VIBRATION CONTROL OF A FLEXIBLE ROTOR MAGNETIC BEARING SYSTEM SUBJECTTO DIRECT FORCING AND BASE MOTION DISTURBANCES

During operation, a rotor/magnetic bearing system may be subject to va rious sources of vibration, either directly applied to the rotor or tr ansmitted through the bearings owing to base motion. This paper consid ers controller designs that are capable of attenuating vibration arisi ng from either source. It advances the current state of research in th e area since other controller designs have considered only the direct forcing case. If base motion is not considered in the design of the co ntroller then this disturbance may cause the bearing clearance limits to be reached. Controller design is formulated as an H-infinity optimi zation problem, with mixed design objectives. A new controller is deri ved that can simultaneously reduce vibration and minimize the effect o f base motion on relative rotor to bearing displacement. Account is ta ken of the fact that the bearings can apply only limited control force . The design study was complemented by a programme of experimental wor k. The base of a rig was subjected to impulse inputs and the results s how the effectiveness of the new controller design. It is demonstrated that proportional, integral and derivative (PID) controllers, or cont rollers designed for unbalance vibration attenuation only, may result in rotor contact with retainer bushes, while the new controller may pr event contact. The potential now exists for continuing safe operation of flexible rotor/magnetic bearing systems such as compressors, gas tu rbines, generators, etc., in transport applications, during seismic ev ents or in environments with expected base input disturbances.