Active Fault-Tolerant Control of a Prototype Helicopter Against Actuator and Sensor Faults

This article proposes a novel active fault-tolerant control (FTC) scheme for a 3-degree-of-freedom (3-DOF) prototype helicopter that is instrumented only with angular position measurements, and subject to actuator and sensor faults. The absence of velocity measurements makes it very challenging to design observer-based fault detection and isolation (FDI) and fault estimation (FE) units, which are integral in active FTC. We develop an FDI unit consisting of two reduced-order adaptive interval observers to detect and locate the fault. From the information on the fault location, an FE unit is designed to determine the fault magnitude, by solving the Volterra integral equation (VIE). Using the information from the FDI and FE units, an active FTC scheme is constructed to ensure that the helicopter still functions at a satisfactory level. Compared to previous works, the proposed FDI unit can accurately detect and locate the fault with a lower computational burden due to the reduced number and also dimension of observers, and the proposed VIE-based FE unit removes the necessity for the restrictive matching and minimum phase conditions. Finally, simulations and experiments on the prototype helicopter platform are conducted to verify the effectiveness of the proposed scheme.