Research On Fault Tolerant Control Design Of The Flight Control Systems For Fixed Wing Unmanned Aerial Vehicle

An unmanned aerial vehicle(UAV)is a kind of equipment controlled by wireless or programme and carries out given tasks without human,which can be devided into two types of rotor UAV and fixed wing UAV.A fixed wing UAV is big lift-drag ratio,cheap,flexible,covert,simply,no casualties and adaptive,so it has received extensive attention in civil and martial domain and is also our research object.UAV formation flight is strongly required by American department of defense for flight control system(FCS)in the forthcoming twenty year.If wireless fault or disturbance happen in the process of flight,UAVs can not maintain a preset formation,and also the safety of whole group is threaten.Therefore,the use of antidisturbance and fault tolerant control(FTC)must be considered when one designs FCS of single or group of fixed wing UAV,which can improve its security,reliability and maintainability.In 1971 professor Niederlinski brought forth a concept of "integrality control" firstly,fault tolerant control technology has become as a research focus in aerospace fields.The research of fault tolerant control technology proves that it can improve the reliability of complicated flight control system(FCS).Especially in the premise that needn’t increasing the hardware devices,the reliability of flight control system using its inherent function redundancy can be improved by fault tolerant control technology,which reduces the design and maintenance costs for FCS.Fault detection(FD)is one of core technology for flight control system FTC,which can determine fault origin,estimate fault value and predict a potential failure,and also can produce a basis for alarm and self-diagnostic maintenance or reconfigurable control law.In a self-repairing control system,another core technology is the FTC scheme for flight control law.When a larger fault occurs,a useful control law is reconstructed,which can guarantee the safety of aircraft and completeness of task,thereby increase the reliability and maintainability of flight control system.Currently many countries including United States,United Kingdom,France,Israel and other aerospace powerful countries have tried their best to develop fixed wing UAV and FTC technology of it,these countries have accomplished lots of achievements,even some key technologies have begun to be verificated in the engineering.However,in China the research on unmanned aerial vehicle is still in an initial stage.Some basic key researches have been studied by the related universities and institutes,which have done some innovational work.According to the existing results,this paper further develops the fault tolerant control theory about FCS of fixed wing UAV And the control strategy and implementation of the flight control systems for the fixed wing UAV are deeply analyzed and demonstrated under actuator failure,sensor failure and communication failure.This content can be divided into the following five sections:Firstly,the composing theorem and characteristic for whole flight control systems of fixed wing UAV actuator is analyzed.By summarizing the common fault type of UAV actuator,namely saturation,stuck,float and loss of effectiveness(LOE),the actuator fault model is built.For the actuator fault of UAV flight control system,the system characteristic under one and multi-fault mode is discussed.By summarizing the common fault type of UAV sensor,namely stuck,bias,gain change and drift,the sensor fault model is built.The further model basis of FTC algorithm is established by the fault model of UAV built.Secondly,for the complex nonlinear flight control systems of a fixed wing UAV,this study takes into account the effects of parameter uncertainty and unknown disturbance input on the controlled systems.At first,a fault detection observer is developed,which is applied to inspect the time of fault occurrence.Then the study makes use of the adaptive dynamic surface control(DSC)technique designing a novel fault estimation and active fault tolerant cotroller for the flight control system of UAV when the partial loss fault of control effectiveness occurs.In the sense of Lyapunov stability,the dynamic tracking error of the faulty control systems is proved to be ultimate uniform boundedness.Finally,Matlab simulation results are given to verify the good characteristic of fault tolerant of the designed DSC fault tolerant algorithm under LOE of actuator.Thirdly,the complex nonlinear flight control systems model of fixed wing UAV with actuator faults is given,which represents the dynamic characteristics of UAV.A fault diagnosis component is used for fault detection and estimation.According to the fault estimation information,the fault tolerant control scheme is developed by adopting the adaptive dynamic surface control technique,further,a prescribed transient performance of the FTC flight control systems is considered,which both guarantee the ultimate uniform boundedness of the closed-loop control systems of UAV in actuator faulty case.Finally,simulation results are shown that the flight control systems with bias fault of actuator could remain transient performance and the output tracking errors converge to a small neighborhood of zero.Fourthly,for the fixed wing UAV formation flight control systems(FFCS),the effect of external disturbance to the flight control system is taken into account by this study,build the formation control system model in some wireless communication fault case.This study design a novel fault estimation and active fault tolerant controller online using adaptive sliding mode control(SMC).On the basis of Lyapunov function the stability of the closed-loop formation flight control systems is proved.Finally,Matlab simulation example results about UAV FFCS are given to illustrate the effectiveness of the proposed active fault tolerant control strategy when the continurous wireless communication fault occurs.Fifthly,for the fixed wing UAV FFCS,this study takes into account the impact of parameter uncertainty factors to the system model,build the formation control system model in some sensor gain fault case.Based on the generalized extended system approach,a robust passive fault tolerant controller is developed for the formation control systems of UAV that happens unknown time-varying sensor fault.Thus,the purpose of asymptotic accommodation for the closed-loop formation flight control systems with the uncertainty and sensor fault is achieved.Finally,Matlab simulation result about UAV FFCS is demonstrated that the designed robust fault tolerant control algorithm achieves a satisfactory control performance in spite of presence of sensor gain fault.