A FUNCTION STATE-SPACE APPROACH TO ROBUST TRACKING FOR SAMPLED-DATA SYSTEMS

it is well known that tracking to continuous-time signals by sampled-data systems presents various difficulties. For example, the usual discrete-time model is not suitable for describing intersample ripples. In order to adequately handle this problem we need a framework that explicitly contains the intersample behavior in the model. This paper presents an infinite-dimensional yet time-invariant discrete-time model which contains the full intersample behavior as information in the state. This makes it possible to clearly understand the intersample as a result of a mismatch between the intersample tracking signal and the system zero-directional vector. This leads to an internal model principle for sampled-data systems, and some nonclassical feature arising from the interplay of digital and continuous-time behavior.