Evaluation of modern control system design techniques for a multivariable electro-hydraulic system.

An experimental apparatus has been developed with the object of providing a test plant, based on commercially available electro-hydraulic components, for the investigation of multivariable control system design methodologies. A mathematical model has been produced for this experimental plant and a preliminary analysis of the plant carried out.A selection of controller design techniques has been investigated. Designs have been produced for two state feedback controllers in which the feedback coefficients were based on LQR theory, one of which used a full order estimator based on a Kalman Filter, the other using a reduced order observer whose poles were chosen arbitrarily. In addition, forward path compensators have been developed using the Characteristic Locus and the Hinfinity/Mixed Sensitivity methods. These controller designs were based on computations and simulations utilising Matlab and a selection of its control engineering toolboxes and Simulink. The completed designs were implemented in digital form and tested on the actual plant.A series of tests were carried out to assess the robustness of the various controllers in the presence of plant uncertainty. The physical plant was modified and the controllers based on the nominal plant model used in conjunction with this modified plant. As a design technique which enabled robustness issues to be addressed explicitly, the Hinfinity approach was used to improve the robustness of the original Hinfinity controller.