Flex Seal Stiffness Estimation in Flex Nozzle Control System Using Extended Kalman Filter

This paper presents the application of extended Kalman filter (EKF) for detection of flex seal stiffness fault in electro hydraulic actuator (EHA) driven flex nozzle control (FNC) system. The extended Kalman filter is applied to the EHA to estimate the states as well as parameter (flex seal stiffness).It should be highlighted that the servo valve current is used instead of the desired piston position as the input to the EKF in order to simplify the state estimation problem which would have otherwise involved a fifth order model. The EKF-based estimator includes complete nonlinear models of hydraulic functions. It is shown that, firstly, under normal (no fault) operating condition, the developed estimator closely predicts the states of the system, using only a few basic measurements. Secondly, in the presence of seal stiffness fault, the level of residual errors between the estimated and the actual seal stiffness, increase significantly indicating the occurrence of fault. The results demonstrate the efficacy of the proposed EKF-based fault detection scheme to promptly and reliably respond to flex nozzle control system´s seal stiffness fault.