The Flexible Satellite Attitude Control With Input Saturation

The flexible satellite attitude system is a nonlinear system with multi-input and multi-output.Due to the coupling of the flexible attachment with the center rigid body,satellite attitude motion will excite flexible attachment vibration and flexible vibration will affect satellite attitude motion in turn.In addition,the operation of the satellite in orbit is inevitably affected by external disturbance torque such as aerodynamic torque,solar radiation torque,so it is necessary to consider its ability of interference suppression in the control system design.The actuator can only provide limited torque because of modern satellite’s own physical limit,which will cause the input saturation easily.The input saturation not only reduces control performance of the close-loop system greatly,but also seriously affect the system stability.Base on the above problem,an anti-windup-based H∞control scheme is proposed for the three-axis flexible satellite attitude.The main contents consist of the following parts:Firstly,the mathematical model of the flexible satellite attitude system is set up.The kinematic equation is described by Rodrigues parameters and the dynamic equation is described by the finite element discretization combined with Lagrange function.The state space form of the mathematical model is collated using modern control theory,and use it as the basis for analysis and research of the later chapter control problem.Secondly,based on the linearized model of flexible satellite attitude system,an reduced-order observer-based state feedback controller is designed by passive control of the flexible vibration,which can guarantee the satellite attitude maneuver rapidly and flexible vibration suppression is effective,and keep balance between dynamic performance and steady state performance of control system.The simulation results prove the feasibility of the method and is compared with a nonlinear controller.Again,take input saturation into account of the satellite attitude system,an anti-windup compensation is designed through the actuator input and output to eliminate the influence of saturation.The saturated nonlinear function is dealt with respectively generalized fan inequality condition and traditional fan inequality condition.The former obtain the local stability theory of the closed-loop system and existence conditions of anti-windup compensator through generalized fan inequality condition combined with Lyapunov stability theory,and further expand attraction domain by polyhedron set.The latter study the global stability of the flexible satellite systems with input saturation through the traditional fan inequality conditions combined with Lyapunov stability.Meanwhile,we study the anticipatory activation of anti-windup mechanism in the application of the flexible satellite attitude systems.Finally,in view of external disturbance and input saturation of the flexible satellite attitude system,the paper propose an anti-windup-based H∞ control scheme.The above theory is applied to a flexible satellite attitude control and vast numerical simulation research are done through Matlab/Simulink tools.The simulation results show that the control scheme in this paper can not only guarantee the attitude maneuver of the satellite rapidly,but also suppress flexible vibration and the external disturbance effectively.