Analysis and Reduction of Cogging Torque of Permanent Magnet Synchronous Wind Generators Based on the Magnetic Field Modulation Mechanism

In this paper, a magnetic field modulation model considering the influence of phase angles is established for the analysis and weakening of the cogging torque of the permanent magnet synchronous wind generations. Compared with the existing analytical model, the modulation effect of the magnetic field harmonics and phase angle on the cogging torque components is analyzed in the new model. Firstly, flux density model with phase angle characteristics is derived, and the relationship of the cogging torque and magnetic field harmonic is analyzed using energy method. Then, based on the magnetic modulation mechanism, the impact of the phase angle and magnetic field harmonics on the coupling relationship among cogging torque components is analyzed. All cogging torque components are classified as a combination of multiple positive and negative harmonic components, and the contribution characteristics of the components are determined by the harmonic combination and phase angle characteristics. Based on the finite element model (FEM), the magnetic field modulation model of the cogging torque is proved. On the basis of the conclusions obtained, it is further explained that the suppression mechanism of rotor-step skewing is a mutual complementary effect of the positive components and negative cogging components, and the main harmonic is effectively offset by selecting the seasonable of segment number and skewed angle of rotor. Finally, in order to verify the validity of the analysis method, the no-load line back EMF and cogging torque of optimized prototype is tested, and the experimental results agree well with the FEM results.