Unknown Inputs Observers Design for Fault Detection in a Two-Tank Hydraulic System

A technique for design of unknown inputs observers is presented, applied to the solution of fault detection problem. The proposed technique is mainly based on observation of error signals known as residuals, which are obtained by taking away actual input from estimated input. An unknown inputs observer has the estimation error vector in asymptomatic cero tendency as its special feature, without considering unknown inputs or system perturbations. Diagnosis algorithm was satisfactorily tested in a hydraulic liquid level system in simulation as well as real time.