Colloquia

Summary

In this master assignment a design for a rotor bearing system is proposed. It concerns a rigid rotor with a disk attached that has to rotate at 20,000 RPM in a near vacuum environment. Classical mechanical bearings would result in a contaminated environment because of particles created by wear as well as from lubricants. Because of this it is chosen to support the rotor with contactless active magnetic bearings.

Unbalance in the rotor system will result in synchronous forces in the bearings when the axis of rotation is fixed to the geometric centerline of the rotor. These forces may become too high and can also result in instability. By using a control strategy for the magnetic bearings that lets the rotor spin around its principal inertia axis, these unbalance forces are eliminated. The chosen control strategy utilizes a notch filter with phase shift to filter out the synchronous current. This leaves the synchronous vibration caused by the displacement stiffness of the bearings, which is compensated by an additional feedback controller. This strategy allows for exceptionally high rotational speeds while maintaining stability.

The time-continuous dynamics of the rotor have been modelled in order to predict the behavior of the system with a given unbalance. This model has been combined with a discretized controller. The controller can be used as a starting point for the software code in the actual setup to be realized in the future.