The use of canned rotors in high speed permanent magnet machines

The design of high speed permanent magnet motors involves taking into account conflicting requirements from the point of view of electromagnetic and mechanical design. The authors focus on a particular technique to achieve high torque to magnet volume ratio while providing an adequate mechanical strength for the rotor. For this purpose the use of a can, which may consist of magnetic or nonmagnetic material, to contain the rotor is proposed. The authors present the results of computational and experimental investigations on the use of a solid steel can and its effect on the performance of motors having high energy magnets. Accurate modelling of a particular design, obtained using the 2-D finite element software package MOTOR-CAD, is also given. The results obtained by computation show good agreement with those obtained experimentally