Analyses of electromagnetic forces of concentrated winding permanent magnet brushless motors with rotor eccentricity

Analyses of harmonic electromagnetic forces have been a major factor for the noise reduction of concentrated winding permanent magnet brushless motors with rotor eccentricity. In this paper, the distributions of electromagnetic forces of the motors with rotor eccentricity are evaluated by measurement using search coils, and finite element analysis (FEA). The spatial distributions of the electromagnetic forces, and the time variation of the electromagnetic forces by using the short-time Fourier transform (STFT) are visualized. The harmonic component of the forces caused by the rotor eccentricity is specified. A rotor structure is designed to reduce the magnitude of the harmonic component, and the effect is confirmed by FEA.