Adaptive Fault-tolerant Control Techniques For Hypersonic Vehicle With Unexpected Centroid Shift

Hypersonic vehicles have wide application prospects in military and commercial fields due to the high flight speed.However,the complexity and specificity of the dynamics make the high reliability and safety for the control system of hypersonic vehicle.In recent decades,there is a renewed interest in dynamic characteristics of hypersonic vehicle with unexpected centroid shift,actuator fault in order to explore control laws to enhance its safety and target achievement.The control objective of this work is to develop adaptive fault-tolerant control strategies for attitude tracking of hypersonic vehicle,without resorting to the exact knowledge of inertial matrix and despite the presence of variation of inertial matrix,eccentric moment,system uncertainty and input saturation.At first,based on Newton second law and Varignon’s theorem,dynamics of hypersonic vehicle with unexpected centroid shift are established in view of aircraft-body,inertial reference,wind and path coordinator frame.After analysis,the typical features of HSV with unexpected centroid shifty can be summarized as following aspects: 1)system uncertainty;2)variation of system inertial matrix and 3)eccentric moment.Furthermore,the partial failure of the actuator and the input limitation of the system have brought challenges to the attitude fault-tolerant control under abnormal centroid changes.Secondly,it is worth pointing that the variation of system inertial matrix may cause a challenge for the fault-tolerant controller that rests on the inverse matrix of system inertial matrix due to its potential irreversibility deriving from the estimation of its uncertainty.In connection with this challenge,this paper is devoted to the ideas from series expansion,Nussbaum gain,neural network,system state observer,to deliver the relative innovations.To begin with,the inverse matrix of inertial matrix with its uncertainty is handled by neural network and series expansion.For clarity,this inverse matrix of fault-tolerant controller is obtained by the relative Taylor series of an estimated inertial matrix instead of directly calculating its inverse matrix.After that,drawing support from a Nussbaum gain that can adaptively vary the control direction and magnitude based on the tracking error to achieve the FTC without resorting to the inverse matrix of the inertia matrix,it may be another way to cope with that challenge of inertial matrix.In addition,on account of the effects of centroid shift,actuator fault being reflected in the output states of the system,a fault-tolerant control strategy that rests on a designed sliding mode state observer is established without the exact knowledge of inverse matrix of inertial matrix,which is depending on the idea that system controller can be a kind of feedback control by means of estimated state observer.Moreover,adaptive iterative fault tolerant control and adaptive state feedback control based on the assumption of positive definite of inertia matrix may be another way to handle such a challenge.In what follows,with respect to the input saturation problem caused by actuator fault,eccentric moment,the following two compensation are utilized in this work.1)The external anti-windup auxiliary system.The overlarge output of controller that actuator can not touch is fed back to the closed system again with the form of tracking error and control compensation by anti-windup system which can eventually weaken or eliminate the impact of system input saturation constraints.2)An additional system based on unimplemented output of controller is constructed to so that the control output of the system can meet the needs of fault-tolerant control and suppress the occurrence of input saturation in the controller.In addition,another particularly important issue that deserves attention in HSV applications is system state constraint for ensuring the safety of HSV.There are two state constraint strategies studied in this work.For one,turning to the features of barrier-lyapunov function and Lyapunov stability theorem,the states of HSV can be restricted in a admissible aero without beyond the boundary assuming that the initial values of system states have fallen within the designed boundary of barrier.For another,an innovation of barrier-lyapunov function is developed in this work.The purpose is to realize the constraint on the system state when the fault occurs,this designed constraint scheme can strictly restrict states of system for safety,and that such a constraint strategy can weak this constraint effect and release the maneuverability of the aircraft in case of fault-free.The proof of Lyapunov stability theorem and the verification of simulation are shown in this work.This paper has carried out detailed research on the problems of HSV with unexpected centroid shift,system input saturation constraint and system state limitation.Among them,the problem of faulttolerant control caused by the change of the system’s rotational inertia matrix is elaborated from multiple angles to obtain a more complete study and expand new fault-tolerant control strategies.In addition,a modified barrier-lyapunov function is utilized to expend the applicable range of usual state constraints and has explained different perspectives for the subsequent system state constraint problems before and after the occurrence of fault.