Fall down and re-levitation dynamics of an electric rotor system with nonlinear AMB forces under base excitations: Modeling and experiment

The fall down and re-levitation dynamics of an eccentric electric rotor system under base excitations are investigated theoretically and experimentally. A universal unbalanced electromagnetic force model considering both the dynamic and static eccentricities is proposed. The coordinate system can remain unchanged and the direction of eccentricities can be characterized. The nonlinear suspension model for the AMB is derived and the scope of application is enlarged. Based on the unbalanced electromagnetic forces, nonlinear suspension forces and contact forces of touchdown, the dynamic models of electric rotor system and inner race are established, respectively. Furthermore, the re-levitation control is examined and a nonlinear PID re-levitation approach is adopted. Numerical simulations and experiments are conducted to investigate the regular, fall down and re-levitation dynamics for different eccentricities, rotating speeds and base excitations, etc. Results of experiments and numerical simulations are in perfect good agreement. Results and discussions indicate that the unbalanced electromagnetic model considering the amplitude and direction of various eccentricity cases is universal and can be smoothly applied in the analytical or numerical calculation. Moreover, the fall down state can be classified into bounce, friction and bounce as well as full rubbing, which is largely determined by the initial fall down speeds. The increasing rotating speeds exacerbate the fall down performances. The nonlinear PID re-levitation method behaves more effectively and reliably than traditional PID re-levitation approaches. The proposed method can withstand many common interferences such as sinusoidal acceleration, shock acceleration and random acceleration.