Fault Reconstruction And Tolerant Control Technology For Spacecraft Attitude Control Systems

As one of the most important subsystems of spacecraft,the attitude control system helps guarantee the spacecraft to implement its space missions.Because of its bad space environment and continuous fuel consumption,the spacecraft is affected by space disturbances and inertia moment uncertainties,its actuators and sensors and other components often malfunction.In order to ensure the high reliability and maintainability of the spacecraft and improve the fault-tolerant performance of the attitude control system,it is imperative to study its fault reconstruction and fault-tolerant control technology based on the observers'fault estimation and tolerance control of adaptive sliding mode control.Despite of some research achievements,the fault reconstruction of space disturbance,robust noise measurement,the nonlinearity and singularity of finite-time sliding mode control and the chattering phenomenon need to be studied in detail.Therefore,the fault reconstruction theory based on the observer and the fault-tolerance control theory based on non-singular terminal sliding mode and its application in spacecraft attitude control system are studied in the dissertation.The main contributions of the dissertation are as follows:(1)The dissertation uses the descriptor system to estimate the fault of spacecraft's attitude control system.For non-linear descriptor system satisfying Lipschitz conditions,a fast adaptive fault estimation observer design method is adopted,which can significantly improve the quickness and accuracy of fault estimation.Assuming that the actuator and sensor of the spacecraft have fault,the augmented model for the attitude control system is established when the sensor fault act in its augmented state.Because the augmented model has the form of descriptor system,the fast adaptive fault estimation method was adopted to realize the actuator fault estimation,and the simulation results verify the effectiveness of the proposed method.The fault estimation method based on the descriptor system can estimate the fault of the actuator but has many constraints and can not solve parameter matrices.Therefore,using the H_?technology,the robust adaptive and improved robust adaptive fault estimation observer was designed for the space disturbance,and parameter matrix method in systematic of observer is presented using LMI technique.At the same time,expanding the method to the state space model,the actuator fault of spacecraft attitude control system is simulated,and the simulation results verify the effectiveness of the fault estimation method.(2)The actuator fault reconstruction problem of the attitude control system based on the P-type and PD-type learning observers was studied.The fault reconstruction method based on P-type learning observer was studied for space disturbance and measurement noise influence of spacecraft attitude control system.Based on the H_?performance index,and the LMI technique,the robust P-type learning observer was designed according to the Lyapunov stability theory.At the same time,the influence of space disturbance and measurement noise on the actuator fault reconstruction is restrained by using the robust technology.But to reconstruct the fault,the information acquired through the fault reconstruction method has certain steady-state errors,and the physical meanings of fault conditions are not clear.Therefore,the actuator fault reconstruction method based on the PD-type learning observer was proposed.The reconstruction method has the desired robust performance indices and can achieve the accurate reconstruction of the abrupt and time-varying fault in the presence of space disturbance and measurement noise in the attitude control system.Using the H_?performance index to suppress the influence of space disturbance and measurement noise on fault reconstruction and based on LMI technique,the observer matrices were solved.Two learning observers are applied to the attitude control system's fault reconstruction respectively,and the simulation results verify the effectiveness of the fault reconstruction method.(3)The attitude tracking fault-tolerant control for spacecraft convergences in finite time is studied based on the non-singular terminal sliding mode.By introducing the non-singular terminal sliding mode,the attitude tracking fault-tolerant control law with finite time convergence is designed based on parameter adaptive,and the stability of the control law is proved based on Lyapunov theory.For the chattering phenomenon and the dependence on space disturbance of the above control law,a finite-time convergence fault tolerant control strategy based on adaptive non-singular fast terminal sliding mode is proposed by introducing a non-singular fast terminal sliding mode,which can convergence in finite-time and avoid singularities.It is further shown that the controller is independent from a prior knowledge of spacecraft inertia or upper bound of external disturbances with parameter adaptations.The Lyapunov stability analysis shows that the controller designed in this paper can guarantee the fast convergence of the closed-loop system,and has a good fault tolerant performance for actuator faults under multiconstraints on external disturbances,inertia uncertainties and actuator faults.The two different fault-tolerant tracking control laws are applied to the attitude control of spacecraft.The simulation results verify the effectiveness of the proposed control laws.(4)Finite-time convergence control strategies based on adaptive non-singular fast terminal sliding mode are proposed for spacecraft attitude tracking subject to external disturbances,inertia uncertainties,control saturation and actuator fault.A finite-time fault-tolerant attitude tracking controller meeting the multi-constraints is developed by introducing a non-singular fast terminal sliding mode with finite-time convergence and singularities avoidance attributes.It is further shown that the controller is independent from inertia uncertainties and bound of external disturbances with parameter adaptations.In order to further improve the convergence time of the system,a new rapid non-singular terminal sliding mode is selected,which contains the advantages of the common and non-singular terminal sliding mode.Using the sliding mode above and adaptive control,a new method of finite-time convergence control is designed.The Lyapunov stability analysis shows that the designed controller can guarantee the fast convergence of the closed-loop system and has a good fault-tolerant performance on control saturation and actuator faults under the multi-constraints on external disturbances,inertia uncertainties,control saturation and actuator faults.In addition,the controller designed in this paper explicitly considers the actuator output torque saturation amplitude requirements,which makes the spacecraft complete the given operations within the saturation magnitude and without the need for on-line fault estimate.The two adaptive fault-tolerant control laws are applied to the spacecraft attitude control system.The simulation results verify the effectiveness of the control method.