Research On Active Fault Tolerant Control For Spacecraft Attitude Systems With Sensor Faults

Probability of various faults will inevitably maintain growing as the structure and function of spacecraft get more sophisticated.Due to the particularity of spacecraft operating environment,it is too difficult to restore faults through manual operation or ground station support.Therefore,fault tolerant control and its application in spacecraft has been an important research topic.Drawing these issues,this paper is focused on active fault tolerant control design of flexible spacecraft with sensor faults,and the main contributions of this thesis are follows.Firstly,a robust fault estimation observer is proposed based on extend state observer approach.Next,a static output feedback based fault tolerant controller is presented by using the compensated outputs.Based on Lyapunov approach,the unknown gain of controller is characterized in terms of solution to a LMI.Finally,the effectiveness of the proposed approach can be verified by the simulation results.Secondly,this thesis combines fault detection observer and fault estimation filter for the purpose of avoiding increasing the dimensions of observer caused by extend state observer approach.Besides,a dynamic output feedback-based fault tolerant controller is also proposed to the flexible spacecraft in sensor faulty case,which can achieve better control performance and fault accommodation compared with static output feedback based approach.All gains of controller to be designed can be pre-determined by solving LMIs and matrix factorization,so the computational complexity is acceptable.The stability analysis of closed loop attitude system with sensor fault is carried out by Lyapunov approach.Finally,simulation results have shown the well fault tolerant performance of the proposed approach.Thirdly,the merits of adaptive observer and sliding mode are introduced to active fault tolerant control design and an integral sliding mode based fault tolerant controller is proposed in this thesis.Firstly,the sensor fault is transformed into a form of actuator fault,and then a fault detection and estimation approach is provided by using unknown input observer based adaptive fault estimation law.Next,an output feedback based integral sliding mode surface is designed to ensure the dynamic performance of the attitude system by bounded real lemma and LMI technique.Meanwhile,the stability of the closed loop attitude systems under the designed active fault tolerant control scheme is analyzed by utilizing Lyapunov approach.Finally,the effectiveness of the proposed fault tolerant scheme has been justified by simulation result.