Disturbance decoupled residual generation with unknown input observer for linear systems

This paper deals with design of an observer for fault detection and isolation in problems with unsatisfied observer matching condition. The method is based on generating auxiliary outputs from the system measurement to compensate any structural unknown input with any relative degree. The introduced auxiliary outputs are obtained from successive integration of the system measurement. It will be shown that the proposed observer estimates exponentially the auxiliary output in absence of fault. Therefore, residual vector generated from the estimated auxiliary outputs and the actual generated auxiliary outputs will be insensitive to the unmatched disturbances, and at the same time, sensitive to the faulty signals. In comparison with similar works, the proposed residual vector will be more robust against noise of measurement because of integration in contrast to differentiation method of the similar works.