Research Of Fault-tolerant Control And Single Event Effect Mitigation Techniques For Spaceborne ATP System

It was recognized that the Free-spacelasercommunication would be the primary method to implement a high-speed Inter-satellite and satellite-to-grounddata linkover the next 10~20 years. To establish and keep a communication link in the case of narrow laser beam and long communication distance, acquisition, tracking and pointing(ATP) subsystem is popularly adopted bysatellite optical communication terminal.The stability and reliability of the ATP subsystem iscrucial to establishing a high quality Inter-satellite or satellite-to-ground data link. Therefore, under complex space environment,the study of the method to ensure the ATP subsystem working stably and accurately in its long task cycle has very important engineering significance.To overcome the aforementioned problems, in this paper, the fault-tolerant control(FTC) scheme for coarse pointing and fine pointing subsystem of ATP system and radiation-harden method for SRAM-based FPGA used in ATP system have been studied respectively to ensure the ATP system working stably and accurately. And the main content can be summarized as follow.To determine whether the actuator or sensor of coarse pointing and fine pointing subsystem is faulty, the fault detection and diagnosis method based on state estimation is analyzed in depth. For a linear system, a fault detection filter is proposed to detect the faulty signal. For stochastic systems with noise,a fault diagnosis method based onKalman filter isdeveloped. In this method,a decision approach called weighted sum-squared residual(WSSR) is adopted to detect the faults and a bank of Kalman filters is used to isolate the faulty signal.Experimental studies on a fine pointing prototype system show that the faulty sensor can be isolated timely and accurately. Meanwhile, the redundant hardware is not necessary for the proposed method, thusthe consumption of the hardware and space is decreased relatively.To provide moreessential and real basis for the proposition of fault-tolerant strategy, it is essential to achieve more detail information about the fault signal. Therefore, a fault reconstruction scheme based on sliding mode observer is discussed in this paper.According to the problem caused by high frequency chattering and the requirement for the upper bounds of the faults,an adaptive PI-based sliding mode observer(APISMO) is proposed by replacing the saturation function in conventional SMO with a continuous term determined by an adaptive PI algorithm.The proposed APISMO can effectively reconstruct the fault signals without any prior knowledge of the faults, which makes it more practical.Asensor fault-tolerant control(FTC) scheme for the fine pointingsystem is developed by combining the fault reconstruction method based on the APISMO and hardware redundancy.The proposed method replaces the triple modular redundancy with dual cold backup.The adaptive PI-based sliding mode observer is adopted todetect the fault signal. And during the backup sensor booting up,for maintaining the normal performance of the closed-loop system approximately, a fault measurement corrected by the APISMO is used as feedback signal.Compared with the fine pointing system using triple modular redundancy(TMR), the proposed scheme could maintain a higher level of reliability with only dual redundancy and less power consumption. The experimental results confirm that the fine pointing system with the proposed FTC scheme is high self-control and could maintain a good tracking despite the presence of the fault,meanwhile, the controller structure and parameters donot need to be changed.According to the effectson the controllers and other electronic devices used in the spaceborne ATPcaused by space radiation environment, the mechanism of the total ionizing dose and single event effect of the space radiation effect is studied in detail. This thesis takes the SRAM based FPGA which is affected by single event effect and widely used in spaceborne electronic devices as the research subject, and then conducts research on the application level-radiation harden technology. The TMR fault tolerant method based on dynamic partial reconfiguration is proposed toprotect against radiation effects. The problem of upset accumulation in convential TMR is erased by dynamic partial reconfiguration used in the proposed method.A finite state machine(FSM)circuit is proposed to synchronize the recovered module with the correct ones.To verify the effectiveness of the application level-radiation harden technology for SRAM based FPGA, an evaluation platform based on fault injection is developed. The platform mainly simulates the configuration bit upset failure caused by single event upset.The fault injection is implemented by loading the modified configuration file to FPGA repeatedly. By comparing the output of the design uder test with that of the reference design, the failure probability of the design under test could be obtained. Experiments show that the proposed platform is able to test and evaluate the performance of the radiation harden scheme functionally.The fault diagnosis and FTC scheme proposed in this paper has been verified by experiments.The TMR fault tolerant method based on dynamic partial reconfigurationand the evaluation platform based on fault injection have been applied in several platforms.