Research On Robust Model Predictive Control Based On Tube For Hypersonic Vehicles

Hypersonic vehicles have drawn more attention through the whole world due to their significant values in civilian and military areas.However,it makes the controller design of hypersonic vehicles highly difficult because of the property of high nonlinearity,strong coupling,fast time-varying and uncertainty.Therefore,it is a challenge to design a controller with strong robustness.This article mainly considers the robust control of hypersonic vehicles and aims to achieve the stable tracking control.The research work is conducted from the following three aspects.Firstly,for the polytopic linear parameter varying(LPV)model of the hypersonic vehicles with bounded external disturbances,we present a tube-based robust model predictive control(Tube-RMPC).Tube invariant set strategy is introduced for dealing with the unknown bounded disturbances.By designing the optimal control law and state trajectory for the corresponding nominal system,the offline Tube-RMPC control law for the real uncertain system is presented.The proposed control law is the combination of two components.The first component steers the state of nominal system to the equilibrium point.The second component keeps the state of real system with bounded disturbance within a tube whose center is the state of nominal system.Then,the robust asymptotic stability is guaranteed.The actual input constraints are satisfied by employing tighter input constraints for nominal system.The effectiveness of proposed controller is verified by the compared simulation with other RMPC controller.Secondly,the states of hypersonic vehicles may not be able to completely measurred in the actual flight.Thus,we propose an output feedback Tube-RMPC control scheme based on the Luenberger observer for hypersonic vehicles in the presence of unmeasured states and bounded disturbances.A robust polytopic state observer is designed to estimate the attack angle,pitch angle and pitch rate by utilizing the limited information of aLTVtude and velocity.Based on these observed states,we design the output feedback Tube-RMPC controller.Wherein,estimation error and control error are bounded by two robust positively invariant sets respectively.Simulation results show the accuracy of polytopic state observer and the effectiveness of robust output feedback controller.Finally,considering the hypersonic vehicles suffering with random drift fault or lose of effectiveness fault of elevator deflection,a Tube-RMPC passive fault-tolerant control(FTC)method is addressed.The fault is transformed into an additional item.And we should consider the maximum value of transformed fault under the worst case.However,the worst case might not happen in the actual flight.Therefore,we introduce a weighting regulatory factor ?.The control performance and robustness are balanced by adjusting the value of ?.The simulations verify the fault-tolerance capability of proposed method and how the value of ? affect the performance of the system.