Vibration Instability of a Rotor in Axial-Field Permanent Magnet Motors with a Foundation Movement

This paper investigates the effects of a foundation movement on the vibration instability of axial-field permanent magnet motors (AFPMM). Different from previous studies focusing on the effects of the rotor’s rotation on its vibration instability, this paper introduces a revolution around a space axis as the foundation movement and investigates its effect on the vibration characteristics of the rotor. For an annular rotor with this foundation movement and a rotation around an axis passing through its own geometrical center, a dynamic model is established in this paper. Magnet-field-synchronous frame is introduced to describe the out-of-plane displacement. Hamilton’s principle and Galerkin method are involved to obtain dynamic mode. Closed-form expressions of eigenvalues and the boundaries of flutter and divergent instabilities are determined. The analytical results claim that the instabilities can be suppressed. Particularly, the divergent instabilities can even be eliminated by adjusting combinations of parameters. To verify the results, the stability analyses and numerical calculations regarding the revolution are given for a sample AFPMM revolving around a space axis at different speeds. Based on these analytical boundaries, the unstable regions of a sample motor with different parameter combinations are plotted in terms of foundation movement, which can be used to suppress the vibration instabilities with the design of parameters such as rotation speed, web thickness, magnetization thickness, air-gap length and remanence. Six states of instabilities are summarized as a guidance to determine the range of the stable operation of the motor.