-This paper proposes a novel Lorenz-force-type bearingless motor with single-axis actively positioned functionality. The novel motor consists of two slotless surface-mounted permanent magnet (SPM) motors, which have six skewed coils for each motor to constitute 3-phase windings and are in tandem along axial direction so as to achieve actively regulated axial motion. Additionally, two repulsive permanent magnet bearings (RPMBs) are used to passively stabilize radial-and tilting movements of the rotor. The slotless stator iron is employed for arrangement of the skewed coils in toroidal form. Compared with state-of-the-art single-axis actively controlled bearingless motors utilizing field weakening or strengthening effect of d-axis current to regulate axial movement, perhaps suffering irreversible demagnetization of permanent magnets especially at the time of start-up, the merit of this proposed motor is beneficial to prevent the demagnetization risk of permanent magnets. To verify the novel concept, firstly, theoretical analysis is carried out for modeling back electromagnetic force (back-EMF), axial force, drive torque. Followed by the analytical model, a detailed design process by integration of analytical method and finite element analysis (FEA) for the structural parameters are revealed. At last, 3-D FEA is performed to validate the correctness of analytical model, design process as well as to evaluate the performance of proposed motor.

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.