Rotor Design and Eddy-Current Loss Suppression for High-Speed Machines With a Solid-PM Rotor

High-speed permanent-magnet (PM) machines are promising for many industrial applications. The main design challenge of high-speed PM machines comes from the PM rotor design due to the low strength and high thermal sensitivity of PM materials. In this paper, the mechanical constraints and speed limits for a high-speed rotor topology are derived with analytical equations. Thereafter, a case study is done to design an 80 kW, 80 000 r/min PM machine. Analysis results show that the high rotor eddy-current loss is one of the key factors contributing to the overheat of the PMs. Hence, a hybrid sleeve topology, which contains an inner titanium cylinder and an outer cylinder made up of carbon fiber composite, is proposed to suppress the rotor eddy-current losses. The optimal dimensions of the hybrid sleeve are obtained by finite element analysis. Thereafter, a comparison among the proposed and two other sleeve topologies, namely, the copper clad sleeve and grooved sleeve, is done from the point of view of their rotor eddy-current losses, rotor temperature rise, mechanical stress, and critical speed. The results indicate that the hybrid sleeve gains an advantage over the other two topologies. For the designed case, the rotor eddy-current losses and temperature rise are decreased by 66.4% and 73 °C, respectively, by using the hybrid sleeve. Furthermore, a reduction of 14.5% for the rotor maximum stress is obtained with the hybrid sleeve, while the rotor's first critical speed has little reduction.