Rotor design for a high-speed high-power permanent-magnet synchronous machine

Abstract

Permanent-magnet synchronous machines (PMSMs) are considered a very promising machine type for high-speed applications nowadays. As permanent-magnet (PM) materials are generally fragile, a high strength sleeve is required to protect the PMs from damage due to extreme centrifugal forces. The rotor sleeve occupies space of the effective air gap of the PMSMs, so 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-electromagnetic design method is presented for the rotor of a high-speed PMSM designed for 200 kW at 40,000 rpm. Three commonly used sleeve materials are investigated and their mechanical performances are analyzed. The mechanical strength limits for the proposed machine are calculated, as well as the EM design limits. The optimal dimensions for the rotors with different sleeves are then obtained by combining their strength and EM limits. The EM, thermal and rotor dynamic performances of the designed rotors are analyzed in order to select the best rotor type. In the end, a new rotor topology is proposed to reduce the rotor eddy current losses. The new rotor topology is characterized by a multi-layer sleeve which is thinner than a single-layer sleeve. The rotor losses are significantly lower in the new rotor and easier to be cooled.