Pid + rule - based variable structure control of active magnetic bearings for high speed rigid rotors

In this study, a contactless magnetic radial shaft bearing control algorithm has been developed for high speed five degrees of freedom rigid rotors with external asymmetrical loads. The developed control algorithm keeps the rotor on rotating through its geometric axis while keeping on the radial air gap in stator housing to be constant at maximum value in every direction to compensate the mass imbalance due to asymmetrical loading. In this method, the radial air gap lengths along the direct and quadrature axis of bearings are measured and then, from these measurements, the radial position errors and the angular position displacements around the direct and quadrature axes on the radial plane through the stator geometric centre are estimated. The radial position errors and the estimated angular displacements differentiated by using derivative filters to get the relevant speed errors and the sliding surfaces to switch the H-infinity optimal PID controllers on the position errors, thus, on the basis of the dynamical and hierarchical rules by the translational and rotational sliding surfaces, the continuous control signals from the PID controllers and the discontinuous control signals from the rotational PID plus PI type sliding mode controllers are combined to form the inputs to the linearizing external feedback blocks producing the reference currents to the chopper-controlled current sources to supply the desired currents through the electromagnet coils