Acceleration feedforward control for active magnetic bearing systems excited by ground motion

When a magnetic bearing-rotor system is excited by ground motion, the rotor may come into contact with the stator because of its low stiffness and the system may suffer heavy damage. Although magnetic bearings are equipped with touchdown bearings for emergencies such as earthquakes, it is desirable to design a controller which can restrain the foundation-excited response of a rotor within the designed gap. In proportional-integral-derivative (PID) control, gains have to be adjusted for many purposes and tradeoffs in control performance are inevitable. The paper thus presents acceleration feedforward control methods designed to reduce the ground-motion response of the active magnetic bearing system without sacrificing other control performances. When this acceleration feedforward control is applied to an experimental apparatus, the response of a rotor to ground motion is reduced to about half that by PID control alone. Furthermore, this suppression of the response is carried out with less control current