Mechanical-electromagnetic coupling elastic vibration instability of symmetrical three-phase external rotor induction motor

Abstract

The work investigates the elastic vibration instability induced by rotating electromagnetic load in symmetrical three-phase external rotor induction motor with compliant rotor and stator. The investigation is based on a mechanical-electromagnetic coupling dual-ring model undergoing flexural and extensional deformations. The model is established in a field-synchronous coordinates such that the time variance of electromagnetic load can be eliminated. The dependence of electromagnetic load on pole pair count and wavenumber is classified into typical cases. The eigenvalues are calculated by simple vibration theory such that unstable behaviors can be accurately estimated. The estimation is independent of weak-parametric source assumption. For verification purpose, a time-variant model is constructed in the inertial frame, based on which typical cases of the time-variant electromagnetic load are classified in terms of the pole pair count and wavenumber. Numerical calculations are performed by using Floquet theory, and transition curves between stable and unstable regions are identified. The results in field-synchronous and inertial frames are well compared with each other.