Mechanical strength analysis and optimization of metallic sleeve in high-speed permanent magnet synchronous machines

Metallic sleeves are widely used to ensure the mechanical integrity of rotors in high-speed permanent magnet (PM) synchronous machines (HSPMSM). However, in traditional high-speed rotors, the PMs which are very weak in tensile stress cannot be well protected by sleeves. Furthermore, the material properties of both the sleeves and PMs cannot be fully used. As a result, the high-speed running range of the machines are limited by the mechanical strength for a given rotor size. In this paper, taking a 230-kW 35-kr/min prototype as an example, the mechanical strength issues of the rotor are investigated by analytical method and finite element analysis (FEA). In order to overcome the unbalanced protective effect of the sleeve and make fully use of the materials, an optimal sleeve, as well as an improved rotor structure, is presented. The comparison results show that the optimized sleeve has well balanced protective effect to the PM as well as good utilization of materials, with a resultant increase in maximum speed of nearly 40% with respect to the prototype.