Study on the rotordynamics of a high-speed motor supported by air foil bearings

In order to adapt to the high speed of a high-speed permanent magnet synchronous motor (HSPMSM) used in hydrogen fuel cells, air foil bearings are applied to support the motor rotor. However, the stability of the motor rotor system supported by air foil bearings is relatively complex. In this article, the Castigliano’s second theorem and the theory of small deflection elastic thin plates are used to establish a deformation model of air foil bearings. Based on the generalized Reynolds equation, the stiffness and damping of the air foil bearings are calculated using perturbation methods and finite difference methods as the support model for the motor rotor. Subsequently, the transfer matrix of a typical disc-shaft unit is analyzed and obtained by using the transfer matrix method. On this basis, combined with Riccati transform, the natural frequencies and critical speeds of the motor rotor system in the spatial domain are calculated using MATLAB. And the unbalanced magnetic pull (UMP) is calculated by Maxwell stress tensor method, which is equivalent to the unbalanced mass and is applied to the disc it acts on to ascertain the unbalanced response, forming a theoretical model for calculating the dynamic performance of high-speed motor rotors. Then, the accuracy of the constructed model is verified by comparing the experimental results with a literature. Based on the estalished model, the effects of structural parameters and operating conditions on motor rotordynamics are studied, and the responses of the motor rotor system to unbalanced mass and unbalanced magnetic tension are compared. It is found that the critical speeds of the motor rotor system increase with the increase of the dynamic viscosity of air, and the motor can operate stably under the influence of the maximum UMP.