Unbalance compensation in a rotor-bearing system by dynamic stiffness control and acceleration scheduling

This work deals with the application of an active unbalance compensation scheme for a rotor-bearing system by simultaneously using two control strategies, consisting in the synthesis of a dynamic stiffness controller and the acceleration scheduling for the rotor speed. The rotor-bearing system consists of an asymmetrical Jeffcott-like rotor system with a servomechanism to position a sliding bearing support such that the rotor lateral dynamics can be modified by controlling the effective rotor length and, as a consequence, the natural frequencies can be arbitrarily shifted into a small range, where the resonance can be passed and attenuated during typical run-up or coast-down operations. The system is modelled by a 4-DOF nonlinear system dynamics with two indirect control inputs, that is, the translational force applied to the sliding bearing and the torque in the rotor speed dynamics. The dynamic stiffness control is performed by adding a servomechanism based on a cd motor and a ball-screw to locate in proper positions the movable bearing support, by applying a fast and robust PD feedback control scheme, parameterized and monitored in terms of the actual rotor speed. The rotor speed dynamics is controlled to asymptotically track a smooth speed profile, which can be manipulated to reduce the overall unbalance response when the rotor is forced to pass over the first critical speeds. The overall unbalance response in the rotor-bearing system can be reduced up to 42.5% with respect to the open-loop response, which is validated with experimental results on a testbed designed and constructed for this purpose.