Improvement of phase margin of controller for an electromagnetically borne rotor with large gyroscopic effect

The gyroscopic effect is proportional to the rotational speed and polar moment of the inertia of a rotor. This effect appears in a rotating machine borne by electromagnetic bearings due to high speed rotation and compactness of the rotor. Natural frequencies of the rotor system change depending upon the gyroscopic effect, which is proportional to the rotational speed. The natural frequency of a rotor at rest is separated into forward and backward natural frequencies as the rotational speed increases. The former increases with the speed and the latter decreases. The difference between them depends upon the gyroscopic effect. From the viewpoint of control engineering, this effect means the change of a control objector. Then, the phase margin of the controller must cover a frequency range where the rotor natural frequencies change. In this paper, some techniques are shown to improve the phase margin through by passing the actuator current, notch filter for rotor bending mode vibration, cross network based on the rotor whirl motion and so on.