The analysis of high speed slotless permanent magnet brushless DC motor based on soft magnetic ferrite

Considering the characters of high permeability, high resistivity, low loss and low cost for soft magnetic ferrite in high-frequency alternating magnetic field, this paper proposes a novel high speed permanent-magnet motor based on soft magnetic ferrite. Soft magnetic ferrite ring is used for stator core, rare earth permanent magnet ring serves as the rotor poles, and the slotless configuration with long effective air gap is adopted. The size matching design between the stator magnetic ring and the permanent magnet magnetic ring can make them work in their best operating points respectively, and lower core loss and higher power density will be ensured in the motor. This paper describes an improved analytical model for analyzing the characters of air-gap magnetic field distribution and derives the expressions of phase winding induced electromotive force. The analytical results are compared with those of finite element method and the prototype test, which verify the accuracy of the analytical method is satisfactory, and provide a theoretical basis for the design of this type of motor.