Comparison of magnetic forces for IPM and SPM motor with rotor eccentricity

The permanent magnet motor is often the most important element in many precision rotor applications and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper investigates radial force density and magnetic unbalanced force for IPM and SPM motors when rotor eccentricity exists. For the magnetic field analysis, a finite element method is used to account for the magnetic saturation and rotor eccentricity. The radial force density and magnetic unbalanced force are analyzed by Maxwell stress tensor and discrete Fourier transform. An IPM BLDC motor, mostly chosen to realize high speed operation, is significantly affected by rotor eccentricity due to magnetic saturation.