Mathematical Modeling of Rotor Dynamics in High-Speed Electric Motors for Aerospace Applications

Abstract

No aerospace system can function without high speed electric motors, which are compact form factor, high power density and very high dynamic response. These motors are operating at rotational speed of more than 50,000 rpm, while they are subjected to complicated dynamic phenomena, leading to structural integrity, low level of vibration and stable long term operation. Accurate modelling of the rotor dynamics in the high speed regime where gyroscopic precession, rotor stator electromagnetic interaction, bearing anisotropy and structural damping characteristics are present is a critical factor towards reliable motor operation. A comprehensive mathematical modeling framework for the rotor dynamics analysis especially in aerospace grade high speed electric motors is developed in this study. The modeling approach is based on Lagrangian mechanics, is distributed mass and stiffness, anisotropic bearing supports, and gyroscopic coupling effects. Discretization and numerical solutions of these resulting nonlinear coupled differential equations in time domain and frequency domain are performed. Comparisons are made to finite element simulation performed in COMSOL Multiphysics and experimental data from a 120 kW aerospace prototype motor running above 60,000 rpm at critical speed for critical speed identification, mode shape visualization, and damping behavior respectively. The dynamic response characteristics, vibrational modes, and stability thresholds, and these vary widely as functions of the design parameters, are predicted with fidelity. This study offers insights to be used towards improvement in the rotor design optimization, material selection and bearing configurations to help advance the next generation of more robust, efficient, and lightweight electric propulsion systems of the aerospace.