Sliding Mode Observer-based Fault Diagnosis And Fault Tolerant Control For Satellite With Actuator Fault

According to the exsisting statistics,it can be found that nearly 180 on-bit satellites have been broken down during the past three decades.More specifically,about 32 percent of the faults occurred in satellite attitude system and these faults do have an impact on the stable operation of the satellite system.Owing to the harsh working environment and the constaints on the manufacturing process,it is highly possible that actuators mounted on the satellite may malfunction and endanger the stability of the entire control system.Therefore,it is necessary to design a fault tolerant control method for the satellite attitude system with actuator fault scenario.By referring existing results,it can be noted that most of the fault tolerant control methods are based on robust control theory,and they can only deal with the types of faults that are included in the design.As a result,it is important to develop an active fault tolerant control method which can obtain the actuator faults' information in real-time.The key objective of this dissertaion is to utilize the sliding mode observer to diagnose actuator fault,and then design the fault-tolerant controller to meet the proposed attitude control requirements.To address these problems,the main works of this dissertation are as follows:Firstly,based on the fault estimation obserbver terchnique,an active fault tolerant control method is proposed which is aimed at improving the conservation in traditional passive fault tolerant control approach.A fault model is given firtsly in the method to represent the actuator fault types and the corresponding physical meanings are narrated clearly.Based on the adaptive sliding mode observer,the impact caused by actuator is obtained on line.The corresponding active fault tolerant controller is established on the basis of the obtained fault impact and the stability of the whole closed-loop attitude system is guaranteed by Lyapunov method.Secondly,for the possible actuator loss of effectiveness fault and bias fault,a novel active fault tolerant control approach is developed which includes a fault detection observer to detect the occurrence of actuator fault.The occurrence of actuator fault is monitored by fault detection observer with adaptive threshold technique.The bias fault and the efficiency factors are estimated separately by the adaptive fault estimation observer.According to the estimation of actuator bias fault and loss of effectiveness fault,an active fault tolerant controller is proposed by integrating backstepping technique and sliding mode control theory.The attitude stabilization maneuver can be accomplished by the proposed active fault tolerant menthod under actuator fault scenario.Finally,to accelerate the fault estimation process and improve the accuracy of fault estimation,a novel fault estimation observer is introduced which integrates the adaptive control method and sliding mode control theory.Based on the estimation value of actuator fault,the corresponding active fault tolerant controller is designed by using backstepping technique and adaptive control theory.The stability of the satellite attitude system with respect to actuator faulty case is proved by Lyapunov stability theory.In addition,in order to verify the effectiveness of the proposed theoretical approaches,simulations are undertaken and the experimental results demonstrate the desired fault tolerant performance of the proposed fault tolerant control methods for the ssatellite attitude system under actuator fault scenario.