Vibration control and stability analysis of rotor-shaft system with electromagnetic exciters

Reduction of rotor vibration is very important for safe and efficient functioning of all rotating machines. This paper proposes an active vibration control scheme for controlling transverse vibration of a rotor shaft due to unbalance and presents a theoretical study. The technique uses electromagnetic exciters mounted on the stator at a plane, in general away from the conventional support locations, around the rotor shaft for applying suitable force of actuation over an air gap to control transverse vibration. Electromagnets used for vibration control do not levitate the rotor and facilitate the bearing action, which is provided by conventional bearings. Suitable force of actuation is achieved by varying the control current in the exciters depending upon a proportional and derivative control law applied to the displacement of the rotor section fed back by pick-ups with respect to the non-rotating position of the section taken as the reference. Thus the technique provides control force over an air gap and hence is free from the difficulties of maintenance, wear and tear and power loss. Preliminary theoretical simulation using linearized expression of electromagnetic force and the accompanying example show good reduction in transverse response amplitude, postponement of instability caused by viscous form of rotor internal damping as well as great reduction of support forces.