Abstract: To investigate the stability of rotor-active magnetic bearing (AMB) system, the nonlinear dynamic characteristics of the five-DOF AMB-rotor system is researched from the perspective of nonlinear multi-degree of freedom. With consideration of the cyclical impact of electromagnetic force, gravity and unbalanced force, a dynamics model of the five degree freedom AMB-rotor system is established. The five-DOF nonlinear differential equations are processed by using the basic principle of multi-scale complex number method using expansion of Taylor’s formula. The Poincare section maps and phase diagrams of the double periodic, quasi-periodic and chaotic motion are obtained and analyzed by software Matlab in complex number field. In the experiment, it is also discovered that with the increase of rotating speed, the axes orbit of rotor-AMB system becomes irregular instability state of motion from a regular steady state of motion. Numerical simulation and experimental results show that there are abundant nonlinear dynamics phenomena in AMB-rotor system. There exists the phenomenon of stable periodic motion, critical quasi-periodic motion and instable chaotic motion when system is under different parameter conditions.

Key words: Active magnetic bearing, Five-DOF, Nonlinear dynamics, Rotor system