Study On The Methods Of Nonlinear Attitude Control And Passive Vibration Suppression For Flexible Spacecraft

Flexible spacecraft is a complex dynamic system with rigid-flexible coupling and multi-inputs and multi-outputs,it has the characteristics of obvious nonlinearity,flexibility,uncertainty,and external disturbances.Those features,posing great challenges to the attitude control with high pointing accuracy and high stability,are the key points and hot issues in recent years.This paper directly targets the nonlinear attitude dynamics of flexible spacecraft,using Lyapunov stability theory and the SOS technique to study the nonlinear and robust nonlinear attitude control problems and to provid an effective new design theory and method for the attitude control design of flexible spacecraft.The main contents are as follows:(1)Considering the problem of large-angle attitude maneuver and passive vibration suppression of flexible spacecraft,a nonlinear stabilization control scheme based on the flexible mode observer is proposed.By establishing the polynomial state-space equation for the attitude system of flexible spacecraft,using Lyapunov stability theory and the SOS technique,the existence conditions of the flexible mode observer-based nonlinear stabilization controller are given,and the validity of the proposed control design method is verified by numerical simulation.This method fully considers the dynamic characteristics of rigid-flexible coupling and achieves the passive vibration suppression by only controlling the attitude of the rigid body.(2)For the attitude control problem of flexible spacecraft with external disturbances,a nonlinear H? output-feedback control design scheme is proposed.By introducing the auxiliary variable,the nonlinear state-space equation is established.On this basis,in view of the difficulty in measuring the flexible mode,a nonlinear flexible mode observer-based output-feedback controller is constructed.By selecting an appropriate Lyapunov function and applying the matrix decoupling technique,the existence conditions of the nonlinear controller are established in terms of some state-dependent linear matrix inequalities(LMIs).These conditions can be directly converted to a convex programming problem with SOS constraints,which effectively overcomes the computational difficulty existing in nonlinear output-feedback control design.(3)For the attitude control problem of flexible spacecraft with parameter uncertainties,external disturbances and input constraints,a robust nonlinear H?output-feedback control design scheme is proposed.Firstly,based on(2),both the external disturbances and the inertial parameter uncertainty are considered,and the uncertainties caused by the perturbations of inertial parameter are treated as the polytope uncertainties.Then using the Lyapunov stability theory,SOS technique and the generalized S-procedure,the existence conditions of the robust nonlinear H? output-feedback controller are given,and the establishment of the separation characteristic is also proved,which greatly reduces the complexity of controller's design and effectively overcomes the difficulty in constructing the Lyapunov function.Then,on the basis of the above nonlinear control design,the problem of input constraints is further considered,and the existence conditions of the nonlinear controller satisfying input constraints are also established,and the validity of the proposed control design method is illustrated by numerical simulation.(4)On the basis of above research methods,the research object is expanded to a more general class of polynomial nonlinear uncertain systems.Considering the output-feedback based robust nonlinear mixed H2/H? guaranteed cost control problem,the solvable convex feasibility/optimization conditions are established.This generalizes the work of this research and improves the existing results.