Hammerstein model-based correlation UIO method for fault detection of nonlinear flight control systems

Abstract

In this paper, we propose an alternative approach - the correlation UIO method - for fault detection of nonlinear control systems. The approach exploits a property of the Hammerstein model with separable input process, in which case the cross-correlation function between the input process and the residual of a suitably designed linear UIO is decoupled from the nonlinearity. In an application to nonlinear flight-control systems, a Hammerstein model of the closed-loop system is obtained by a novel approach for system identification, in which the input-output correlation functions are used as data. To apply the correlation UIO method, a very weak (compared to disturbances) separable signal (sinusoid) is injected to the closed-loop system as a diagnostic signal. Simulation results based on an F-16 model show that the scheme is able to detect actuator lock-in-place fault even at trim deflection and in straight-level flight, which is the most difficult situation for flight-control fault detection. Moreover, the detection threshold is independent of the fault and control signals; under some assumptions, it can be arbitrarily increased by increasing the amplitude of the diagnostic signal. The simplicity and benefits of the proposed method are demonstrated through comparison with the standard linear UIO design. Copyright © 2010 by Kai-Yew Lum.