Descriptor system approach for designing sliding mode functional observers with unknown inputs

This paper addresses the problem of estimating a linear function of the states of a system with unknown inputs using descriptor system approach and sliding mode technique. Sliding mode functional observers proposed in this paper are of low-order and do not include the derivatives of the outputs. New conditions for the existence of sliding mode functional observers are derived. A design procedure for the determination of the observer parameters can also be easily derived based on the derived existence conditions.