Research on the Bearingless Brushless DC Motor Structure with Like-Tangential Parallel-Magnetization Interpolar Magnetic Poles and Its Air-Gap Magnetic Field Analytical Calculation

This work focuses on the small Bearingless Brushless DC Motor (BL-BLDCM), to solve the problems, such as larger commutation torque ripple and difficult solution of air-gap magnetic field, a novel BL-BLDCM structure with like-tangential parallel-magnetization interpolar magnetic poles (LTPMIMPs) is proposed, which is abbreviated as BL-BLDCM-LTPMIMP in this work, and the analytical calculation model of its air-gap magnetic field has been investigated. First, inserting a like-tangential parallel magnetizing auxiliary magnetic pole between every two adjacent single-radial-magnetizing main poles, and forming several combination magnetic poles, each of which is composed of a radial-magnetizing main magnetic pole and two semi-auxiliary-magnetic-poles (with different magnetization directions) located on both sides. Then, by solving the Laplace equation and Poisson equation in every subdomain, and combining the relative permeability function, the analytical expressions of the air-gap magnetic fields for the BL-BLDCM-LTPMIMP was obtained. The armature reaction magnetic fields of the torque windings and suspension windings are also analyzed. Finally, through the finite element method (FEM), the correctness and computational accuracy of the analytical calculation model for the air-gap magnetic field is proven. Additionally, the comparison of electromagnetic characteristics with ordinary BL-BLDCM shows that the BL-BLDCM-LTPMIMP can not only effectively improve the amplitude and stability of electromagnetic torque on the basis of obtaining a shoulder-shrugged trapezoidal wave air-gap magnetic field but also has stable radial magnetic levitation force control characteristics.