Research On The Application Of Nonlinear Control Technology For Aircraft Anti-skid Braking System

With the further progress of aerotechnics,anti-skid braking system and control methods are also evolving for aircraft.The safety,stability and reliability requirements are getting more and more.The anti-skid braking system performance is particularly important for the safety with the requirements of complex environments,in order to ensure the aircraft efficient and safe implementation of the brake.The braking process involves a number of aspects such as aircraft landing,crosswind,runway condition and brake control strategy,which is an uncertain nonlinear process of vitally complex dynamics and kinematics.It has critical theoretical significance and high practical value by using uncertain nonlinear system control theory to design the anti-skid braking control law with the high efficiency,high reliability and high security.In this paper,the nonlinear characteristics are analyzed,and the nonlinear model of anti-skid braking system with systematic consideration is established.A deep study is made on the key issues of the breaking control,such as the tire / runway ground friction coefficient estimation,peak friction coefficient identification and the optimal slip rate nonlinear control.The major contributions summarized as follows:1)Consider the difficult of wheel/runaway friction coefficient acquisition in real time,a ground friction coefficient sliding mode observer is designed based on the aircraft anti-skid braking system nonlinear model.The feedback gain and observation gain selects to ensure the effective acquisition of the ground friction force,and obtain the wheel/runaway friction coefficient in real time.2)To deal with the slip ratio control challenge,the feedback linearization is proposed for the slip ratio with the analyzing the influence of nonlinearity and uncertainty on aircraft braking system.The linearized PID control law is designed to make up the chattering phenomenon caused by the differential item of the error.It improves the robustness and overcomes the shortcomings of the existing control method.3)Based on the complex nonlinearity of the peak frication coefficient and the influence of the runaway conditions and the speed,the linear parameterization algorithm for curve identification,which fitting empirical formula of slip-frication coefficient is proposed with the Burckhardt tire model.In this basis of beforehand research that estimation algorithm is designed by equality constrained least squares for the peak frication coefficient.The algorithm is employed to increase the robustness of the peak friction identification against initial errors and the accuracy,which lays the foundation for the optimal slip rate control.4)For the problems of the aircraft braking system,which include nonlinearity,uncertainty with parameter variation and optimal slip ratio control,the backstepping strategy is presented for the braking pressure control,and the adaptive second sliding mode control law is designed to achieve the tracking of the optimal slip ratio law.It overcomes the slip ratio limitation of the upper bound of the perturbation and the derivation of the sliding mode variable,and solves the chattering phenomena and switching gain.The design of the control law is simplified,while the control structure is not changed and facilitates the implementation.Finally,the thesis analyzes the results between simulation and inertia bench test with the same type of aircraft,which tokens under different runway conditions.The two kinds results consistent with each other and proved that the aircraft braking system model and braking control methods are reasonable and feasible.