NASA Glenn Research Center (GRC) has developed a Fault-Tolerant Magnetic Bearing Suspension rig to enhance the safety of the bearing system for multiple component failures. A simple proportional-integral-derivative (PID) controller with no fault detection mechanisms was tested in a passive way where the initial bias current and control gains for all the eight heteropolar poles were not changed for the remaining active poles in the fault situations. The action of the integral term in the controller generated autonomous corrective actions for the pole failures to return the rotor to the set point (middle position) after the failure transient. The system stability and control of the rotor position were maintained over the entire speed range, where the rotor passes through the rigid body critical speeds and other rotor disturbances, provided that there was sufficient position stiffness and damping at low speeds. As far as the summation of force vectors of two attracting forces and rotor weight is zero, the passive fault tolerance was successfully demonstrated by using as few as two active poles out of the eight independent poles from each radial bearing (that is simply, 12 out of 16 poles dead). The rotor was spun without losing stability or desired position up to the rig’s maximum allowable speed of 20,000 rpm.

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