Fault-tolerant Attitude Control Of Modular Flexible Spacecraft Under Wireless Communication

Reinforcing the control system with self-organization,self-diagnosis,self fault tolerance and intelligent operation capabilities is an important development trend of spacecraft in the future,the functional modularity and wireless communication will also become an important means of the spaceborne cyber-physical system integration.The main problem that the modular system needs to solve is the communication problem between subsystems,when the functional modules of the spacecraft control system are connected via the wireless network,the stability and performance of the system have higher requirements on the bandwidth and transmission frequency of the communication channel.It should be pointed out that the bandwidth and communication frequency of the network are often limited.When the bandwidth cannot meet the signal transmission load or the signal interaction is too frequent,the signal blocking and data dropouts may encounter,which leads to the performance degradation and instability.Quantized control and event-triggered control refer to two promising methods in improving the utilization of network resources,which take effects in reducing data communication and reducing signal interaction frequency.In this thesis,we aim to employ signal quantization communication and event-triggered communication schemes to address the attitude control problem for the modular flexible spacecraft with networked control system architecture and limited communication.The main contents of this thesis is presented as follows:(1).Based on the flexible spacecraft control model and actuator fault model,a composite fault observer is designed to solve the problem of fault reconstruction and online estimation of flexible vibration terms.An adaptive neural network is employed to approximate the flexible vibration generated during the attitude maneuvering of the spacecraft,based on which a novel composite iterative learning observer is designed to reconstruct the lumped term of actuator failures and external disturbances.The observer design method and the adaptive law are given explicitly.This method can be used to construct an active fault-tolerant attitude controller,while compensating the influence of actuator failure,flexible vibration and external disturbance on the attitude of the spacecraft.(2).Consider that the attitude control system structure in which the controller-actuator channel is connected via the network,the attitude control problem is studied with actuator faults and input quantization.Motivated by the idea of the Certainty Equivalence,an online estimation of constant actuator faults based on adaptive technology is carried out to eliminate its influence on the stability of the control system.An effective quantization error compensation mechanism is proposed,and an adaptive quantized fault-tolerant attitude controller is designed based on the sliding mode control method.The stability of the system is proved by the Lyapunov stability theory.(3).Considering the attitude control system of flexible spacecraft with input quantization,the observer-based fault-tolerant control is studied,and a performance optimization method of the fault-tolerant attitude controller is proposed.An adaptive iterative learning observer is designed to reconstruct and estimate the fault parameters,external disturbances and flexible vibration items online.Based on the integral sliding mode control method,an attitude controller with fault compensation,disturbance compensation and quantization error compensation is designed.On this basis,the optimal controller is designed for the sliding mode dynamics based on the adaptive dynamic programming method,so that it has the optimal energy consumption and attitude control performance.The designed controller can ensure the bounded stability of the flexible spacecraft’s attitude.(4).Consider that the attitude control system structure where both sensor-controller channel and the controller-channel are connected via the network,the dynamic/static quantizer are employed for state quantization and input quantization,and the fault-tolerant controller design method is explored.First,a dynamic quantization mechanism is proposed,and a strategy for online adjustment of quantizer parameters based on attitude information is given.Different from the traditional attitude controller design method,the controller is constructed using quantized attitude measurements instead of their original values.Based on the fuzzy logic system and robust control,an adaptive fuzzy faulttolerant controller is proposed under the framework of backstepping controller design,which effectively ensures that the faulty system is asymptotically stable in the presence of signal quantization errors and external disturbances.(5).The event-triggered fault-tolerant attitude controller design method is proposed.A switching event-triggered mechanism is employed to reduce the communication frequency of the sensor-controller channel.Based on the event-triggered attitude measurements and the fuzzy logic system approach for approximation of the flexible vibration terms,an event-triggered sliding mode fault-tolerant attitude controller is designed to ensure that the attitude control system is bounded and stable.A rigorous proof procedure is presented to verify that the event-triggered mechanism can effectively avoid the Zeno phenomenon.The simulation results show that the event-triggered controller can greatly reduce the data transmissions frequency in the sensor-controller channel while ensuring the system is bounded.