Research On Sliding Mode Nonlinear Flight Control For Diamond Wing Tilt Rotor UAV

The special structure design of tilt-rotor aircraft makes it have the vertical takeoff and landing capability of helicopter,and it also has the advantages of fast speed,long range and large payload.Compared with the conventionally arranged aircraft,the diamond wing layout aircraft has the advantages of high structural rigidity of the aircraft wing,small bending deformation of the front wing,low strength of the front wing tip vortex,and high operational efficiency of each rudder surface.In this paper,the flight control of tilt-rotor UAV with diamond wing configuration is studied.The diamond-wing tilt-rotor UAV is a complex controlled object.It has three modes of vertical takeoff and landing,tilt-transition flight and fixed-wing flight.It can switch different flight modes according to the need of mission.Because of its many flight modes,strong coupling of control channels and multi-input and multi-output characteristics,flight control system is needed to ensure UAV has good flying quality.Aiming at this problem,the attitude control of diamond-wing tilt-rotor UAV with complex disturbances is studied in this paper,which is based on traditional sliding mode variable structure control,combined with inversion control technology,ADRC technology,fractional calculus theory,anti-saturation control technology,neural network control technology,adaptive control technology and other advanced control methods.The contents are as follows:1.Mathematical models of aerodynamic forces and moments of components of diamond-wing tilt-rotor UAV and a six degree of freedom nonlinear dynamic model with complex disturbances are established.2.A novel logarithmic global fast non-singular terminal sliding mode controller is proposed for attitude control of diamond-wing tilt-rotor UAV in vertical takeoff and landing mode with modeling uncertainties and external disturbances.Firstly,in order to accelerate convergence to equilibrium state and avoid singularity,a new logarithmic form of global fast nonsingular terminal sliding surface is proposed.Secondly,in order to improve the shortcomings of traditional approaching law,such as serious chattering and long convergence time,a new fast reaching law with second-order sliding model is proposed based on the traditional approaching law.The sliding mode disturbance observer is used to estimate the complex disturbances in the system and compensate the controller to suppress the influence of external disturbances and uncertainties.Aiming at the attitude control problem of tilting-rotor UAV with diamond-wing configuration with actuator faults and external disturbances,the uncertainties and unknown external disturbances of the system and actuator faults are integrated into the combined disturbances,radial basis function neural network is used for approximation.Combined with the inversion control technique and the new logarithm non-singular global fast terminal sliding mode technique,a robust fault-tolerant inversion terminal sliding mode attitude control method is proposed.3.Aiming at the attitude control problem of tilt-transition flight mode of tilt-rotor UAV with diamond-wing configuration,the tilt-transition mode is divided into two stages and the attitude controller is designed.Combining with fractional calculus theory,the sliding mode surface of fractional calculus is designed to reduce the control overshoot of traditional integral calculus sliding mode surface.The uncertain non-linear function of the system is approximated by RBF neural network,and the weights of the neural network are adjusted on-line adaptively with adaptive theory.According to control characteristics of the second phase tilt-rotor UAV's tilt transition flight mode nacelle,the non-linear dynamic model of tilt transition nacelle of UAV with wind field parameters is established.Aiming at the influence of composite disturbance such as wind disturbance on the attitude tracking control of UAV,an adaptive fractional calculus sliding mode control scheme based on RBF neural network is designed.The numerical simulation demonstrates the effectiveness of the proposed control strategy.4.Aiming at the attitude control problem of fixed-wing flight mode of diamond-wing tilt-rotor UAV,a robust inverse sliding mode control strategy with actuator output nonlinearity is proposed.When the UAV actuator output is non-linear,the performance of the UAV attitude control system will decline.In order to ensure the stability of the control system,an auxiliary system is constructed to compensate the controller dynamically,thereby eliminating or reducing the influence of the non-linear control input on the controlled system.In the case of complex disturbance and actuator output nonlinearity,a robust constrained inversion sliding mode control method for fixed-wing attitude of tilt-rotor UAV with diamond-wing configuration based on auxiliary system is designed by combining inversion control technology and disturbance observer technology.In addition,considering actuator fault,a robust fault-tolerant inverse sliding mode controller is designed based on sliding mode disturbance observer technology.The simulation results show that the proposed control algorithm has good tracking performance.5.Aiming at the longitudinal trajectory control problem of fixed-wing autonomous landing of tilt-rotor UAV with diamond wing configuration,the autonomous landing trajectory control system of UAV is divided into five control loops: airspeed,longitudinal trajectory,titl angle,angle of attack and pitch angular velocity.Considering the transient and steady-state performance requirements of the closed-loop system,the preset performance method is introduced into the UAV airspeed control subsystem,and the preset performance equivalent error model of the airspeed control subsystem is established.Nonlinear fal function and hyperbolic cosine function are introduced into the design of the new reaching law to improve the convergence speed of the system state,and chattering is effectively suppressed.Combining sliding mode control,adaptive control theory and ADRC technology,an adaptive fractional-order calculus sliding mode autonomous landing longitudinal trajectory control method for fixed-wing flight mode of diamond-wing tilt-rotor UAV is proposed.