Chattering-free Sliding Mode Based Attitude Control For Hypersonic Vehicle

Hypersonic-vehicle has the characteristics of time-varying,nonlinear,strong coupling,model uncertainty and external disturbance,and the existence of heterogeneous multi actuators.It is a challenging and meaningful task to design a spacecraft attitude control system with good performance,which can complete the mission in the complicated flight environment and flight condition.Nowadays,because of the simple design,easy implementation,and good robustness to external disturbances and uncertainties,sliding mode control has attracted extensive attention in the design of flight control systems.However,in the actual system,due to the time lag switch,the space lag switch,the system inertia,the system delay and the measurement error,as well as the discontinuous switching characteristics of the sliding mode control,the system is accompanied by high frequency vibration in the sliding mode.To solve this problem,in this paper the chattering free sliding mode control method is mainly studied and applied to the attitude control of hypersonic vehicle.Aiming at the chattering-free sliding mode control for continuous systems,a second-order sliding mode control based on finite-time time-varying sliding mode is designed,whose switching items are placed in the derivative of control law,which effectively weaken the chattering phenomenon and guarantee the global sliding mode and the sliding function second order convergence.And the attitude angle tracking error can converge at the setting time.Furthermore,an adaptive second-order time-varying sliding mode attitude control law is proposed,which simplifies the selection of controller parameters and improves the robustness of the system.Based on the idea that PI controller replaces the switching term,a time-varying sliding mode attitude control law based on PI is proposed,which does not contain discontinuous terms and makes the sliding function converge to a small neighborhood near zero,and the attitude tracking error satisfy the requirements.Then in order to improve the control accuracy of the system,and enhances adaptability and robustness of the system,a time-varying sliding mode attitude control law based on neural network PI is proposed.For the sliding mode control of discrete systems,the chattering phenomenon of discrete sliding mode control are analyzed firstly,then a chattering-free sliding mode attitude control based on the improved reaching law is proposed,which solved the chattering problem of the control law while maintain the high control accuracy.Based on equivalent control,two chattering-free global sliding mode control based are proposed.The chattering problem of control law is solved,and the global sliding mode is introduced to reduce the required maximum control law.Finally,a chattering-free finite time sliding mode control based on equivalent control is proposed,which guarantee the global sliding mode and the attitude angle tracking error converge at the setting time,and further reduce the required maximum control law.