Research On Aircraft Attitude Control Method Aimed At Strong Disturbance And Maximum Allowable Damage

With the rapid development of economy and society,the impact of aircrafts on hu-man beings becomes more and more prominent.Modern aircrafts undertake important tasks in commercial,civil and military areas;this poses higher requirements for aircraft-s' maneuverability,reliability and control accuracy.Since attitude control system is a key component of aircraft and it plays an important role in flight stability,the research of attitude control is a very practical work.Aircraft is a complex and highly nonlinear system,and yet traditional control methods cannot meet the control accuracy of mod-ern aircraft.In order to improve the accuracy of aircraft attitude control,the methods of disturbance rejection,sliding mode control(SMC)and back-stepping control,adaptive law and robust control are combined to handle the large aircraft attitude control.At the same time,the attitude control with maximum allowable damage is investigated in the case of aircraft vertical tail damage.The main innovations of the thesis are as follows:(1)After dimensionless change,a nonlinear aircraft model is transformed into a standard state equation.Aiming at the disturbance rejection problem of nonlinear air-craft attitude control,an active disturbance rejection controller is designed based on back-stepping method.To compensate for the model uncertainty,an extended state ob-server(ESO)is used to estimate the unknown variables such that aircraft's attitude an-gle can track the desired trajectory and the state variables of closed-loop system(CLS)converge to the reference state.The stability of ESO and active disturbance rejection controller is analyzed and proved theoretically.Finally,taking Navion aircraft model as an example,the effectiveness of this method is verified by comparative simulations.(2)Robust adaptive control and back-stepping SMC are applied to study the ro-bustness of aircraft attitude control.Firstly,a robust adaptive sliding mode controller is designed with back-stepping method,and an adaptive law combined with SMC is constructed to compensate for the unknown and uncertain parts of aircraft system.This method does not need to know accurately the physical parameters of aircraft model,and only uses the adaptive upper bound of matrix model norm to ensure system's robustness under SMC.The stability of adaptive law and SMC is analyzed and proved theoretical-ly.Finally,the effectiveness of this method is verified by comparative simulations.In addition,the actuator failure scenario is set to test the anti-interference performance of the controller.The simulation results show that the sliding mode variable structure controller has good control performance.(3)An adaptive sliding mode fault-tolerant control(FTC)method based on LMI is proposed for aircraft attitude control with damaged vertical tail.A new nonlinear integral sliding surface is designed for aircraft damage model.By Using LMI tech-nique,the sufficient conditions for the stability of the equivalent kinematic model of the damaged aircraft are given.A damage tolerant controller based on adaptive SMC is designed to analyze the damaged aircraft system.Finally,the effectiveness of the theoretical results is verified by numerical simulation of the damage of the vertical tail structure of the Boeing 747-100/200 aircraft.The numerical results show that the con-trol law has a positive impact on the performance of the CLS,but it has better fault tolerance and robustness to external disturbances compared with the traditional damage aircraft stability control methods.(4)Further,the vertical tail damage model is extended to nonlinear systems,for the chattering problem caused by switching function,and an equivalent sliding mode FTC method based on hyperbolic tangent function is proposed.By means of Lyapunov method,a linear sliding surface and an equivalent sliding mode controller are constructed.It is proved that the CLS under the controller is asymptotically stable;in order to further optimize the control accuracy and weaken the chattering caused by the symbolic function,we use the improved hyperbolic tangent function to replace the symbolic function in the controller,and design an equivalent sliding mode controller based on the hyperbolic tangent function.It is theoretically proved that the CLS under this control method is uniformly asymptotically stable.Finally,taking the Boeing 747-100/200 aircraft model as an example,the feasibility and effectiveness of this method are verified by numerical simulation.