| Spacecraft needs to make various maneuvers in the harsh space environment to complete space tasks such as earth observation and docking between spacecraft,so attitude tracking has always been a hot and difficult problem in the field of spacecraft control,how to make spacecraft quickly and accurately keep up with the expected attitude has been the most concerned problem of experts and scholars.In this thesis,the attitude tracking control of spacecraft is studied by using sliding mode control,adaptive control and fault tolerant control.Firstly,an adaptive fault-tolerant control scheme is proposed based on linear sliding mode and a two-phase power reaching law.Then an adaptive finite-time fault-tolerant controller is designed on account of the terminal sliding mode by improving the sliding mode surface.Specific research results are as follows:(1)For spacecraft attitude model with actuator faults,an adaptive fault-tolerant controller is constructed based on a two-phase power reaching law.The design scheme can make the system states converge to the sliding mode plane quickly,and the convergence time is easy to calculate.(2)Aiming at the shortcomings of linear sliding mode surface and asymptotic convergence of system states,a finite-time adaptive fault-tolerant controller is designed based on the terminal sliding mode.Under the action of the controller,the system states approach the sliding mode surface and converge to the equilibrium point faster,and the convergence time is limited and easy to calculate,and has a good control effect.(3)Both of the above two control strategies use adaptive technology to estimate the unknown parameters,effectively enhance the robustness of the system.In addition,through the redundant configuration of actuators,even if one or more actuators completely fail,the remaining actuators can still provide enough control torque to ensure the smooth completion of the spacecraft to track the desired attitude,and improve the reliability of the system. |
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