Research On Input Saturation Control Methods For Hypersonic Vehicles Based On Robust Model Predictive Control

Hypersonic vehicle has a good application and development in military and civilian aspects with the advantages of high speed,defense penetration and large flight range.These characteristics have improved the request for actuators.Therefore,research on actuator saturation control has great practical significance for hypersonic vehicles.In this paper,the research work is conducted from three aspects:In this section,a robust model predictive controller(RMPC)designing method is proposed for the nonlinear longitudinal model of the hypersonic vehicle with input saturation.The polytopic linear parameter varying(LPV)model of the vehicle can be obtained using Jacobian linearization and tensor-product(TP)model transformation approach.Based on the model,the saturated RMPC controller is designed,where the convex hull is constructed by the actual and auxiliary state feedback laws to replace the input saturation,and the auxiliary matrix is introduced to decrease the conservatism of the controller.Linear matrix inequality(LMI)is used to solve the controller.The control performance and stability of the close-loop system are guaranteed.The effectiveness of the proposed method is demonstrated by the simulation comparisons with other RMPC controllers.In order to increase the linear approximation precision and effective approximate range for nonlinear systems,feedback linearization is applied to realize the accurate linearization.In this section,considering the single-input-single-output(SISO)affine nonlinear system subject to uncertain parameters and input saturation,a polytopic linear parameter varying(LPV)model with disturbance and state-dependent input saturation is built by the feedback linearization method,and then a robust model predictive controller(RMPC)based on sum of squares(SOS)is proposed.Based on the polytopic RMPC,the weighted state feedback control law is designed.The norm-bounding theorem is introduced to guarantee that predictive states with disturbance can converge to the invariant set.Moreover,the state-dependent input saturation is transformed into the polynomial convex optimization problem using the Legendre polynomial approximation and SOS technique.Then the actual and auxiliary feedback laws can be obtained.The stability of the closed-loop system is guaranteed by the designed SOS-RMPC controller and it can solves the inputsaturation effectively.In the purpose of achieving the tremendous large flight envelope task,based on the method of the SOS-RMPC controller designing for SISO system,a polytopic model with disturbance is built for the hypersonic vehicles subject to uncertain parameters and actuator saturation by feedback linearization to design controller based on SOS method and norm-bounding theorem.In order to improve the computation efficiency,the relative order derivatives of height and speed are approximated to some extent,and Legendre polynomial is employed to approximate the nonpolynomial function.Thus,SOS-RMPC controllers are established for the two subsystems to guarantee the work of tracking tremendous large flight envelope and satisfying the constraints of actuators.