Study On Disturbance Rejection Of The Intelligent Space Rigid Frame

With the rapid development of space optical technology as well as the brilliant achievements in space exploration,researchers have increasingly asked for the high pre-cision images delivered by the space telescopes.The movement of the space telescope in space will be subject to numerous disturbances,especially the low frequency distur-bance,which will cause random vibration or harmonic vibration.The low frequency vibration will seriously affect the precision and instability in imaging.In addition,the main optical path of the space telescope is installed on the support frame.Thus the anti-jamming capability of the support frame will directly influence the stability of the main optical path.Therefore,this thesis studies the disturbance rejection of support rigid frame,so as to realize the transmission of high precision image.An intelligent support rigid frame of space telescope is designed based on the piezoelectric active member.The dynamic model of the system is established by fi-nite element method and modal analysis method,and then the transfer function of the system is obtained.Since the space frame is a high order system,the model reduction is realized by modal truncation method to facilitate subsequent analysis and controller design.In order to verify the rationality and validity of the modal order reduction,the vector fitting algorithm based on the frequency response data of the original system is adopted.The frequency response function of the reduced order system is identified as well as the modal parameters,such as the natural frequency and damping ratio.The simulation results verify the exactitude of the vector fitting in identifying the modal parameters.The effectiveness of reduced order model is demonstrateed in the frequency domain and time domain,respectively.Then,the active disturbance rejection control algorithm is adopted for the reduced order model.It regards the unknown disturbance and modeling uncertainty of the sys-tem as the total disturbance.The real-time estimation and compensation of the total perturbation of the system is realized by the extended state observer and the nonlinear state error feedback control law.In the simulation,the displacement response before and after control is measured to illustrate the effectiveness of the proposed algorithm.Since the parameter setting of the nonlinear state error feedback control law is complicated,the fuzzy control algorithm is introduced to identify the parameters effec-tively.A new composite fuzzy active disturbance rejection controller is designed for the intelligent space rigid frame system,which achieves parameters self-tuning by fuzzy logic inference.Further more,a sufficient conditions for 10 stability of the closed-loop system is obtained according to the passivity theorem.The stability of the system can be analyzed by investigating the gain parameters of the nonlinear state feedback control law.Compared with the conventional active disturbance rejection controller,the fuzzy active disturbance rejection controller not only effectively rejects the disturbance of the system,but also realizes the parameters self-tuning of the nonlinear state error feedback control law objectively.