Abstract
This paper presents robust fault detection based on adaptive thresholds for a three axis satellite. For this purpose, first, the attitude control system (ACS) is described as a quasi linear parameter model that includes both bounded parametric modeling errors and measurement noises. Next, using the interval arithmetic tools, an interval linear parametric varying observer is designed to propagate the effect of satellite parametric uncertainties into the alarm limits. This idea enhances the robustness of fault detection system at the decision making stage. In other words, the adaptive thresholds are generated for evaluating the residuals. Obtained results show that the missing alarm rates are minimized by the developed method; also this approach detects small or incipient faults more effectively than the classical robust fault detection algorithms with constant thresholds. In the next part of paper, an isolation algorithm has been proposed using the fault tree approach. Also, an accommodation system has been designed based on reconfiguration of available actuators. Accordingly, after isolation of faulty reaction wheels using the developed fault tree library, the accommodation system turned them off and replaced the suitable magnetic tourqers instead of faulty reaction wheels. Therefore, despite occurrences of several failures in the ACS, attitude control error is kept limited.
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