Stabilization of a Magnetically Levitated Rotor in the Case of a Defective Radial Actuator

This article describes an operation mode for the stabilization of a 5-DOF active magnetic bearing system in the case of a damaged radial actuator. The proposed method has the task to stabilize the underactuated rotor to ensure a safe deceleration. The resulting underactuated system is not reachable for the admissible angular velocity range. Thus, the rotor could be destabilized for some operating points. However, for a real system with a nonideal isotropic magnetic behavior, the system is reachable for all angular velocities. For the stabilization of the underactuated system, PID controllers are used. The parameters of the PID controllers are calculated using the linear quadratic regulator method. This simple realization of the controllers implies a short computing time. To show the stability and the robustness of the designed controllers, different root loci are visualized. The proposed operating mode is able to prevent the safety bearings from wear and damage in the case of a defective magnetic actuator. Finally, the underactuated operation mode is experimentally validated on a turbomolecular pump, where the center of gravity is not located between the magnetic actuators.