Control and Nonlinear Compensation of a Rotor/Magnetic Bearing System Subject to Base Motion

In this paper a study is undertaken which compares the suitability of controllers for a magnetic bearing/rotor system in which motion of the system base can occur. It is demonstrated that controllers which have been selected for directly forced vibration control without consideration of this type of disturbance may give unacceptably poor performance when motion of the base occurs. A method is outlined for designing controllers to give optimal performance for combined base motion and direct rotor forcing disturbances. Controllers were implemented on a flexible rotor/magnetic bearing rig, the base of which was subjected to impulse inputs. The results obtained indicate that motion of the system base, when of sufficient magnitude, can drive the system into a state where magnetic bearing control force saturation occurs. To obtain improved performance a method of on-line compensation was used to linearise the control force characteristics. The results presented in this paper provide a foundation for the controller design of flexible rotor/magnetic bearing systems in applications that induce base motion. These would include transport environments, situations where the system is part of a larger vibratory structure, or in cases where seismic events can occur.