The Application Of Intelligent Variable Structure Control In Hypersonic Aircraft

Hypersonic vehicle has gradually become the focus of scientific and technological competition in various countries for its enormous military and economic value.Due to its flight speed and near-space flight environment,hypersonic vehicle is affected by internal and external disturbances.The aerodynamic parameters change drastically,and there is great uncertainty,strong nonlinearity and coupling in hypersonic vehicle.In this paper,considering the aerodynamic parameter perturbation during the flight,the attitude control method of hypersonic vehicle is studied.In this paper,the coordinate system and its variables used during the actual flight of hypersonic vehicle are introduced.The force analysis is carried out and the six-degree-of-freedom attitude model of the hypersonic vehicle is obtained.Considering the wide range of aerodynamic parameters during the flight of hypersonic vehicle,the uncertainty caused by the change of aerodynamic parameters is introduced,and the affine nonlinear model is further deduced and organized in order to design controller.In this paper,single neuron PID controller and PID neural network controller are designed respectively for the longitudinal channel of hypersonic vehicle by combining neural network control and PID control.The simulation results show that the two control methods have achieved good control effects.However,compared with the single neuron PID control,the neural network PID control has superior tracking performance for desired angle of attack.Based on longitudinal channel attitude control system,the three-channel attitude control system of hypersonic vehicle is further studied.The second-order sliding mode can greatly suppress chattering during approaching phase.Therefore,the second-order sliding mode control is designed for the attitude controller of the hypersonic vehicle,which weakens the chattering.At the same time,the fuzzy control is used to approximate the uncertainty caused by the change of aerodynamic parameters and enhance the robustness of the system to aerodynamic parameters.The simulation results show that the fuzzy second-order sliding mode control system of the hypersonic vehicle has superior control performance,no obvious chattering and strong robustness in present of aerodynamic parameter perturbation.Fractional calculus increases the degree of freedom of differential and integral orders,making the design of the control system more flexible.Fractional sliding mode not only has the attenuation property,which can make the sliding surface release energy slowly during approaching phase so as to alleviate the chattering phenomenon,but also has the information storage property to deal with complex aerodynamic parameter disturbances effectively,which enhances the robustness of the system to aerodynamic parameters perturbation.Therefore,two different fractional-order sliding mode attitude controllers are designed for hypersonic vehicle three-channel attitude control system.In the first method,fractional calculus is used to design the discontinuous control of sliding mode control.The attenuation property of fractional calculus is used to alleviate the chattering phenomenon.At the same time,the indirect adaptive fuzzy control is used to approximate the uncertainty caused by the change of aerodynamic parameters,enhancing the robustness of the system to the aerodynamic parameters perturbation.In the second method,fractional calculus is introduced into the equivalent control of sliding mode control.Fractional sliding mode control can deal with complex aerodynamic parameter disturbances and enhance the robustness of the system by the information storage property of fractional calculus.Moreover,the fuzzy control is used to replace the discontinuous control of the sliding mode control so as to attenuate chattering effectively.The simulation results show that the control systems can deal with the uncertainty caused by the change of aerodynamic parameters effectively and have fast tracking speed and high control accuracy for the desired attitude angle.In summary,neural network PID,fuzzy second-order sliding mode and fuzzy fractional sliding mode attitude controller are designed for hypersonic vehicle in this paper.The simulation research is carried out,and the advantages and disadvantages of the above control systems are analyzed.The superior control scheme is summarized and the future work directions are pointed out.