A Sleeve-Free Interior Permanent Magnet High Speed Motor with Non-Uniform Airgap

The extra electromagnetic airgap thickness, high core losses and complicated rotor assembly are three crucial problems for the surface-mounted permanent magnet (SPM) motors with sleeve-protected rotor in high speed (HS) fields. In this paper, a novel sleeve-free interior permanent magnet (IPM) HS motor with non-uniform airgap is proposed on account of high torque density, low losses and easy of manufacture. Firstly, the features and advantages of the proposed rotor structure are detailed illustrated in term of mechanical strength, dynamic stability, core losses and material properties. Thereafter, in order to take fully advantage of the proposed structure, the optimization of the rotor non-uniform outer periphery and the shaft diameter is carried out by using finite element analysis (FEA) method. Finally, the comprehensive electromagnetic and mechanical performance of the proposed motor are evaluated and compared with a uniform airgap IPM motor and a sleeve-protected SPM motor in HS operation. And it is concluded that the proposed sleeve free non-uniform airgap IPM motor presents prominent advantages in motor losses, mechanical strength, dynamic stability and manufacture.