Modeling and robust control design for aircraft brake hydraulics

This article describes the modeling of an electrohydraulic pressure servo valve and brake hydraulic system, and the design of an inner-loop controller which can be used with independent anti-skid or auto-brake controllers. The effects of the connecting lines on stability and performance are explicitly taken into account in the control design by using the analytical solutions to 2D viscous compressible model of fluid motion in the pipe. The modal approximation technique is used in the simulations. In order to facilitate control design, singular perturbation analysis is employed to reduce the order of the model in a systematic fashion. Combining partial feedback linearization and linear H_∞ control, guaranteed stability robustness against oil parameter variations and component wear is achieved. Both the model reduction and control design are described in some detail. Computational requirements are modest and with careful coding, the inner-loop controller can be incorporated into existing anti-skid controllers