INPUT ESTIMATION VIA SLIDING-MODE DIFFERENTIATION FOR EARLY OFC DETECTION

Abstract

Robust and early detection of Oscillatory Failure Case (OFC) in the Electrical Flight Control System (EFCS) of new generation aircraft appears to be a challenging problem. OFC leads to strong interactions with loads and aeroelasticity and consequently must be detected in time. This paper proposes a hybrid unknown input observer for robust and early detection of such unauthorized oscillatory events. The technique has been developed during ADDSAFE project. The monitoring strategy is associated with the decision making rules as currently used for in-service Airbus A380 airplane. The observer has two subsystems operating in continuous and in discrete time. The continuous part is based on a high-order sliding-mode differentiator. The discrete part is used to solve on-line a nonlinear equation using a gradient descent method. Robustness and performance of the proposed fault detection scheme are tested using a high fidelity benchmark and intensive Monte Carlo simulations based on several flight scenarios as specified in ADDSAFE project. The performance indicators of the proposed scheme are measured by its detection delay, its propensity to issue false alarms and whether it permits a failure to go undetected.