Title: Cascade Control of unstable systems with application to stabilization of slug flow
Author: Espen Storkaas and Sigurd Skogestad

Presented at IFAC-symposium Adchem'2003, Hong Kong, Jan. 2004 (original date: June 2003.)

Abstract:
The topic of this paper is the effect of stabilizing control on the remaining control problem.
 In many cases there is no effect. However, stabilization requires the active use of inputs, 
and the underlying unstable pole will appear as an undesirable unstable zero if we are concerned 
with input performance. The implications of this are clearly demonstrated on the application to 
stabilization of severe slugging in two-phase pipeline-riser systems. We find that a controllability 
analysis gives important information for measurement selection and performance limitations.