Investigation of Electromagnetic Forces Acting on Rotor Considering Modulation Effect of Surface-Mounted Pole Structure

While the modulation effect of stator teeth on electromagnetic forces (EFs) acting on the stator surface has been extensively studied, EFs acting on the rotor with the corresponding effect considered remain largely unexplored. This article reveals that the surface-mounted magnet poles can act as modulators of EF harmonics, which indicates that high-order EF harmonics also contribute to low-order mode rotor vibration. To specifically explain the force modulation effect of magnets, this study introduces an intuitive masking function. Furthermore, an analytical procedure is developed to reidentify dominant field harmonic sources and EF harmonics of low-order modulated forces, with both field and force modulation effects considered. The field component contribution is analytically quantified by the amplitude-, force modulation-, and field modulation coefficients. Subsequently, the influence of the pole arc ratio and tooth-tip arc ratio is investigated for low-vibration design. The findings show that the contribution of a high-order EF harmonic to a certain modulated force can be comparable to that of a low-order EF harmonic. In addition, there exists an overlapping range of the above two design parameters to achieve low vibration and high torque. The analysis is validated by the finite element method and experiments.