Abstract: Due to the asymmetric structure of air gap of the single-phase permanent magnet brushless DC motor, coupled with the inevitable deviation of the concentricity processing between the rotor and shaft, it will bring rich harmonic content to the air gap magnetic density and radial electromagnetic force. Aiming at the problem of 11~20-fold frequency noise in the single-phase external rotor refrigerator fan, first derives the radial electromagnetic force of the permanent magnet motor in the uneccentric and eccentric state, and points out the radial electromagnetic force order and frequency under eccentric state. Secondly, it analyzes the influence of gradual air gap on the air gap flux density of the motor, and the influence of different surface magnetic curves on the air gap flux density and back EMF harmonic content, and the influence of different surface magnetization schemes on the radial electromagnetic force under the moving eccentric state is analyzed. The simulation results show that reasonable adjustment of the magnetization method and weakening the peak magnetic peak can effectively reduce the amplitude of the radial electromagnetic force. Finally, it is verified through experiments that the flat-top wavetable magnetic scheme can significantly improve the noise problem. The research results provide a reference for the design of the outer-rotor permanent magnet motor.

Key words: Single-phase permanent magnet brushless DC motor, Rotor eccentricity, Vibration and noise, Magnetizing method, Outer-rotor motor