Research On Attitude Control Of Near Space Vehicle Based On Predictive Sliding Mode Method

Near space vehicle(NSV)is a new type of aerospace vehicle with high military,civilian value and broad development potential.The attitude control performance of NSV determines its ascent,descent,roll,steering and other movements,so design its attitude control system is a meaningful subject.This paper,researches the attitude control problems under the disturbances of uncertain internal parameters and external disturbances based on the mathematical model of NSV established in the issued literatures.The research contents are as follows:(1)According to issued literatures,the existing dynamic model of NSV is discribed in detail.Assuming that the NSV flys in the cruise section,the attitude dynamic model can be linearized based on the principle of small disturbance,therefore the fast and slow loop linear models of NSV are obtained by linearization respectively,which paves the way for the design of the subsequent controller.(2)NSV flying in the cruise stage has small disturbances such as uncertain internal parameters.In order to elimilate the influence of them,a sliding mode control method based on predictive function,referred to as the predictive sliding mode control method(PFCSMC),is designed.This method improves the control performance and accuracy of the controller by introducing predictive functions and improving the sliding mode reaching law,and strictly proves the stability and robustness of the system with the second method of Lyapunov.Aiming at the problem of limited system states and control inputs,constraints are handeled by optimizing system performance indicators.Finally,the method is used to design the fast and slow loop controllers and then the attitude movement is simulated.The simulation results show the effectiveness of the method.(3)When NSV has uncertain internal parameters and external disturbances that make it deviate from the equilibrium point,the PFCSMC method mentioned above cannot meet the requirements of high performance and accuracy any more.In order to elimilate the influence of internal parameter uncertainty and external disturbances,a predictive sliding mode control method based on linear disturbance observer(LDOPFCSMC)is proposed.In this method,a linear disturbance observer(LDO)is designed to estimate external disturbance,which is used to replace the original disturbance with the estimated value and is taken into account in the predictive model.Then the control law is designed based on the PFCSMC method,and the stability of system is proved.Finally,the simulation of the attitude control system verifies the feasibility of the method.(4)The aerodynamic parameters and flight conditions of the NSV will continue to change,and the compound disturbances formed by the uncertain internal parameters and unknown external disturbances in flight are unknown.The designed linear disturbance observer has linear characteristics,therefore it has some limitations in dealing with such disturbances.In order to eliminate the influence of compound disturbances,a robust adaptive prediction sliding mode method based on fuzzy disturbance observer(FDORAPFCSMC)is proposed.This method approximates the compound disturbances by designing a fuzzy disturbance observer.Aiming at the approximation error generated when approaching the compound disturbances,robust adaptive control is introduced to eliminate the error,and the control law is designed based on the nominal control law.Finally,the attitude control system is simulated,and the simulation results show the effectiveness of the method.