Active Fault-Tolerant Control With Imperfect Fault Detection Information: Applications to UAVs

A major issue in active fault-tolerant control (FTC) is having to rely on uncertain information provided by the fault detection and identification (FDI) algorithm. To achieve a reliable FTC, the controller needs to be robust against FDI uncertainties, namely missed “small” faults and fault detection delays. In this article, the FDI system only needs to indicate which actuator is faulty after a predefined amount of time, but does not need to estimate the actuator fault value or its faulty position. The goal is to design a FTC, which is robust against potentially undetected “small” actuator faults and which guarantees boundedness of the unstable poles for all possible actuator fault types. An adapted μ analysis is developed to analyze the unstable system poles, due to the presence of a fault. It is integrated within a DK-iteration approach to synthesize a controller in a robust control framework with H
_∞
-design objectives. The synthesis is shown on a fixed-wing UAV, where fault-tolerance against single-actuator faults is achieved. Real flight experiments of a UAV with aileron and flap faults show the validity of the approach.