Adaptive Fault Tolerant Attitude Control For Spacecraft With Redundant Reaction-wheels

As the aerospace industry continues to explore for deeper space,spacecraft control systems are increasingly demanding on-orbit autonomous control technology and reliability.However,once faults happened on spacecraft in space,the possibility of repair is negligible.Therefore,it is necessary to design an autonomous attitude fault-tolerant control method for the spacecraft to meet certain control requirements in the case of actuator or sensor fault.In response to the above requirements,the main objectives of this dissertation are: attitude fault-tolerant control methods are designed for a spacecraft equipped with redundant reaction-wheels as actuator.Therefore,the key issuse is to the problem of current conservative nature of fault-tolerant controllers,limited actuator input,fast attitude response,and actuator torque distribution optimization in the presence of external disturbances,uncertainties in the spacecraft model,and actuator faults.The main works of this dissertation are as follows:Firstly,considering the issue of installation deviation,the actuator faults and limited actuator input.A third-order sliding mode attitude fault-tolerant control method based on iterative learning observer is proposed.This method integrates the disturbance torque caused by the installation deviation of the actuators,the external disturbance torque of the system and the fault torque of the actuators,and designing the iterative learning observer to perform high accurate observation.Based on this observation information,a third-order sliding mode fault-tolerant controller is designed.This controller enables the spacecraft to achieve high-precision attitude stabilization and satisfies the actuator input constraint.Because the observer can accurately estimate system faults,the conservative nature of the controller is reduced.Secondly,considering the uncertainty of the spacecraft model and the optimization of energy,an inertia-free attitude tracking fault-tolerant control method is proposed.In order to solve the energy optimization problem,this method firstly optimizes the energy consumption of reaction-wheels to obtain the energy optimal distribution matrix.Then adaptive control technology is applied to achieve the attitude tracking fault-tolerant control of the spacecraft.The control method can achieve higher precision attitude performance in the presence of inertia uncertainties.And under the same attitude tracking task,the energy consumption is obviously superior to the similar control method.In order to improve the spacecraft's robustness to model uncertainties and achieve rapid response of the spacecraft attitude.A inertial-free finite-time fault-tolerant control method for attitude tracking is proposed.This method proposes a new kind of fast terminal sliding surface which solved the singularity and system state chattering problem.Attitude tracking fault-tolerant controller is designed based on the fast terminal sliding surface.At the same time,designing a smooth saturation function solves the problem of limited input of the actuators.This method is robust to the uncertainties of the inertia,and the attitude tracking controller can complete the attitude stability in a finite time.Finally,considering the failure of the angular velocity sensor,the inertia uncertainties and the limited input of the actuator,a torque-optimal finite time fault tolerant control method is proposed.This method proposes an inertia-free observer which estimates angular velocity information when angular velocity sensor fails.Then design a novel time-varying fast terminal sliding surface.A novel finite-time fault-tolerant controller based on angular velocity estimation information and time-varying fast terminal sliding surface is designed.Solving actuator input limitation problem by using hyperbolic tangent function.And propose the concept of output margin to optimize system output capability.This method can observe the angular velocity information rapidly and accurately under inertia uncertanties,achieve finite time stability of the attitude,and balance the output capability of the system.