and on the modulation ration of the power electronic switches, a two-pole rotor is chosen. Amorphous material 2605SA1 is used for the high-speed rotor due to its lower losses and high yield strength. The electromagnetic properties of amorphous alloy and silicon steel are measured and compared. By comparing the mechanical stress on the rotor, the torque and rotor losses of four different rotor configurations, the feasibility of the proposed rotor design are confirmed. Finally, design optimization to reduce the rotor losses even further are illustrated.