Optimization design of rotor structure for high speed permanent magnet machines

Permanent magnet (PM) machine is especially being employed in high speed machines due to its simple structure and high power density. Nowadays, the sintered neodymium-iron-boron (Nd-Fe-B) material is used in most of PM machines. This kind of PM material has large compression strength but small tensile strength, and can not withstand the large centrifugal force due to the high rotation speed. A nonmagnetic steel enclosure is needed to cover the PM material. The tensile press of PM can be reduced by pre-pressure applied to the outer surface of the PM through shrink-fitting into the enclosure. In this paper, the comprehensive optimization design of PM rotor structure is introduced with multiple constraints, such as deformation, stress and critical speed. The capacity of enclosure is the optimal goal. By finite element non-linear contact and optimization analysis, the optimized result for a high speed PM machine with rated speed of 60 000 rpm is presented.