Application of modern control and nonlinear estimation techniques

Control and nonlinear estimation techniques applied to optimal guidance of low thrust spacecraft, planetary soft landings, and feedback systems desig

Electromagnetic control of oil-film supported rotors using sparse measurements

An electromagnetic controller is applied to a flexible rotor supported by two oil-film bearings. The synchronous vibration is controlled by using a combined estimation and optimization algorithm. This requires no a priori knowledge of the system model. The effect of using a limited number of measurement sites on the controller performance is assessed. Optimum measurement sites are defined. The results of both computer simulations and experimental studies are presented. It is shown that the strategy developed by the authors can reduce the synchronous vibration to less than 10 percent of the uncontrolled response. The open-loop adaptive strategy can be applied to reduce the time required for in-situ tuning of magnetic controllers.</jats:p

Experiments on the transient performance of an adaptive multi-objective controller for rotating machinery

This paper describes an experimental assessment of the transient performance of a multi-objective adaptive approach to the control of flexible rotors. This is applicable to any arrangement of controllable bearings or actuators. In the case reported here, the rotor is supported by active magnetic bearings. The theory underlying the controller is outlined. The objectives include minimization of the forces transmitted to the base while restricting rotor vibrations to a user-defined limit. A third objective is to prevent rotor contact with the auxiliary bearings, which are used to protect the active elements. These objectives are met by a two-stage weighting strategy followed by the adaptive control of two parameters that automatically and continuously adjust the weightings of individual objective functions to satisfy user-defined performance criteria

Destabilization of forward rub in rotor magnetic bearing systems using actively controlled auxiliary bearings

During fault conditions, rotor displacements in magnetic bearing systems may potentially exceed safety/operating limits. Hence it is a common design feature to incorporate auxiliary bearings adjacent to the magnetic bearings for the prevention of rotor/stator contact. During fault conditions the rotor may come into contact with the auxiliary bearings, which may lead to continuous rub type orbit responses. In particular, forward rub responses may become persistent. This paper advances the methodology by considering an actively controlled auxiliary bearing system. An open-loop control strategy is adopted to provide auxiliary bearing displacements that destabilize established forward rub orbit responses. A theoretical approach is undertaken to identify auxiliary bearing motion limits at which forward rub responses become unstable. Experimental validation is then undertaken using a rotor/active magnetic bearing system with an actively controlled auxiliary bearing system under piezoelectric actuation. Two different operating speeds below the first bending mode of the rotor are considered and the applied harmonic displacements of the auxiliary bearing are shown to be effective in restoring contact free levitation.</jats:p

Wavelet coefficient characteristics during rotor/auxiliary bearing contact in active magnetic bearing systems

ABSTRACT Auxiliary bearings are present in active magnetic bearing systems to prevent rotor/stator contact. If rotor/bearing contact occurs, significant impact forces may arise. Furthermore, linear control strategies may become ineffective due to the non-linear dynamics introduced by the auxiliary bearing. Rotor/auxiliary bearing contact is therefore an important consideration for the continued safe operation of an active magnetic bearing system. This work utilizes the localized nature of wavelets coefficients in characterising rotor/bearing contact responses. An experimental approach is adopted using a flexible rotor/active magnetic bearing test rig. Different disturbances resulting in periodic rotor contact and rotor/bearing rub were applied using a single active magnetic bearing. Rotor displacements were measured and the radial component and associated wavelet coefficients identified from off-line data processing. Variations of the wavelet coefficients characteristics corresponding to the periodic contact and rotor/bearing rub are assessed. The choice of mother wavelet is seen to have only a small effect on wavelet coefficient values. Wavelet analysis is shown as a feasible method for identifying time-frequency characteristics of rotor/bearing contact. INTRODUCTION Active magnetic bearings are used in a range of applications with benefits for contact free/frictionless support, high rotational speeds, vacuum environments and active vibration control. In many applications active magnetic bearings are configured to op