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Satellites FDI system design using sliding mode observers

This paper presents a fault detection and isolation system for the satellites attitude control. The fault detection and isolation system is based on an innovative bank of sliding mode observers, designed taking into account the satellite nonlinear dynamics. The observers are based on the sliding mode control theory, thus being robust to parametric uncertainties and bounded disturbances. A pseudo-sliding law is used to avoid the chattering effect and to reconstruct disturbances and faults based on equivalent injection signal. The bank of observers contains a total of seven sliding mode observers designed for different working scenarios. The first sliding mode observer is called the global observer and it is used to detect the fault appearance in the system, based on the equivalent injection signal. The other sliding mode observers are used to isolate and report any malfunction that may occur in the satellite's guidance and control unit. In order to reduce false alarms a mean window is used over the equivalent injection signal.