Research On Sliding Mode Control Method Of Aircraft Electric Anti-skid Braking System

With the development of aviation technology,the aircraft braking control system is also constantly updated iteratively,which puts forward higher requirements for safety,reliability and stability.Aircraft antiskid braking has the typical characteristics of strong nonlinearity,strong coupling and time-varying parameters,and the disturbance of the runway environment is easy to adversely affect the ground roll performance of the aircraft.Therefore,the development of aircraft anti-skid braking control law is a complex system engineering,and it is also regarded as the core key technology by the braking system suppliers of various countries.In this thesis,some key problems such as estimation of aircraft speed and wheel angular velocity state information,complex nonlinear disturbance observation and real-time updated optimal slip rate tracking control are deeply studied.Based on sliding mode control theory,the anti-skid braking algorithm with tracking optimal slip rate as the control target is designed by combining Extended Kalman Filter,nonlinear disturbance observer,dynamic surface control and feedback linearization techniques.Its main research contents and contributions are as follows:(1)The composition and working principle of aircraft electric braking system are analyzed deeply,and mathematical models of key components of the braking system are established,including aircraft body dynamics,single main wheel braking dynamics,tire-runway friction and electromechanical actuator model,etc.According to the relationship among various component models,a third-order closed-loop feedback system with slip rate loop,speed loop and current loop is formed.Aiming at the problem that it is difficult to obtain accurate information of aircraft speed and wheel angular velocity during braking,an Extended Kalman Filter is designed to predict the state information.(2)Combining the advantages of sliding mode variable structure control,a finite-time convergent sliding mode control based on dynamic surface technology is designed,and nonlinear disturbance observer is used for online estimation and disturbance compensation to suppress the influence of uncertain disturbance on system stability.In addition,because the finitetime convergence control depends heavily on the initial value of the system,the fixed-time convergence sliding mode control method is studied,in which the convergence time does not depend on the initial value of the system.The stability and convergence time of the proposed sliding mode control law with finite/fixed time convergence are proved by Lyapunov theory.At the same time,numerical simulation experiments show that the two control methods have good control performance,and the nonlinear disturbance observer can accurately estimate the uncertain disturbance,which improves the robustness of the system.(3)Considering that the finite/fixed time convergence sliding mode control method still has the defects of long rise time and adjustment time,and large tracking error at low speed.A recursive fast terminal sliding mode control method based on feedback linearization and nonlinear disturbance observer is proposed.First,by performing feedback linearization on the high-order nonlinear braking system,it is rewritten into a strict linear standard feedback form.Secondly,an improved nonlinear disturbance observer is designed to estimate disturbances online,which has the ability to observe high-order differential disturbances and is used as a compensation part in the control law.Then,by constructing a fast terminal sliding mode controller with a recursive structure to track the real-time changing optimal slip rate and establish the stability condition,the limited-time fast stabilization of the aircraft electric anti-skid braking system is realized and the main wheel locking slip is effectively suppressed..Finally,through numerical simulation under different runway conditions,it is verified that the control method can effectively improve the braking efficiency.There are 32 figures,6 tables,and 105 citations in this thesis.