Research On Fault-tolerant Attitude Control Methods For Spacecraft

With the deep space exploration mission in full swing,spacecraft attracts the attention of all countries as a core carrier,and its control systems play a key role.Attitude control system of the spacecraft,as one of the important systems of spacecraft control system,plays an extremely important role in acquiring and maintaining spacecraft orientation process.Especially the safety and stability of the attitude control system are the key to ensure that the spacecraft can complete deep space exploration and other tasks successfully.As we all know,with the strong coupling and nonlinearity of the spacecraft attitude control system itself,along with the payload movement,fuel consumption,solar panels,mess of uncertainty will exist in the moment of inertia;Meanwhile,the complicated environment of deep space will bring some external disturbance;In addition,running in complex environment of deep space for a long time will cause some unavoidable faults to the actuators,and this may affect the security of the attitude control system seriously,and even shorten the life span of the spacecraft itself;Moreover,the actuator saturation and misalignment caused by the violent jitter of the carrier and other components during the launch of the spacecraft also have negative impact on the safety and reliability of the attitude control system.In summary,the existence of these unfavorable factors makes the traditional attitude control methods can not meet the requirements of multi-performance indicators when performing complex tasks.In serious case,the mission may even not be completed at all.Based on these reasons,the goal of this paper is to propose attitude fault-tolerant control schemes with high-security and strong stability for the spacecraft.Combining with sliding mode control,RBF neural network(Radial Basis Function neural network),fuzzy control,adaptive control,extended state observer(ESO),adaptive fuzzy observer and robust control algorithm,novel attitude fault-tolerant control schemes are analyzed with both theoretical analysis and numerical simulation.The main contents of this paper are as follows:Considering that the actuators lose power partially or even totally,a novel RBF neural network based adaptive and robust attitude tracking fault-tolerant controller is designed.First,fast and stable attitude tracking control of the spacecraft is realized using the RBF neural network(RBF NN)with its infinite approximation ability to approximate the total uncertain function,and the sliding mode control with its fast response and strong robustness.The proposed control scheme can not only lower the requirements of model and variables,but also reduce the computational complexity(the control scheme only contains some simple functions),which makes the implementation easier and reduces the conservativeness of the traditional control scheme.The conclusion is drew utilizing Lyapunov theory: the designed attitude fault-tolerant control scheme can ensure all states and attitude tracking errors of the spacecraft system are uniformly ultimately bounded under the influence of inertia uncertainty,actuator fault and external disturbance.Finally,simulation results are presented to demonstrate the effectiveness and feasibility of the proposed control scheme under the circumstances of actuators losing power partially or even totally.On the basis of the above research,compounding with fast nonsingular terminal sliding mode surface(FNTSMS),two kinds of finite time attitude fault-tolerant control schemes are designed for two spacecrafts with different number of actuators.Compared with the general linear sliding mode surface(LSMS),the fast nonsingular terminal sliding mode surface has faster convergence,higher accuracy and avoids singular problem existing in the terminal sliding mode surface(TSMS).Then,combined with the fuzzy control,the chattering phenomenon caused by the sliding mode control(SMC)is greatly weakened,and the robustness and fast convergence of the control scheme are improved.Further,according to Lyapunov theory and finite time stability theory,the stability of two finite time control schemes is demonstrated in principle,and a detailed and strict finite time stability proof process is completed.Finally,by considering the different degrees of actuator fault,the simulation and comparison analysis for two types of spacecraft are carried out,the feasibility and effectiveness of the fault-tolerant control scheme thus to verify.A fuzzy adaptive attitude fault-tolerant control method is designed with the unmeasured angular velocity of the spacecraft and the actuator saturation.First of all,mathematical models for the reaction wheel faults of the spacecraft are established.The spacecraft is considered to be installed with three reaction wheels,meanwhile,the first type and the second type faults are taken into consideration.The unmeasured angular velocity is estimated using fuzzy adaptive observer with better estimation ability and strong robustness.After that,with the backstepping control method with fast response characteristic,a novel output feedback attitude fault-tolerant control scheme is designed.The proposed attitude fault-tolerant control algorithm can ensure high performance attitude tracking effect for the spacecraft with the first type and the second type faults.More importantly,the control scheme also handles the problem of actuator saturation,making the spacecraft no longer subject to physical or energy constraints from the actuators.The control scheme improves the attitude control performance greatly,and enhances the stability of the entire closedloop system.Finally,simulation examples with constant faults and time-variant faults are provided to show the validity of the control method.A novel ESO based fault-tolerant attitude tracking control scheme is proposed for rigid spacecraft with uncertain inertia matrix,actuator faults,actuator misalignment and external disturbances.All uncertainties and external disturbances are considered as the total disturbances,and a novel finite time ESO is designed to estimate and compensate the total disturbances.Furthermore,a fault-tolerant control scheme with fast convergence,high-precision attitude tracking,strong disturbance rejection ability is proposed combined with fast nonsingular terminal sliding mode control technology.It is worth noting that,combining the sliding mode control with the ESO achieves the complementary advantages of the two different control methods.The disadvantages of sliding mode control,chattering phenomena,and the shortcomings of ESO,limited ability to estimate,can be remedied by each other.Thus,the safety and stability of the spacecraft attitude control system are improved remarkably in both principle aspect and technical aspect.Then,according to Lyapunov theory and finite time stability theory,strict finite time convergence of ESO is proven and the concrete convergence time are given.Finally,simulation and comparison results with the other two control schemes further show the effectiveness and advantages of this method.In the end of dissertation,the main contents are summarized and the future research works are presented.