Modeling and robust control design for aircraft brake hydraulics

This article describes the modeling of an electrohydraulic pressure servo v alve and brake hydraulic system, and the design of an inner-loop controller which can be used with independent antiskid or autobrake controllers. The effects of the connecting lines on stability and performance are explicitly taken into account in control design by using the analytical solutions to two-dimensional viscous compressible model of fluid motion in the pipe. The modal approximation technique is used in the simulations. In order to faci litate central design, singular perturbation analysis is employed to reduce the order of the model in a systematic fashion. Combining partial feedback linearization and linear H-infinity control, guaranteed stability robustne ss against oil parameter variations and component wear is achieved. Both th e model reduction and control design are described in some detail for the s ake of illustrating the concepts. The closed-loop response is almost linear , fast, sufficiently damped, consistent over the whole operating range and the asymmetry between filling and dumping is significantly reduced. Computa tional requirements are modest and with careful coding, the inner-loop cont roller can be incorporated into existing antiskid controllers.