Research On Stability Margin Identification Of Flight Control System

The aerocraft system identification based on flight test data can effectively verify the aerocraft design model,which is an important prat of for the aerocraft system design.With the development of aerocraft technology,modern aerocraft,especially the hypersonic vehicle,its speed and maneuvering performance continues to improve,need to fly in the complex environment and the changeable flight state,the demand of robustness and stability for flight control system ars increasingly high.Therefore,it is necessary to study the identification method of control system dynamic characteristics and stability margin of the in the flight test.In this paper,the identification method of control system frequency response and stability margin for the closed-loop condition is studied,specifically in following aspects.Firstly,the definition of coordinate systems and the transformation relation between coordinate systems are given.Then,the 6-DOF nonlinear mathematical model of hypersonic vehicle is presented.The dynamic model is linearized,and the equations of longitudinal motion and lateral-direction motion are given.Secondly,the evaluation method of excitation signal is given.The common excitation signals and their characteristics are introduced.According to the characteristics of stability margin identification task,a summed sine wave signal is selected as the excitation signal.The design method and optimization algorithm of excitation signal are studied,which lays a foundation for study of the identification methods and design of the identification schemes.Thirdly,the identification method of flight control system frequency response and stability margin are studied,The excitation method of flight control system frequency domain identification is determined.Chirp-Z transform is introduced,which is used to calculate the frequency domain data,The calculation method of frequency response of single input system and multi input system is given.This paper also introduces the method of evaluating the quality of the test data by coherence function.Finally,with a hypersonic vehicle as the object of the research,according to the typical flight test trajectory,the identification scheme of flight control system stability margin is designed.The design process of the identification scheme is studied,including the design principle of the identification scheme,the design of the identification scheme,the characteristic analysis of the control system,the design of the excitation signal and the simulation of the identification.In the simulation,use a short-tern and small amplitude excitation signal,completed the stability control system of identification.The simulation results show that the identification scheme had no effect on stability and safety of flight test,and the identification method have high precision.The validity of the identification method is proved.