Probabilistic Model Based Fault Diagnosis With Application To Spacecraft

The scientific tasks performed in deep space require the spacecraft with thecapacity of self health monitoring and self fault diagnosis. From the informationprocessing point of view, the signal estimation, fault detection, fault isolation andinference problem are studied in this thesis. Besides, this thesis makes furtherdiscussion about the implementation of fault diagnosis system based on typicalspacecraft system configuration.For univariate measurement signal, based on empirical mode decompositionmethod, the signal estimation problem is studied in condition with non-redundancyoutput sensor data. Through analyzing the defects of existing signal estimation methodsbased on emprirical mode decomposition, an evaluation criteria based on signal energyand a signal estimation method based on zero crossovers of intrisic mode fuction areproposed. Two different synthetic signals are simulated under different settings, thesimulation results illustrate that the presented energy based signal estimation techniquecan improve signal-to-noise ratio of the synthetic signals obviously. Based on univariatemeasurement signal and probabilistic distribution model, the fault detection problem isstudied. The univariate measurement signal without fault is used to constructprobabilistic distribution model based on Gaussian mixture model, and the probabilisticdistribution model is applied to detection abrupt and incipient fault based on confidencebound. Bus voltage signal in spacecraft power system is simulated to validate thefeasibility of the proposed fault detection method.Based on Dirichlet process mixture model, the estimation problem of state andoutput with unknown noise interference in dynamic system is studied. To reduce theunknown noise interference and get accurate state and output estimation, the Dirichletprocess mixture model is adopted to model the noise. The DPM-EKF filter is proposedto estimate the state of nonlinear system with unknown noise. The simulation resultsshow that the signal-to-noise ratio of state estimation can be improved obviously.Based on Shiryayev sequential probability ratio, the fault diagnosis problem fornonlinear dynamic systems is studied. The online fault detection and isolation algorithmwith unknown fault magnitude is presented based on Shiryayev sequential probabilityratio and posterior predictive distribution. The fault diagnosis task for spacecraft attitudedetermine system can be accomplished through combining the output estimation and theproposed fault detection and isolation algorithm. Through simulation of abrupt fault inangular rate sensor and angular position sensor, the diagnositic results demonstrate thevalidity of the proposed approach. By using probabilistic inference in fault diagnosis, the probability of fault causecan be deduced from probabilistic graph model, the impact of uncertainty existed indiagnosis model can also be mitigated. The insufficiency of Bayesian network inmodeling the independence is analyzed through instances. The directed factor graph isproposed to serve as diagnosis model for representing the fault propagation relationswithin the spacecraft components. For spacecraft with switching operational mode, theapproach for setting up diagnosis model based on directed factor graph is proposedthrough using causal paths between basic elements of hybrid bond graph. In simulationexperiment, a diagnosis model based on directed factor graph is built up base on hybridbond graph of spacecraft power system, and the fault injection is performed in one of itsoperational modes. The effectiveness of the proposed method is supported by the resultof fault diagnosis based on maximum a posteriori criterion.The electrical connection patterns of on-board computer centric structure and buscentric structure are studied based on typical spacecraft configuration. For spacecraftwith bus centric connection pattern, fault diagnosis system with hierarchical structure isproposed. The fault diagnosis system acts as a separated device to be connected into thesystem bus, and carry out different fault diagnosis algorithm within different hierarchy.Based on math model and hierarchical structure, a spacecraft fault diagnosis simulationand verification system, which contains fault diagnosis emulator, actuator emulator,sensor emulator, etc., is designed and constructed through software and hardwaresimulation. The feasibility of the hierarchical structure of fault diagnosis system iscorroborated through hardware-in-the-loop simulation.