Robust output-feedback discrete-time sliding mode control utilizing disturbance observer

This paper is devoted to the problem of designing a robust dynamic output-feedback discrete-time sliding mode controller (ODSMC) for uncertain discrete-time systems. The basic idea behind this scheme comes from the fact that output feedback discrete-time sliding mode control (ODSMC), unlike its continuous-time counterpart, does not require to exploit a discontinuous term including the sliding function. Therefore, it is not a vital requirement that the sliding function is expressed in terms of the system outputs only. Furthermore, our observer-based discrete-time sliding mode controller (DSMC) leads to a considerably larger region of applicability. Besides, with the assumption of dealing with slow exogenous disturbances, a methodology is developed which aims to reduce the thickness of the boundary layer around the sliding surface. Moreover, the boundedness of the obtained closed-loop system is analyzed and the bound on the underlying system state is derived.