Nonlinear Control Thoery And Its Application To Aircraft Antiskid Brake Systems

For modern aircraft, the antiskid braking system is one of the key airborne equipment and plays a very important role in safe takeoff and landing. While accidents and incidents involving aircraft overrun and loss of directional control due to antiskid braking system remain an important concern, the researches on the system, especially on application of the latest achivement of modern control theory to aircraft antiskid braking system, are not so satisfactory that it can insure safe ground handling operation under adverse conditions. There are many nonlinearities and uncertainties in aircraft braking system,espacially the maximum friction coefficient can vary in a certain range, and will affect the performance of system seriously. Therefor, it is meaningful to improve the performance of antiskid braking systems by means of parametric uncertainty nonlinear control theory, and it is the topic of this dissertation. Based on the review of progress in parametric uncertainty nonlinear system control theory, it is noticed that design methods based on feedback linearization are the main parts and the author proposes a robust controller design method for a nonlinear parametrization uncertain system satisfying feedback linearization and triangularity conditions,and a robust output tracking controller for a nonlinear parametrization uncertain system based on the identification of uncertain parameters. The latter,which is the first creative point,is the basis of robust controller design for aircraft antiskid braking system in this dissertation. Based on the analysis of mechanism of tire-runway friction force, the author analyzes the aircraft hydroplaning and its provision, measures the principles and performances of different types antiskid braking systems, the performance degrading and its solutions. The braking efficiency is a main performance index in aircraft antiskid braking systems, the author studies the relationship between control accuracy and braking efficiency, so that we may design antiskid braking systems by means of braking efficiency directly, and this is the second creative point. The author also studies the relationship between the maximum friction coefficient, optimum slip ratio, friction coefficent with locked wheels and three parameters in friction coefficient function of slip ratio, and three fit functions derived from experimental analysis, maximum friction coeffient, optimum slip ratio and friction coefficent v~ ith locked wheels, of aircraft speed. At last, the author proposes a quantitative relationship between tire-runway friction coefficient, aircraft speed and slip ratio, this is the third creative point. The author proposes a new parameter online identification method for nonlinear parameters in a common friction coefficient function of slip ratio. On the basis of a derived friction coefficient from dynamics equation of braked wheels and one step Taylor function between friction coefficient and variable value of the parameters to be estimated, we can calculate the estimated parameters This is the fourth creative point. By the use of controllers derived from feedback linearizable principle and output tracking method based on parameter identification, the author studiesthe perfOrmance of a certaln alrcraft antlskld braklng system under dlfferentkinds of runways, with or without landing parachute, and analyzes the factorsaffecting the system perfOrmance. Aircraft antiskid braking system can meetthe performance indexes by means of a fit weighting matrix in controllerdesign. It is shown that both...