Dynamic Modeling And On-orbit Vibration Control Research For Flexible Spacecraft

In this dissertation,the flexible spacecraft is taken as the research object.The research focuses on the modeling of flexible spacecraft system,the vibration control of flexible attachments during periodic interference and attitude maneuvering.The main research contents are as follows:Aiming at the modeling problem of the flexible spacecraft,the basic structure of the unified cluster spacecraft is introduced.The attitude dynamic equations of the spacecraft in vector are derived according to the Newton-Euler method.The deformation of the flexible body is described by finite element method and the vibration equations of the flexible appendage are derived by Lagrange method.The constrained mode method is used to solve the system dynamic equations.In order to facilitating analysis and use,the model is rationally simplified.The influence of piezoelectric materials on the system is analyzed,and the system dynamic equations with piezoelectric intelligent materials is given.It lays a theoretical foundation for the vibration analysis and control of the flexible attachments.In order to solve the problem of continuous vibration of flexible spacecraft attachments caused by periodic disturbance in stable state,a periodic compensation control scheme based on series expansion is proposed.The ratio of disturbance frequency to system frequency and the ratio of compensation torque amplitute to disturbance torque amplitude are taking as mainly parameters.The first and the second criterion of residual vibration are proposed to obtain the best control effect.According to the two criterions,the optimal parameters of four periodic control torques under different frequency ratios are obtained.The simulation results show that each frequency ratio corresponds to an optimal amplitude ratio.When the frequency is relatively low,both two criterions can achieve good vibration suppression effect.The first criterion needs less calculation,but when the frequency is relatively large,the vibration control effect decreases,while the second criterion needs more calculation,but the vibration control effect is still well when the frequency is relatively large.In order to solve the problem that the residual vibration of the flexible attachments is difficult to control effectively,the component synthesis vibration suppression method is introduced.However,the current research on component synthesis vibration suppression method is based on the undamped system.In order to extend the application range of the force component synthesis method to the damped system,the fully adaptive component synthesis vibration suppression method(FACSVS)is proposed.Based on different requirements in engineering,the FACSVS method contain forward component synthesis vibration suppression method and mixed component synthesis vibration suppression method.Several theorems and inferences are given and their proofs are carried out.Then the theoretical proof is given for the robustness of the full adaptive component synthesis vibration suppression method to the frequency variation.Finally,using the momentum wheel as the actuator,the FACSVS method is experimentally verified on a single-axis air-floating platform.The results show that the method has good vibration control effect on the flexible attachments.The research results have improved the theory of component synthesis vibration suppression and expanded the application range of component synthesis method.Aiming at the problem that the components in FACSVS are always discrete,which leads error to the output of the actuator and the reduces the accuracy of the FACSVS mehod,a continuous synthesis optimization method is proposed.The method calculates the Stieltjes integral parameter through the Lambert W function by using the zero-pole compensation principle.The method converts the second component into continuous force gradually changing from zero.This work achieves the synergistic homegenization effect while retaining the vibration control effect.The method improves the disadvantages of synthesis discontinuity.Considering the problem that the FACSVS method has limited robustness to frequency variation in engineering,a strategy based on the Steiglitz-mcBride frequency identification method is introduced.By accurately identifying the low-order frequencies of the system,the precision of the FACSVS is improved.Aiming at the problem that the attitude controllers can not suppression the vibration of flexible attachments in spacecraft attitude maneuver,a strategy combining FACSVS method with attitude control method is proposed.Considering the existence of moment of inertia variation and external disturbance of spacecraft,an adaptive sliding mode variable structure controller based on classical sliding mode variable structure method is proposed.By introducing the sliding mode boundary layer and the update rate of torque parameter,the disadvantages of torque chattering and parameter dependence are eliminated.In addition,for the problem that the actuator has an upper output limitation,another adaptive sliding mode controller considering actuator saturation and ensuring the stability of closed-loop system is proposed.Finally,the joint application of the FACSVS method and the adaptive variable structure controller is realized with the assistance of piezoelectric intelligent materials.The simulation results show that the control strategy without FACSVS method can not suppression the vibration of the flexible attachments.After conbining the FACSVS method,the residual vibration is well controlled and the attitude accuracy is improved.