Rotor Design for High-Speed High-Power Permanent-Magnet Synchronous Machines

Permanent-magnet synchronous machines (PMSMs) are considered a very promising machine type for high-speed (HS) applications. As permanent-magnet (PM) materials are generally fragile, a high-strength sleeve is required to protect the PMs from damage due to the extreme centrifugal forces. The rotor sleeve occupies space of the effective airgap of the PMSMs; therefore, it is difficult to perform the electromagnetic (EM) design without an accurate estimation of the sleeve thickness, which is determined by mechanical issues. In this paper, an integrated mechanical- EM design method is proposed for the rotor design of HS PMSMs. A 200-kW 40 000 r/min surface mounted PM machine is taken to illustrate the design procedure of the proposed method. Three commonly used sleeve materials are investigated and their mechanical performances are analyzed. The optimal dimensions for the rotors with different sleeves are obtained by considering the strength and EM limits. The EM, thermal, and rotor dynamic performances of the designed rotors are analyzed and compared. In the end, a new rotor sleeve topology is proposed to reduce the rotor eddy current losses.