Regelung eines elektropneumatischen Bleed-Air Systems

Abstract

Conventional passenger airplanes use bleed-air to keep the cabin well pressurized and tempered for comfortable and safe travel conditions. The high pressurized bleed-air from the aircraft engine therefore has to be expanded and controlled to a constant mass flow. The bleed-air system, doing this job, consists of three valves connected through pipes. The state of art is PI control of the valves, applied in flight tests. Experience shows that in practice limit cycles occur, downgrading performance. The challenge of control consists in the little control authority, the high friction in the valves causing stick-slip action and the coupling of three valves. Three approaches are followed for developing new control strategies. The first one provides a centralized controller for all valves. Second applies different stiction compensation techniques handling the high friction level and last tries to decouple the valves through a feedforward control at the second valve. The three concepts are combined to nine controller variations. For comparing the approaches and their interdependency, each of the resulting controllers is adjusted to the bleed-air system model using global optimization. Thereby movement and integrated absolute error are rated. Effectiveness and robustness of the approaches are discussed. It is showed, that feedforward control and I-Gain Tuning account for significant control improvement. Finally, suggestions for improving the quality of model-based developing for bleed-air systems are derived from the experiments.