On Attitude Maneuver Control And Active Vibration Suppression Of Flexible Spacecraft

With the further deepening of space exploration and exploitation,aerospace technology has become a key technique under rapid development within nations.Modern space missions such as earth observation and formation flying have been increasingly complicated,which make the issues of spacecraft attitude control attract close attention and require increasingly high performance of attitude control systems.In order to achieve the requirements of rapid maneuver and rapid stabilization with very high pointing accuracy and stability,this thesis aims at the actual demand of flexible spacecraft attitude maneuver control and vibration damping.Considering the effects of the rigid-flex coupling,parametric uncertainties and external disturbances,the design approach of high-performance attitude control system that can achieve rapid maneuver with flexible vibration suppression is focused on in this thesis.The main works and contributions lie in the following:To tackle the issues of path planning for flexible spacecraft large-angle rapid attitude maneuver and to reveal the vibration reduction mechanism of smooth paths,this thesis analyzes how the angular acceleration of maneuver path stimulates the flexible vibrations from the perspective of frequency domain,and proposes a novel design idea for path planning composed of two principles,i.e.dominant-frequency placement in stiffness region and less amplitude in damping region.Take the Bang-Coast-Bang path as an example,a selection method of path parameters based on the two principles is proposed.A case study of the Bang-Coast-Bang path design for large-angle rapid slew control of Quanser Rotary Flexible Link system is presented.Theoretical analysis with simulation and experimental results shows that the planned path designed by the proposed method can effectively reduce the stimulation of flexible vibrations during attitude maneuver.Aiming at the issues of high-precision attitude control for flexible spacecraft with parametric uncertainties and external disturbances,two attitude control approaches based on adaptive robust control are proposed in this thesis.On the basis of path planning for less vibration stimulation,an adaptive robust attitude controller based on a projection type adaptation law is designed to guarantee the steady-state performance as well as to improve the transient performance.Furthermore,in order to reduce the effect of measurement noise and to improve the functionality of adjustable model compensation,a desired compensation adaptive robust attitude controller is designed to save on-line computation time and a higher control precision can be obtained.Meanwhile,to suppress the flexible vibrations stimulated by attitude maneuver.an active vibration controller for flexible appendages based on positive position feedback is designed to achieve rapid maneuver and rapid stabilization with vibration suppression.Theoretical analysis and simulation results demonstrate the effectiveness of the proposed two control approaches.In allusion to the issues of asymptotic stabilization and disturbance rejection for flexible spacecraft attitude maneuver in the presence of disturbances,a feedback control method is proposed to guarantee the convergence of modal variables by means of designing the desired path and stabilizing the angular velocity error.Based on the idea of compensating the effect of disturbances and rigid-flex coupling separately and considering the case of modal measurability,a state-feedback attitude controller is designed to ensure asymptotic disturbance rejection with modal variables converging to zero,which employs an internal-model based compensator.Moreover,for the cases of modal immeasurability and inertia parameter uncertainty,an output-feedback and an adaptive output-feedback attitude controller are designed integrating modal estimation and adaptive control,respectively,which both guarantee the asymptotic stability of the closed-loop system without the measurement of modal variables and the priori knowledge of the inertia parameter.Theoretical analysis and simulation results show that the proposed three control approaches are robust to external disturbances and can achieve fine control for flexible spacecraft attitude maneuver.Directing at the issues of vibration suppression for flexible structures with disturbances and structural frequency uncertainties,on the basis of robust adaptive control,an online frequency estimation method based on the gradient algorithm with parameter proj ection and a dead zone is proposed to guarantee the convergence of estimated values in the presence of disturbances.By utilizing the real-time estimated frequencies to update the frequencies of positive position feedback filters,an adaptive positive position feedback based active vibration controller is designed without the priori knowledge of structural frequencies.Theoretical analysis and simulation results show that the estimated frequencies can approach closely to their true values and the proposed adaptive active vibration control method can suppress the vibrations of flexible structures effectively.The exploration and study on the control system for flexible spacecraft attitude maneuver composed of path planning,attitude controller of central rigid body and active vibration controller of flexible appendage,in conjunction with theoretical analyses,simulations and experiments,verify the effectiveness of the proposed idea,i.e.vibration stimulation reduction by path planning first,then precise tracking,and residual vibration suppression at last.