Attitude Control Of Large Truss Structure Satellite With Uncertainty

With the rapid development of space technology,on-orbit tasks become much more diverse and complicated.High-precision and high-stability attitude control is the fundamental requirement for all the on-orbit tasks.In order to reduce the launching cost,however,satellites are developed in the direction of multi-structure and large-scale,and the proportion of flexible structures is increasing.The satellite attitude maneuver will stimulate the flexible vibration,and the flexible coupling torque will seriously reduce the accuracy of attitude control.Due to the lack of effective flexible vibration measuring equipments and active vibration suppression actuators,flexible coupling torque and vibration mode coordinates are difficult to obtain.Therefore,designing attitude control laws for large flexible satellites and reducing the impact of flexible vibration have become a hot issue in the field of satellite control.In addition,on-orbit operation for satellite also faces to many challenges,including uncertainties in inertia,flexible mode,and measurement,which make the attitude control law design much more difficult.This paper is devoted to solving the problems of the attitude control for large flexible satellites,investagating the attitude modeling and control approach,designing,and improving the pointing accuracy of load.Considering the uncertainty of the model,a sliding mode control and an adaptive control law are proposed to achieve the attitude stabilization of the satellite with estimating the inertia parameters online.In view of the state constraint and modal uncertainty,the satellite attitude is restricted by the finite time and prescribed performance techniques.Finally,subject to the measurement uncertainty,an observer-based attitude control method for angular velocity information is designed,and the flexible torque is compensated simultaneously.The main contributions of this paper are briefly listed as follows:To describe the relationship between attitude motion,flexible vibration,and dynamics,a recursive approach for flexible multibody system is put forward based upon the analysis of multiple multibody dynamic models.This approach can significantly diminish the number of generalized coordinates in the system and promote the efficiency and accuracy of dynamic simulation.In addition,the model is simplified as per the requirements for the controller design.Aiming at the problem of attitude stabilization of flexible satellites,the variable structure control approach is untilized to develop a sliding mode control law,in consideration of the model uncertainty.Furthermore,a dynamic switching function is introduced to suppress the chattering result from the symbol function term in the traditional sliding mode attitude control law.The Lyapunov method is adopted to prove the stability of the proposed dynamic sliding mode attitude control law.Aiming at the requirement of attitude tracking control and considering the uncertainty of the flexible mode,a class of adaptive terminal sliding mode finite time control law is presented.The singular problem of the terminal sliding mode control law is avoided via a saturation function,and the corresponding relationship between the system states is explicitly given.In addition,a prescribed performance control term is intergrated into the proposed control law.Thereby,the system sliding surface response has a desired dynamic process,and the attitude tracking error and its first-order derivative are constrained.Considering the uncertainty of inertia parameters,an adaptive attitude stabilization control law is developed by adopting the backstepping design approach.The inertia parameters can be estimated in real time,and the attachments vibration is suppressed.For the influence of external disterbance,the L₂ gain from the external disturbance to the output command is always smaller than a given value,meaning the robustness and adaptability of the control system are improved.Finally,the effectiveness of the designed controller is verified by mathematical simulation.For the attitude stabilization problem subject to measurement uncertainty,this paper first assumes that the modal variables of the flexible satellite are fully measurable.By involving a nonlinear filter,a full state feedback design approach is developed which only requires the quaternion and its derivative information.It is well known that the flexible modal is hard to be measured in practical implementation.Hence,a modal observer is developed to obtain the flexible modals,and an observer-based angular velocity control law is designed subsquently.Finally,the effectiveness of the designed controller is verified by numerical simulation.