Adaptive Interval Observer-Based Fault-Tolerant Control for a 3-DOF Helicopter Without Angular Velocity Measurement

This brief presents a novel active fault-tolerant control (FTC) scheme for an unstable three-degree-of-freedom (3-DOF) helicopter subject to motor faults. The helicopter is instrumented only with angular position sensors and has no independent velocity sensors, which makes its FTC design more challenging. Although some works have developed FTC for helicopters using only angular information, they required stringent assumptions on the system. To circumvent this problem, a reduced-order sliding mode observer (SMO) is first introduced to obtain auxiliary signals, which become the outputs of an analytical system. Next, an interval observer (IO) is designed for the analytical system, and a fault-tolerant controller is established, and their parameters are jointly optimized to ensure that the helicopter performs at an acceptable level, whether there is a fault or not. The IOs use adaptive parameters, which provide tighter bounds, resulting in more accurate estimation of faults. Finally, simulations and experiments on a 3-DOF helicopter platform are conducted to demonstrate the efficacy of our proposed scheme.