State/Parameter Estimation And Hierarchical Sliding Mode Control For Flexible Hypersonic Vehicles

The hypersonic vehicle represented by Advanced Hypersonic Weapon(AHW)of the United States has the potential to change the future wars,so it is an important development direction of vehicle.In order to meet the requirements of high speed and large range,hypersonic vehicles have larger larger aspect ratio and less structure weight,resulting in lower natural frequencies of elastic modes,which are close to the natural frequency of rigid mode.As a result,the coupling effect between elastic modes and rigid mode can not be ignored,and the elastic vibration characteristics need to be considered.Therefore,it is of great significance to study the dynamic modeling and control methods of flexible hypersonic vehicle.Concerned with the problem that the control system is degraded by the sensor affected by elastic vibration,this dissertation studies dynamic modeling,dynamic characteristics analysis,joint state/parameter estimation and attitude control methods for flexible hypersonic vehicles.The major contents of this dissertation are consisted in the following parts.Firstly,the dynamic modeling of the flexible hypersonic vehicle is studied.By introducing the transient coordinate,the quasi-velocity problem in the quasicoordinate system is overcome,and the decoupling of the motion of the center of mass with the attitude motion and the elastic vibration is accomplished.The dynamic equation is derived by using the Lagrange method in the quasi-coordinate form,and a complete dynamic model of the flexible hypersonic vehicle is establisehd.It lays the foundation of the following study.Secondly,the aerodynamics/flexibility/control coupling characteristics of the flexible hypersonic vehicle are analyzed.In the open-loop case,the equilibrium points of the system under different conditions are obtained.The model is linearized at the equilibrium points.The motion mode and frequency domain characteristics of the flexible hypersonic vehicle are analyzed.In the closed-loop case,the aerodynamic/flexibility/control coupling is analyzed for linear PD control method and nonlinear sliding mode control method respectively,and the analysis results of system stability are given.In addition,the suppression method of aeroservoelasticity is studied,and the commonly used structural filters in engineering are improved.The limited memory adaptive structural filter is proposed.The effectiveness of this method is verified by simulation.Finally,for the parameter uncertainty of FHV,the robust stability of rigid / elastic / control coupling is analyzed.Thirdly,the joint state/parameter estimation method of the flexible hypersonic vehicle is studied.Without adding other kinds of sensors,the states and parameters are estimated jointly by using the measurement of the existing gyroscope for the use of the controller.To improve the estimation accuracy,the problem of sensor placement is studied,and the optimal sensor placement scheme is obtained.Then a new moving horizon estimation algorithm is introduced.The stability of the algorithm is analyzed and the sufficient conditions of stability for the algorithm are given.Based on this,a new arrival cost update algorithm based on QR decomposition is proposed in the framework of moving horizon estimation.Simulation results demonstrate that the algorithm can effectively improve the estimation accuracy and computation speed.Finally,the attitude control problem of the flexible hypersonic vehicle is studied.The attitude control system of the flexible hypersonic vehicle is designed.Roll channel control system uses non-singular fast terminal sliding mode control method and pulse width modulator to stabilize the roll angle.Control system of lateral and longitudinal Channels consists of a moving horizon estimator,a sliding mode disturbance observer and an adaptive hierarchical sliding mode controller.The moving horizon estimator estimates the states and parameters utilizing the gyroscopes' measurement.The sliding mode disturbance observer estimates the lumped disturbance that consists of higher-order flexible modes,parameter uncertainties and external disturbances.The adaptive hierarchical sliding mode controller,which combines adaptive control with hierarchical sliding mode control,computes the rudder defection according to the command attitude and estimated states.Simulation results demonstrate that attitude and generalized coordinates of elastic modes can converge to the target value in two seconds in the case of nominal and parameter disturbances.The control system can effectively control the rigid body attitude and elastic vibration,while ensure the system stability in the case of input constraints,disturbances and aerodynamic heating.