Gap Metric Based Control of Process with Recycle Streams

Abstract

Abstract In this paper, we investigate the effect of recycle dynamics on the overall closed-loop stability and performance. It is shown that the effect varies for different control structures. A simple gap metric method is then proposed to examine such effects. This method relies on the assumption that we apply a reduced order controller which is obtained by neglecting the recycle dynamics. As a result, we can treat the recycle effects as coprime factor uncertainty, and determine its upper-bound. The ability of the process to handle the effects is evaluated for different control structures by observing their robust stability margin. Simulation studies using a reactor-cooler system demonstrate that the developed procedure is not only able to quantify the effect of recycle dynamics for different control structures, but also useful as a guideline for designing a reduced order, high performance controller for the process with recycle streams.