Robust sampled-data control of hydraulic flight control actuators

In todays flight-by-wire systems the primary flight control surfaces of modern commercial and transport aircraft are driven by electro hydraulic linear actuators. Changing flight conditions as well as nonlinear actuator dynamics may be interpreted as parameter uncertainties of the linear actuator model. This demands a robust design for the controller. Here the parameter space design is used for the direct sampled-data controller synthesis. Therefore, a static output controller is choosen, the model discretized by approximation and the specifications represented by eigenvalue location. Simultaneous l-stabilisation allows a graphical controller selection. With realistic assumptions, the positioning system of control surfaces correspondes to conventional hydraulic actuation. The relevant uncertain parameters of the time-continuous linear model are the hydraulic damping and eigenfrequency. Avoiding a feedback for the servo valve and predesigning the position feedback gain due to the specified bandwidth, the velocity and acceleration feedback gain follow from direct pole region assignment. It follows that here only the velocity feedback gain is required. For the generation of the velocity signal a digital differential filter is applied. Simulation results in time- and frequency-domain shows the improvement by the choosen robust controller