Control of magnetic bearing using the observer for unbalance

AbstractAn unbalance on a rotor causes whirling motions of the rotor and alternating forces of the bearings in rotating machines. The authors have shown a magnetic bearing control system in which an unbalanced rotor can be suspended without whirling. The concept of designing the control system involved an observer estimating the effects of unbalance and then cancelling using the electromagnetic forces of the bearing.With the control method applied, the position of the rotor can be maintained at the desired position with high precision. However, it is suitable for some machines to minimize the variation of exciting currents or vibratory force transmitted to the base through the bearing.This paper presents control methods that can eliminate stationary alternating components from exciting currents or electromagnetic forces by using the output of the observer.Another control method is presented in which feedback of the estimated signals of the displacements of the principal axis occurs; such signals are obtained by compensating synchronous observatory disturbances by use of the output of the observer. It is shown that the proposed three control methods are equivalent when unbalance sti