Robust Control And Envelope Protection For Post-stall Maneuver Of TVC Aircraft

In recent years,the post-stall maneuverability of the aircraft with thrust vectoring control(TVC)has attracted increasing attention from scholars and research institutions at home and abroad.The flight control system design is considered as a key to the implementation of the post-stall maneuver.On one hand,the complicated nonliearity,uncertainties and coupled nature of aircraft dynamic in the post-stall maneuver make flight control problem more challenging.On the other hand,loss of control occurs easily when aircraft maneuvers at high angle of attack,which presents new subject for the flight envelope protection of the aircraft.In order to make the TVC aircraft have both practical post-stall maneuverability and carefree handling at high angle of attack,this thesis presents a systematically research about the flight control and flight safety problem in the post-stall maneuver.Advanced control methodologies,such as robust control and adaptive control,are applied to construct an incorporated flight control and envelope protection system for the post-stall maneuver.This system will enable the TVC aircraft to perform complex post-stall maneuvers as well as to avoid loss of control at high angle of attack.The ADMIRE aircraft with thrust vectoring is selected as the reseach model in the thesis.Firstly,the nonlinear dynamics of the aircraft during the post-stall maneuver is presented,and the high angle of attack characteristics of the aircraft model is analyzed,such as aerodynamic characteristics,inertial coupling and so on.The maneuvering performance of the aircraft is discussed and compared with other traditional fighters.Flying quality requirements for dynamic response and departure prevention in the post-stall maneuver are provided for the design of the flight control and protection system.Also,four typical post-stall maneuvers are defined as benchmarks to verify the performance of the flight control system of the aircraft.Then,in order to design the control law of maneuver flight and envelope protection,a systematic way of derivation of the control-oriented linear parameter varying(LPV)model is provided for the nonlinear model of the TVC aircraft in the post-stall maneuver by using the state transformation approach.The developed method can avoid tedious calculation of linearization and interpolation at trim points,and capture the nonlinear dynamics more accerately.The LPV model is established based on the angle of attack and the velocity-vector roll rate of the aircraft.In addition,a new rapid iterative algorithm is proposed to calculate the dynamic trim points based on the LPV model,which has higher computation speed than the existing Newton-Raphson method.Furthermore,the switched polytopic LPV technique is used to deal with the nonlinear flight dynamics during the post-stall maneuver.By using the high order singular value decomposition method(HOSVD),the established LPV model is transformed into the switched polytopic LPV represention,which contains two different polytopes,one for the conventional angle of attack and the other for the post-stall the angle of attack.This model is used in LPV synthesis to obtain the robust flight control law of the aircraft.After that,the robust H2/H? synthesis with regional pole placement is used for the obtained switched polytopic LPV system to deal with the multi-objective flight control problem in the post-stall maneuver.Due to the distinct dynamic characteristics of the aircraft between the conventional angle of attack and the post-stall angle of attack,the switching control strategy is introduced to design the flight controller for the post-stall maneuver.A single and a switching state feedback control laws are designed based on the common Lyapunov function and the multiple Lyapunov functions technique,respectively.The two control laws are verified and compared in simulations of the benchmark post-stall maneuvers,and the simulation results show that the switching control law has better performance.Next,a robust dynamic compensator is developed on the basis of the closed loop system constituted by the designed post-stall maneuver control law to eliminate the effect of the gravitational force.The task of the gravitational force disturbance rejection during the execution of the post-stall maneuver is abstracted to a robust output regulation problem for a class of nonlinear systems with multidimensional non-matching external disturbacnce.The existence theorem and parameter condition of the partial state feedback control law for this kind of system are derived according to the general framework for tackling the output regulation problem.The proposed control law is applied to the flight control system,and the correctness and effectiveness of this method are demonstrated through simulations.Finally,the flight safety and envelope protection of the aircraft with thrust vectoring during the post-stall maneuver are considered.The flight envelope for preventing aircraft from loss of control is defined based on the concept of attainable equilibrium set.Meanwhile,the departure susceptibility of the designed post-stall maneuver flight control system for the high performance aircraft is evaluated throughout the flight envelope.After a lot of tests,we find that the aircraft departs from the controlled flight more easily when performs nose-down and accelerated roll with respect to the velocity vector simultaneously.It proves that it is necessary to provide envelope protection control to avoid departure of the aircraft during the post-stall maneuver.A reference management device(RMD)is designed to avoid constraints violation of input and output during the longitudinal pull-up maneuver of the aircraft.Furthermore,an envelope protection system is developed based on the tube model predictive control(Tube-MPC)method,which is imposed on the outer loop of the post-stall maneuver flight controller.The integrated flight envelope protection control system can not only meet the flying quality requirements of the post-stall maneuver,but also prevent aircraft from departure and loss of control.The whole system is tested using the Herbst maneuver and the “Mongoose” maneuver.Simulation results show that the aircraft with the developed system can perform this maneuver accurately and safely.