Noncolocation Effects on Rigid Body Rotordynamics of Rotors on AMB

The effect of sensor-actuator non-colocation on the behaviour of machines running on acive magnetic bearings is studied under the assumptions that the rotor behaves as a rigid body, the controller is an ideal decentralized proportional-derivative one, the behaviour of the bearings can be linearized and the whole machine is axially symmetrical. The possi- ble presence of an instability range, which in some cases can extend down to the zero-speed condition, is demonstrated. The effect of damping on the insta- bility range is studied, showing that it is stabilizing and that, with damping high enough, it is possible to achieve stable running in the whole working range. A simple centralized controller which cures the con- sequences of non-colocation is shown to exist and its gains are computed. The paper includes also an ex- ample related to an actual machine showing strong non-colocation effects.