Research On Fault Diagnosis And Fault-Tolerant Control Of Satellite Attitude Control System

Attitude control system is the core subsystem to maintain regular satellite operation.Due to long-term in-orbit work in the harsh environment of space, the components suchas actuators and sensors in the attitude control system continue to perform in-orbitcontrol operations, therefore are prone to faults. Due to the severe consequence of faultirreparability, the satellite attitude control system fault diagnosis and fault tolerant controltechnology has always been a strong concern in the field of aerospace industry.Meanwhile, conventional fault-tolerant attitude control techniques based on precisemodels have limitations to deal with the unknown changes of on-orbit satellite systemmodel parameters caused by mechanical motion, fuel consumption and spaceenvironment. Oriented from the high reliability and long-life requirement for majorfacilities and equipment, and funded by the National Natural Science Foundation ofChina (61104026), the thesis performs in-depth study on fault-tolerant control issues ofsatellite attitude control system with model uncertainties in both theoretical and appliedaspects. The research mainly involves the following points.Considering the existence of noises, unknown disturbances and model uncertainties,an integrity passive fault-tolerant control design method based on robust H∞theory isproposed to deal with the linear uncertain system control problem. It uses linear uncertainsystem model to transform the passive fault-tolerant control problem into the feasibilityof corresponding linear matrix inequalities in the case of actuator/sensor failure. Inaddition, it gives the sufficient condition for system completeness, and fault-tolerantcontroller design method using robust H∞theory. Based on linearized model of satelliteattitude dynamics model, the fault-tolerant robust H∞controller is designed in the case ofactuator/attitude sensor fault states. Mathematical simulation analysis shows that thecontroller can guarantee control performance of satellite attitude control system againstfaults of sudden or slow actuator/attitude sensor changes, therefore have good fault-tolerant performance against known faults.To deal with Lipschitz nonlinear system with unknown disturbance input, an activefault-tolerant control method based on iterative learning-unknown input observer (IL-UIO) is proposed. First, using the principle of decoupling model uncertainties anddisturbance, a nonlinear unknown input observer is designed to guarantee robustness forfault observation. Then based on I/O data of the controlled system, the current faultinformation is estimated with last step fault observation using IL. The estimation is usedto track and detect fault caused system changes, and implement online faultreconstruction. The robust stability and uniform boundness of IL-UIO are proven usingLyapunov stability theory. The proposed method is applied to the design of fault-tolerant satellite attitude controller with actuator faults. Mathematical simulation results showthat IL-UIO can effectively track past fault system and realize tolerance against flywheelfaults with certain guaranteed system performance. The combination and fusion ofmodel-based observer and data driven approach are adopted here to reinforce robustnessof system residual against unknown disturbance input and improve system data usequality.Satellite attitude sensor faults may pollute measurement information of otherhealthy sensors at next time step, and therefore affect accurate determination of the realfault source. To address the problem and unknown changes of satellite dynamics modelparameters, a fault detection, isolation and identification (FDI) method is proposed,which is based on subspace-aided data driven design using PCA and SIM identificationtechniques. First the equivalent space method is used to preprocess measured data andconstruct residual signal. Then the subspace method is employed to identify augmentedobservation matrix to realize robust detection of sensor faults. The order of the equivalentspace is reduced further with linear transformation to reduce online computation. Finally,the proposed method is applied to satellite attitude control problem with sensor faults.Mathematical simulation results show that it can achieve online FDI with unknownsystem model by only using input-output observation, independent on prior faultknowledge. The adoption of reduced-order fault detection and processing effectivelyreduces computation, and makes the method suitable for online satellite applications.State monitoring and system reconfiguration safeguard long-term autonomoussatellite running, and are also key techniques in the development of onboard healthmanagement system. First, a fault-tolerant control architecture of health managementsystem containing state monitoring and system reconfiguration is given. Consideringnonlinear system with unknown disturbance input, the data driven based patternrecognition method is used to design a set of nonlinear fault estimators based on supportvector machine (SVM). It employs historical data in normal operation and faults states ofdifferent kind to achieve approximate detection and isolated estimation of faultinformation. The information and identified system parameters are then used to designlearning observer to realized adaptive fault compensation. The learning algorithm here isexploited to supply controller reconfiguration information and modify feedback controllaw. Theoretical analysis proves error boundness of fault estimation. Finally, simulationdemonstration is performed under the background of autonomous running task of smallsatellite earth observation. Results show system state monitoring and systemreconfiguration can be achieved in the case of unknown actuator faults.