Primary Resonance Analysis of Permanent Magnet Synchronous Motors Caused by Unbalanced Magnetic Pull

The dynamic behaviors of permanent magnetic synchronous motors considering unbalanced magnetic pull have been extensively investigated. However, the harmonics and cogging effects are ignored and the stator and the rotor are assumed to be smooth cylinders. In this research, an analytical expression of unbalanced magnetic pull considering harmonics and cogging effects is obtained. Based on the model, the motion equations of the rotor system are established. The natural frequency and frequency-response are analyzed by average method, and stability of periodic solution is investigated by Routh-Hurwitz criterion. The analysis indicates that the natural frequency is closely related to stator slot parameters. The frequency-response shows that the amplitude varies between the two static equilibrium points. Besides, when the ratio of slot width to stator slot pitch is close to the peak value, the amplitude tends to be increasing obviously. It is useful for the design of permanent magnet synchronous motors with high stability and low vibration.