Stability Theory for Linear Time-Invariant Plants with Periodic Digital Controllers

This paper considers the control of a linear time-invariant plant by a digital controller composed of a sampler. a periodic discrete-time component, and a zero-order hold. The stability of such a configuration is analyzed in detail. It is shown how closed-loop zeros can be placed using such a scheme. As a consequence. it is proved that the gain margin can be arbitrarily assigned by suitable choice of sampling time and digital controller. The design procedure is constructive, using state-space methods.