Fault Diagnosis On Satellite Attitude Control System

Satellite Attitude Control System (SACS) is the key subsystem of an artificial satellite. As the satellites are unreachable in remote space, Fault Diagnosis (FD) on SACS is a hot and frontable problem in the FD research area. More importantly, satellite also has other disadvantages, such as the limited onboard resource in satellites, limited operation ability by human being, bad space environment, and more uncertainty. Those entire disadvantages make a requirement that FD of Satellite must has the ability of quickly self-diagnosis and the ability of being tolerant with fault itself. With the requirement on reliability and long-life of key plant or equipment of china and sponsored by china 863 high technique program (2007AA04Z438), aimed on the practical problem of SACS, this thesis do researches on fault detection, isolation, estimation and recovery from three main approach:model-based (quantitive), intelligent-based (qualitative), hybrid-based.Following the model-based approach, fault diagnosis and fault-tolerant problems of SACS are researched. Aimed on the partial loss of effect (LOE) fault of actuators, a combination with adaptive observer and extended state observer is proposed to diagnosis faults and estimate the severity of fault, and fault accommodation based on quaternion-feedback control low is proposed to recover the fault and implement passive fault tolerant in close-loop. Based on the work above, the partial loss of effect (LOE) fault of actuators in SACS can be detected, isolated and accommodated. Aimed on the partial loss of effect (LOE) fault of sensors, FDI based on devoting observer and active fault-tolerant measures with sensor fault in close-loop fault-tolerant based on KX observer is proposed to overcome full LOE and close-loop instability, which results from that partial sensor is wrong, and make SACS being observed in part and stable in close-loop. Based on the work above, Aimed on the partial loss of effect (LOE) fault of sensors in SACS can be detected, isolated and recovery.Following the intelligent-based approach, we do research on FD of SACS based on the real-time signal by using some neural network (NN) techniques. Aimed on the fault of infrared earth sensor, double ELMAN dynamical NNs are used to learn from the transient signal and classify the specified fault modes in order to detect and isolate the faults. Aimed on the real-time requirement of FD and isolation on multiple faults, an improved MALLET wavelet is introduced to obtain the maximum modulus of signal singular point and avoid learning from samples in order to detect fault, and then an improved IDRNN (Improved Dynamic Recurrent Neural Network) is proposed to identify the faults. Based on the works above, we can detect faults and isolate multiple faults based on real-time monitoring signal.Following the hybrid-based approach, a novel FD for Reaction Wheel (RW) by using NN model identification is proposed. Aimed on the fault mode and fault-free mode in RW, multiple BPNN identification model are designed and trained offline, and then all of them are embedded into object system in order to generate diagnosis residuals online. Based on the residuals, RW faults with different severities can be detected and differed. Aimed on the fault estimation (FE) problem depending on model accuracy, grey box neural network model identification and fault estimation is proposed. By inheriting the dynamics of the object system directly and introducing an improved self-defined exciting strategy, the grey box neural network model for normal mode can be obtained to generate diagnosis residuals online as an estimator so that unmatched dynamics can be avoided. Based on the GBNNM model, faults can be detected and estimated but fault models are not essential.Finally, how to develop the software and hardware in order to validate the proposed FD mentioned above is studied. A real-time simulation hardware platform based on xPC Target, which is used to simulate the SACS, is constructed. And then with referring to some type three-axis earth-oriented satellite, a complete SACS model is designed to inject faults and simulate the fault's behavior. Based on the software/hardware platform, faults mechanism can be analyzed and FD can be validated.