Modelling and control of a hydraulic servo system

This thesis examines the modelling and control of a hydraulic servo system. Both a theoratical and a practical approach are discussed. The used set-up consists of an one DOF hydraulic system with an electronically controlled servo valve. A nonlinear parametric model of the system, several fitted linear black box models as well as a LPV model combining these fits are determined. The models are verified with the use of experimental data. Combining position and pressure feedback, classical hydraulic controllers, H∞ controllers and a LPV controller are designed to control the position of the rod. The design of the controllers takes into account several aspects of the system’s dynamics like the damping effect of pressure feedback and the nonlinear characteristics dependent on the position of the rod. The controllers are implemented using an analogue control board as well as a discrete dSpace system. In discretisation of the control strategies for implementation on a discrete dSpace system, a new algorithm is derived for LPV structures. Simulations and experimental results indicate the benefits of a variable controller over a classical controller, but show the limitations to this strategy as well. This reports concludes with the suggestion that the next step in researching servo hydraulic actuators, is the combination of hydraulic servo control and mimo systems. For this purpose, a two DOF hydraulic system with varying dynamic interaction between the DOF’s is designed and built. To facilitate the design of a mimo controller, MCDesign is developed, a tool for mimo controller design based on measurements data from a mimo system.