Estimation of Multiple Transient Actuator Faults Using Augmented Error Technique

A fault diagnosis scheme for nonlinear uncertain dynamic systems with both abrupt and incipient faults is discussed. An active fault approach is designed that utilizes adaptive laws of augmented error technique in such a way that accounts for matching uncertainties and the occurrence of actuator faults. The main idea is designing the robust fault diagnosis scheme that guarantee stability of the system in the presence of faults. Using the augmented error technique from model reference adaptive control, an observation error model is formulated to give an adaptive diagnostic algorithm which produces the estimate of actuator faults. Changes in the system due to faults are modelled as unknown nonlinear functions. An occurred fault is isolated if the residual associated with the observer remains below its corresponding adaptive threshold, while at least one of the components of the residual associated with all other estimators exceeds its threshold at some finite time. Unknown Input Observer (UIO) is an estimator which is decoupled from the unknown inputs (certain disturbances, or faults) that may be acting on the system. A key design issue of the proposed fault isolation scheme is the derivation of adaptive residual thresholds associated with observer. The simulation result indicate that the proposed algorithm is more realistic, in the sense that better decoupling properties can be assured without knowledge about unknown inputs, and it is potentially useful in the development of a fault-tolerant control system.