Study On Anti-disturbance Attitude Maneuver Control For Three-axis Stable Liquid Filled Spacecraft

When the spacecraft carrying a partially-filled fuel tank perform attitude motion in orbit,the liquid fuel inside the tank will slosh inevitably.The sloshing of liquid fuel will not only affect the stability of the spacecraft attitude motion,but also pose a large challenge to the design of the attitude controller for the filled liquid spacecraft.In addition,there always exist unknown external disturbances in the operating environment of spacecraft,and it will also be influenced by the uncertainty of its own parameters.Therefore,the attitude control system of liquid filled spacecraft is a multi-input multi-output,and coupled uncertain nonlinear system.In order to accomplish the attitude control mission,it is necessary to design attitude controller with strong robustness.In this thesis,the liquid filled spacecraft is taken as the research object,the coupling dynamics model is established and the anti-disturbance attitude controller is designed for the complex spacecraft attitude maneuver.The main research contents of this thesis are presented as follows:(1)The sloshing of liquid fuel in a partially-filled tank is equivalent to a simple viscous spherical pendulum model.The rigid-liquid coupling dynamic equation and the dynamic equation of the spherical pendulum are derived by using the law of conservation of momentum moment,and the control system of the liquid filled spacecraft is further obtained.The coupling control system of a liquid filled spacecraft is compared with a known rigid spacecraft system,and the adverse influence of liquid sloshing on the rigid spacecraft is theoretically clarified.The same PD controller is used to simulate and compare the difference between the derived control system of liquid filled spacecraft and the known control system of rigid spacecraft.The simulation results show that the traditional PD controller can provide good control performance for rigid spacecraft,but it is difficult to obtain good control performance for liquid filled spacecraft.The dynamics system of the rigid-liquid coupling spacecraft is established,which can provide a theoretical model for the control system design and numerical simulation analysis.(2)Variable structure control(VSC)with linear sliding mode and time-varying sliding mode is proposed to solve the problems of attitude maneuver for liquid filled spacecraft with unknown external disturbances and uncertain parameters.Firstly,the design process of the traditional linear sliding mode variable structure is presented,and then the time-varying sliding mode output feedback variable structure control is proposed.The switch model of this controller uses hyperbolic tangent function to replace the traditional symbol function,which weaken the input chattering effect.Simultaneously,the adaptive control technology is used to estimate the attitude gain parameters and the liquid sloshing displacement variables.In order to make use of the advantages of linear sliding surface and time-varying sliding surface simultaneously,a switching mechanism is designed,which can realize the effective switching between linear sliding surface and time-varying sliding surface according to the current state of the system under certain constraints,such that the state of the system will develop in the desired direction.The simulation results show that the control performance of the variable structure control with linear sliding mode and time-varying sliding mode is better than that of any single variable structure control strategy.(3)The attitude control problems of attitude maneuver for liquid filled spacecraft subject to external unknown disturbances,parameter uncertainty,and sensor measurement uncertainty is investigated.The adaptive robust controller is designed by using the classical backstepping control method,the adaptive control algorithm and the nonlinear disturbance observer.In the backstepping control step,the measurement uncertainty is treated as the mismatched lumped disturbance and the matched lumped disturbances,respectively.Then,the corresponding nonlinear disturbance observer is designed to estimate and compensate them by feed-forward effectively.Next,the adaptive control algorithm is used to estimate the sloshing displacement variables of liquid sloshing effectively,and the adaptive output feedback robust controller is further obtained.The simulation results show that the proposed control algorithm not only robust against the lumped disturbances,but also can obtain good control performance for closed-loop system.(4)In order to address the problem of attitude control for spacecraft control system with external unknown disturbances,parameter uncertainty,and control input saturation,a saturated anti-disturbance finite time sliding mode control is proposed.A finite time integral sliding mode disturbance observer is firstly designed to ensure that the lumped disturbance can be estimated and compensated in finite time.Next,based on the fast terminal sliding mode control theory,an anti-disturbance finite time sliding mode control strategy is proposed.To address the problem of control input saturation,the designed disturbance observer is used to compensate the introduced auxiliary variables,thus the constraint of control input saturation is overcome.The simulation results verify the effectiveness and robustness of the proposed control scheme.