Analysis of Influence of the Inner Diameter of the Permanent Magnet on Rotor Stress and Critical Speed for the High Speed Permanent Magnet Motor

Abstract

While the rotor of a high-speed permanent magnet motor runs at high speed, it is difficult for the permanent magnet to bear the huge tensile stress which caused by centrifugal force. In addition, the rotor is also prone to vibration and even bending deformation due to resonance. Therefore, the strength and critical speed of the rotor must be analyzed and checked. In this paper, because of the slim characteristic of high speed permanent magnet rotors, the displacement and stress fields of a 150 kW, 30 000 r/min surface mounted high speed permanent magnet motor rotor are deduced based on the theory of the thick-walled cylinder. The finite element method is used to verify the correctness of the analytical calculation. Based on the deduced analytical formulas, the influences of the inner diameter of the permanent magnet and the sleeve material on the rotor stress are analyzed. At the same time, the finite element method is used to calculate the critical speed of the rotor and analysis the influences of the inner diameter of the permanent magnet and the sleeve material on the critical speed of the rotor shaft system. A basis for the design of the high speed permanent magnet motor rotor is given.