Direct control design in sampled-data uncertain systems

This paper introduces a new direction for design of single input/output, sampled-data uncertain systems within the setting of Quantitative Feedback Theory (QFT). The control system consists of a continuous-time uncertain plant, a discrete-time controller connected via a sample-and-hold device and a discrete-time prefilter for reference tracking. The class of problems considered here includes robust stability, robust gain and phase margins, robust discrete-time tracking and robust continuous-time tracking. The new direction involves a QFT technique where control design is performed directly in the Z-domain. It is shown that QFT bounds can be computed in the Z-domain from a set of quadratic inequalities. A numerical example illustrates the salient features of the developed technique.