Robust stability of delta-operator discrete-time systems using frequency-domain graphical approach

Concerns a Delta-operator approach to approximation of an analog system. It has several advantages over the q-operator approximation, including convergence of digital results and models to their continuous counterparts as the sampling rate is increased, so that a uniform set of techniques for the stability and control can be obtained for both analog and discrete-time systems. The Delta-operator formulated systems, which in the limit approach their analog counterparts, seem to be suitable for a straight forward robust stability analysis of digital systems, for the available analog stability techniques may be easily extended to a Delta-operator formulated digital model. In this paper, a review of the Delta-operator formulation of an analog system, and its stability and robust stability analysis techniques are presented. Moreover, some of the existing analog robust stability techniques are evaluated for extension to Delta-operator formulated digital systems