Robust Fault-Tolerant Flight Control Design For Small Unmanned Aerial Vehicles

In this thesis,the robust fault-tolerant flight control design approaches for a small unmanned vehicle are investigated.Based on Safety,reliability and acceptable level of performance of dynamic control systems are the major keys in all control systems especially in safety-critical control systems.A controller should be capable of handling the disturbance and uncertainties imposed to the controlled process.The main works are listed as follows:(1)Study of the actuator fault detection and isolation.Fault observer design for the UAV's Actuator System.We design a set of observer-based residuals to generate the residuals which are sensitive to the faults,and the isolation of the faults.Scheme for the detection and isolation of actuator fault in linear systems is proposed.An unknown input observer is constructed to generate residual signals which will deviate in characteristic way in presence of actuator faults,in such a way the transfer from the disturbances to the residuals is zero and the transfer from the faults to the residuals allows fault isolation.(2)Robust PID controller design for UAV system.Describe the PID controller design for an UAV flight control system.We will focus on these main points:pole placement theory,the control design and stability response,model reduction techniques to enhance the performances and robustness of PID controller.The PID-based control design for UAV's flight control system is used to present the control design for the attitude loop which can make the flight dynamics to track a given reference.The design scheme provide pitch design of an Unmanned Aerial Vehicle(3)Fault tolerant tracking control design with transient performance deals with a robust prescribed performance control(PPC)technique for nonlinear UAV systems with unknown dynamics and uncertainties.Prescribed performance function(PPF)is integrated into the control design,such that both the steady-state and transient control performance can be quantitatively studied and strictly guaranteed.For any a priori known initial state condition,bounded signals in the closed loop,as well as prescribed performance for the output tracking error,we propose a systematic control design procedure,where the proportional-like controls are obtained by using the transformed tracking errors with PPF.Eventually extensive simulations are conducted based on linear and nonlinear UAV to validate the convergence performance and the robustness of the investigated control method.