AmericanChemicalSociety.com

Introduction.  Without effective process control, safe, efficient and economic operation is virtually impossible in refineries or other manufacturing processes.  Advances in control theory have led to the development of such powerful techniques as Model predictive Control (MPC) capable of delivering overall high control systems performance.  However, in the control system hierarchy, the effectiveness of any advanced control system responsible for high performance operations remains limited by the base regulatory PID controllers operating below it. As processes and process operations have become more complicated, meeting the stringent demands on these manufacturing processes effectively in the 21st century requires not just more advanced control techniques, but also a fundamentally re-imagined alternative next generation regulatory controller that takes proper advantage of modern digital electronic technology to overcome the weaknesses of current PID controller technology.

Results.  In the second phase of this work we have built on the results of the first phase (namely: the actual development of a 4-mode control scheme; and the development of easy-to-apply tuning rules) and thoroughly evaluated the controller’s performance on a laboratory scale water tank, and on a more complicated pilot-scale physical vapor deposition (PVD) process that is prototypical of 21st century manufacturing. Both sets of experimental results demonstrate the ease of tuning and superior performance of this controller vis-á-vis that of the PID controller tuned using various techniques. Especially with the PVD process, where the process operation requirements were virtually impossible to achieve with the PID controller, the RTDA controller consistently performed as designed, enabling the achievement of the manufacturing objectives, as predicted by the theoretical analyses.

Significance. The results from the experimental validation have confirmed that the new controller, which combines the simplicity of the classical PID controller with the efficiency of model predictive control, while avoiding the tuning problem associated with both, is indeed a viable alternative regulatory controller. The results also indicate that the controller is applicable to a wide variety of processes, but especially with complicated processes with stringent operating requirements.

Publication resulting from this work
Kapil Mukati, Michael Rasch, Babatunde A. Ogunnaike, “An Alternative Structure for Next Generation Regulatory Controllers. Part II: Stability Analysis, Tuning Rules and Experimental Validation, Journal of Process Control, 19, 272–287, (2009).