Active Fault-tolerant Control System For Aircrafts With Actuator Fault

Safety and reliability have always been the most critical factors in the aerospace industry.In recent years,frequent aircraft accidents have increased the demand for flight safety and reliability.High-performance and reliable flight rely on a sophisticated attitude control system.As a special attitude control system,the fault-tolerant control system(FTCS)devotes to maintain system stability and an acceptable control performance when an aircraft fails.In general,FTCS can be divided into passive FTCS and active FTCS.Passive FTCS provides robust fault tolerance by controlling all the pre-considered fault modes,which is more conservative.Active FTCS overcomes real-time fault situations through online fault detection and control reconfiguration.To achieve a flexible,rapid,and accurate fault tolerance for aircraft attitude control systems under actuator faults,this thesis conducted research on the active fault-tolerant control system.Firstly,the model uncertainty and external disturbance in the attitude control system can degrade the efficiency of fault detection.Traditional methods which use the relationship between faults and disturbance as the detection criterion face challenges in selecting detection threshold and missed detection.This thesis investigated fault detection by utilizing isolated fault estimation as the detection signal.The isolated fault estimation is generated by a fault observer.The fault signal can be estimated individually without any information about fault/disturbance.Furthermore,to evaluate the detection signal for online prediction,a multi-variable and multi-condition decision criterion was developed.The fault detection module provides an accurate switching time for the reconfigurable controller,improving the control performance of the AFTCS.Secondly,regarding the conservativeness of the reconfigurable control design,by integrating the integral sliding mode control(ISMC)and gain adaptation mechanism,an improved gain adaptation scheme was proposed.A reconfigurable controller with adaptive gain was investigated,such that the balance between robust stability and control conservatism is achieved.By ensuring robustness against disturbances and faults,the convergence of the adaptive gain and the closed-loop system are accelerated,due to the reaching phase elimination of ISMC.Simulation results have verified the effectiveness of the adaptive-gain reconfigurable controller and its ability to minimize control conservativeness.Moreover,aiming at the problem of dynamic state constraint control,a novel adaptive state constraint control method – the adaptive barrier Lyapunov function was proposed.The derived reconfigurable controller ensures that the state can be driven into the prescribed convergence set without any bound knowledge of disturbances and faults.In addition,the barrier update restart mechanism prevents the state from violating the adaptive barrier due to a reference sudden change and/or faults.Moreover,the nonlinear margin function alleviates the input explosion when the state is close to the constraint.The proposed method outperforms existing dynamic state constraint control methods in terms of generality and flexibility.Finally,concentrating on the underactuated control problem caused by the total failure of a control channel,an AFTCS for an underactuated aircraft was proposed.Due to the difference of independent control inputs,the controller designed for a full-actuated system cannot be directly applied to the underactuated one.Therefore,by analysis of the underactuated model,a switching controller with the underactuated angular velocity was designed to overcome its influence on the system stability.Meanwhile,no assumption is made to maintain a constant underactuated angular velocity.Moreover,a failure detection module was developed to detect the failure,such that the control performance would not be compromised.Numerical simulations have shown the effectiveness and the generality of the AFTCS.