Robust Fault-tolerant Flight Control Of Civil Aircrafts With Strong Flow Disturbance

With the development of aviation industry, civil aircrafts as a quick and convenient manned conveyance, safety, efficiency, environmental protection, and comfort become the primary goal of civil aircrafts. During cruise flight, civil aircrafts often encounter strong flow disturbance even accompanied by some failures. On the one hand, this results in the civil aircrafts fatigue damage and reduces the service life; on the other hand,this will decrease the ride quality of passengers and increase the burden on the pilot’s steering. Therefore, a flight control system with robust fault-tolerant ability plays a vital role in flight safety and performance of civil aircrafts. In this thesis, a robust fault-tolerant flight control method is investigated for the civil aircrafts with strong flow disturbance and actuator faults. The main research contents are as follows:Firstly, the civil aircrafts are taken as the research object, and the nonlinear mathematical model of the rigid body motion is given. To facilitate the study, based on the small perturbation method, the linear mathematical model of the civil aircrafts is obtained. By selecting the atmospheric turbulence as the strong flow disturbance modeling, the aircraft-turbulence integrated model is established.Then, the strong flow disturbance is regarded as a kind of unknown disturbance, the robust flight control of civil aircrafts with unknow disturbance is researched. For the longitudinal channel, the output feedback controller is designed based on augmented state observer. The unknown disturbance is augmented to the state vector, the controller with the usage of augmented state observer to offsetting the influence brought by external disturbance and model uncertainty. For the lareral channel, the active disturbances rejection controller is developed based on extended state observer. Extended state observer is used to estimate the system’s total disturbance real-time and give corresponding compensation. Simulation results reveal that the designed controller can effectively suppress the unknown disturbance which demonstrates good robustness.After that, in terms of civil aircrafts against atmospheric turbulence, the atmospheric turbulence and actuator dynamic systems are augmented to the lateral motion equation. The LQG/LTR method is adopted in the inner loop to solute the steady-state gain of Kalman filter and optimal feedback controller, combined with the PID controller in the outer loop to meet the dynamic performance index of the system requirements. Simulation results show that the controller can ensure the output of the system accurately track the reference input with a good control effect, enabling smooth flight in the atmospheric turbulence.Next, the lateral channel uncertain system of civil aircrafts with the strong flow disturbance and actuator failures is considered. A more general and more practical continuous failure model is adopted. Based on the Lyapunov method, the robust fault-tolerant tracking controller is designed enabling the stability of the closed-loop system with actuator failures. Simulation results show that the developed robust fault-tolerance tracking controller can suppress the influence brought by model uncertainty and strong flow disturbance.Finally, the lateral channel uncertain system of civil aircrafts with the strong flow disturbance and actuator failures as well as actuator lock-in-place is considered. The control allocation method based on pseudo-inverse is combined with an adaptive robust controller. By solving the linear matrix inequality, the robust fault-tolerant tracking controller is obtained. The stability of the closed-loop system is proved by Lyapunov method. Simulation results show that the developed controller can effectively compensate for the adverse effects brought by actuator failures and actuator lock-in-place and guarantee the dynamic performance index of the system.