Estimating and accommodating unknown actuator faults with PI observers

Both estimation and accommodation of actuator faults is required to increase the robustness of control systems. Estimation helps in the early detection and characterization of faults, and allows for the scheduling of preventative maintenance before the onset of catastrophic failures. Fault accommodation helps mitigate the effect of faults or age-dependant component degradation, and allows for the design of control systems which incorporate low-cost components. We show that the integral action of the proportional-integral (PI) form of both the Luenberger and adaptive observers can be used to estimate and accommodate actuator faults. Our simulations show that the accurate estimate of fault induced disturbances by the integral action allows a PI observer-based controller to outperform a LQR when unknown actuator faults are present. When adaptation is required to estimate unknown plant parameters, similar results are obtained