“PLANT-FRIENDLY” SYSTEM IDENTIFICATION: A CHALLENGE FOR THE PROCESS INDUSTRIES Daniel E. Rivera, ∗,1 Hyunjin Lee, ∗ Martin W. Braun ∗,2 and Hans D. Mittelmann ∗∗ ∗ Control Systems Engineering Laboratory Department of Chemical and Materials Engineering ∗∗ Department of Mathematics and Statistics Arizona State University, Tempe, Arizona 85287 Abstract: The term “plant-friendly” system identification has been used within the chemical process control research community in reference to the broad-based goal of accomplishing informative identification testing while meeting the demands of industrial practice. While many different identification topics (such as control-relevant identification, closed-loop identification and optimal input design) can be said to contribute to plant-friendliness in identification, the problem has some unique character of its own. This paper describes some of the issues that motivate plant-friendly identification and presents an overview of some approaches that have been proposed in this topic. The problem of identification test monitoring is presented as a novel means for accomplishing plant-friendly identification. Keywords: plant-friendly system identification, chemical process control, identification test monitoring 1. INTRODUCTION The term “plant-friendly” identification is one that seems to be exclusive to the chemical process control community. The exact origin of the term is not clear, but it first appears mentioned in print in the paper by Pearson et al. (1993). However, articulation of issues related to plant-friendly considerations can be found in literature based on the experience of industrial practitioners (Rivera et al., 1992) or influenced by the demands of practice (Godfrey, 1993). The concept of plant-friendliness in system identifica- tion for the process industries stems from the funda- mental need for informative experiments despite prac- tical requirements to the contrary. Broadly speaking, a plant-friendly identification test will produce data leading to a suitable model within an acceptable time 1 to whom all correspondence should be addressed; phone:(480) 965-9476, email:daniel.rivera@asu.edu 2 Currently with Texas Instruments Inc., 13570 N. Central Express- way, MS 3701, Dallas, TX, 75265 period, while keeping the variation in both input and output signals within user-defined constraints. Exam- ples of plant-friendly constraints (and their impact on process operations) include: • keeping output deviations low to minimize vari- ability in product quality, • implementing a signal of sufficiently short dura- tion to minimize the amount of off-spec product and reduce engineering time associated with an identification test, • keeping move sizes small to satisfy actuator con- straints and minimize “wear and tear” on process equipment. These practical considerations are often in conflict with theoretical requirements (e.g., asymptotic oper- ation, persistence of excitation, etc.) that demand long identification tests under high signal-to-noise ratios. As a result, plant-friendliness often involves a com- promise between the demands of theory (which are for the most part “plant-hostile”) and the demands of To be presented at the 13th IFAC Symposium on System Identification (SYSID 2003) Rotterdam, The Netherlands, August 27-29, 2003 Session: Identification for Process Control - Input Design