Adaptive Robust Control For Spacecraft Attitude System

With the fast development of aerospace technology, spacecraft attitude controlproblem has always been a hot and difficult issue in this field. Now, many aerospacemissions, such as earth observation, formation flying and so on, often requireachievement of the desired states with good control performance. Spacecraft withthe ability of completion of aerospace mission rapidly with high precision canincrease its usage ream to get more valuable information. Spacecraft attitudetracking or maneuver is a typical nonlinear control problem and the controllersynthesis is difficult. The increase of the flexible structure in modern spacecraft alsoled to serious vibration problems. In addition, the spacecraft in orbit is affected byvarious environmental disturbance torques; at the same time, the deviations of thecontrol torques caused by the implementation of parts of the spacecraft installationerror also affect the accuracy of attitude control. The traditional spacecraft attitudecontrol method has not been gradually adapted to the many new aerospace missions.With the development of control theory, many nonlinear control schemes are used tosolve the problems of spacecraft attitude control. Under this background, thisdissertation focuses on spacecraft attitude control, flexible vibration suppression andattitude control considering a solar array. The main researches are given as follows:(1) As the foundation of the controller analysis and synthesis in latter chapters,the kinematic equation and dynamic equation are formulated, and the mutualcoupling between the spacecraft dynamic and the solar array drive assembly areespecially given. Then, the model and control of the flexible spacecraft maneuverused as an example, a frame of spacecraft simulation with symbol calculation isproposed in this chapter which is the basis of the simulation platform design anddevelopment latter.(2) Considering the attitude tracking control problem of the rigid spacecraftactuated by fly-wheels, a control scheme based on adaptive robust method ispresented and the stability is proved strictly. Feedback linearization method is thefoundation of the proposed control method and radial basis function neural networkis introduced to design compensation law. In the following part, considering theactuator outputs are limited in actual applications, for the tracking problem of aclass of nonlinear Hamilton system with control saturation, a anti-windup robustadaptive control law is studied based on feedback linearization theory, whereextended state observer is constructed to estimate and reduce the influence ofexternal disturbances and san auxiliary signal is introduced into the control law to compensate for the effect caused by control saturation, then the stability of theclosed loop system is analyzed based on Lyapunov theory. Based on the methodabove, a spacecraft attitude controller considering saturation is designed. Thefollowing numerical simulation is given to illustrate the efectiveness of thedesigned controller.(3) A robust adaptive decentralized control algorithm for a flexible spacecraft isproposed in the presence of external disturbances and parametric uncertainties,which can guarantee the attitude track the command signal accurately. In the designprocedure, the model of the flexible spacecraft is divided into three sub-loops forcontroller synthesis separately and the extended state observer is introduced to getand compensate the nonlinear coupling among the sub-loops and externaldisturbances, then an adaptive law is designed to estimate the uncertain parameters,at last the robust control part is used to achieve the stability of the closed loopsystem. Considering the drawback of the above method, for high attitude controlaccuracy and good flexible appendage vibration suppression effect, the LQR methodis used to design the active vibration controller to ensure the fast decay of theflexible vibration. In order to reduce the blindness of parameter selection, a Q, Rmatrix selection method is given; in the attitude controller design procedure, theproposed method is still based on feedback linearization theory and the dynamicfuzzy neural network (D-FNN) is used to design the compensation scheme for theuncertain parameters. The structures and rules of the D-FNN can be dynamicallyadjusted according to the performance, which can effectively avoid the irrationalityof the selection of the traditional neural network structure and parameters, after that,the robust control part based on the bounded function, which is obtained from theflexible appendage vibration and external disturbances analysis, is added to theattitude control law to ensure the performance of the entire system.(4) For improving the performance of flexible spacecraft attitude control with thespeed fluctuation of the solar array drive assembly (SADA), composite control ofthe spacecraft attitude and SADA is presented for the earth-orienting mission.Taking into account most of the SADA using open-loop control lead to speedfluctuation, an angular rate closed-loop robust control law is developed based oncoordinate transformation and feedback linearization method and the extended stateobserver is added to the control law to reduce the disturbance torque for improvingthe drive rate stability. On this basis, for the attitude regulation problem in theearth-orienting mission, a forward compensation algorithm is given to reduce theimpact of the SADA, and to ensure a high-precision attitude control. Theeffectiveness of the algorithm above has been verified via numerical simulation.Considering the complexity of the simulation program developed, a modular, easily expandable and spacecraft control simulation platform is proposed to reduce thedifficulty of design and improve development efficiency. The platform functionalrequirements are refined from the mission background and the simulation tasksoftware architecture is described based on the hierarchical design. From the view ofcontrol system design, the models of the components of spacecraft navigation,guidance and control are built on MATLAB/Visual C++software. In order toensure that the models of the components and the simulation parameters can beflexible configuration according to the different simulation missions modelmanagement system based on the user interface is designed, the entire simulationplatform is completed.