Process facility control systems using an efficient...

Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control

Reexamination Certificate

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C700S045000

Reexamination Certificate

active

06347254

ABSTRACT:

COPYRIGHT NOTICE
A portion of the disclosure of this patent document (software listings in APPENDIX A) contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights and protection whatsoever.
CROSS-REFERENCE TO RELATED PATENT DOCUMENTS
The present invention is related to that disclosed in (i) U.S. Pat. No. 5,351,184 entitled “Method of Multivariable Predictive Control Utilizing Range Control;” (ii) U.S. Pat. No. 5,561,599 entitled “Method of Incorporating Independent Feedforward Control in a Multivariable Predictive Controller;” (iii) U.S. Pat. No. 5,574,638 entitled “Method of Optimal Scaling of Variables in a Multivariable Predictive Controller Utilizing Range Control;” (iv) U.S. Pat. No. 5,572,420 entitled “Method of Optimal Controller Design of Multivariable Predictive Control Utilizing Range Control” (the “'420 Patent”); (v) U.S. Pat. No. 5,758,047 entitled “Method of Prodess Controller Optimization in a Multivariable Predictive Controller;” (vi) U.S. patent application Ser. No. 08/490,499, filed on Jun. 14, 1995, entitled “Method of Process Controller Opeimization in a Multivariable Predictive Controller;” (vii) U.S. patent application Ser. No. 08/850,288 entitled “Systems and Methods for Globally Optimizing a Process Facility;” (viii) U.S. patent application Ser. No. 08/851,590 entitled “Systems for Generating and Using a Lookup Table with Process Facility Control Systems and Models of the Same, and Methods of Operating Such Systems;” (ix) U.S. patent application Ser. No. 09/137,358 entitled “Controllers that Determine Optimal Tuning Parameters for Use in Process Control Systems and Methods of Operating the Same;” and (x) U.S. patent application Ser. No. 09/224,439, entitled “Systems for Generating and Using a Lookup Table with Process Facility Control Systems and Models of the Same, and Methods of Operating Such Systems” (which application is filed concurrently herewith), all of which are commonly assigned to the assignee of the present invention. The disclosures of these related patents and patent applications are incorporated herein by reference for all purposes as if fully set forth herein.
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to control systems for process facilities and, more specifically, to control systems, and models and simulations thereof, using an efficient prediction form and methods of operating the same, all for use to optimize process facilities.
BACKGROUND OF THE INVENTION
Presently, process facilities (e.g., a manufacturing plant, a mineral or crude oil refinery, etc.) are managed using distributed control systems. Contemporary control systems include numerous modules tailored to control or monitor various associated processes of the facility. Conventional means link these modules together to produce the distributed nature of the control system. This affords increased performance and a capability to expand or reduce the control system to satisfy changing facility needs.
Process facility management providers, such as HONEYWELL, INC., develop control systems that can be tailored to satisfy wide ranges of process requirements (e.g., global, local or otherwise) and facility types (e.g., manufacturing, refining, etc.). A primary objective of such providers is to centralize control of as many processes as possible to improve an overall efficiency of the facility. Each process, or group of associated processes, has certain input (e.g., flow, feed, power, etc.) and output (e.g., temperature, pressure, etc.) characteristics associated with it.
In recent years, model predictive control (“MPC”) techniques have been used to optimize certain processes as a function of such characteristics. One technique uses algorithmic representations to estimate characteristic values (represented as parameters, variables, etc.) associated with them that can be used to better control such processes. In recent years, physical, economic and other factors have been incorporated into control systems for these associated processes. Examples of such techniques are described in U.S. Pat. No. 5,351,184 entitled “Method of Multivariable Predictive Control Utilizing Range Control;” U.S. Pat. No. 5,561,599 entitled “Method of Incorporating Independent Feedforward Control in a Multivariable Predictive Controller;” U.S. Pat. No. 5,574,638 entitled “Method of Optimal Scaling of Variables in a Multivariable Predictive Controller Utilizing Range Control;” U.S. Pat. No. 5,572,420 entitled “Method of Optimal Controller Design of Multivariable Predictive Control Utiliting Range Control” (the “'420 Patent”); U.S. patent application Ser. No. 08/850,288 entitled “Systems and Methods for Globally Optimizing a Process Facility;” U.S. patent application Ser. No. 08/851,590 entitled “Systems and Methods Using Bridge Models to Globally Optimize a Process Facility;” and U.S. patent application Ser. No. 09/137,358 entitled “Controllers that Determine Optimal Tuning Parameters for Use in Process Control Systems and Methods of Operating the Same,” all of which are commonly owned by the assignee of the present invention and previously incorporated herein above by reference for all purposes.
Generally speaking, one problem is that conventional efforts, when applied to specific processes, tend to be non-cooperative (e.g., non-global, non-facility wide, etc.) and may, and all too often do, detrimentally impact the efficiency of the process facility as a whole. For instance, many MPC techniques control process variables to predetermined set points. Oftentimes the set points are a best estimate of a value of the set point or set points. When a process is being controlled to a set point, the controller may not be able to achieve the best control performances, especially under process/model mismatch.
To further enhance the overall performance of a control system, it is desirable to design a controller that deals explicitly with plant or model uncertainty. The '420 Patent, for example, teaches methods of designing a controller utilizing range control. The controller is designed to control a “worst case” process. An optimal controller for the process is achieved and, if the actual process is not a “worst case process,” the performance of the controller is better than anticipated.
There are a number of well known PID “tuning” formulas, or techniques, and the most common, or basic, PID algorithm includes three known user specified tuning parameters (K, &tgr;
1
, &tgr;
2
) whose values determine how the controller will behave. These parameters are determined either by trial and error or through approaches that require knowledge of the process. Although many of these approaches, which are commonly algorithms, have provided improved control, PID controller performance tuned by such algorithms usually degrades as process conditions change, requiring a process engineer, or operator, to monitor controller performance. If controller performance deteriorates, the process engineer is required to “re-tune” the controller.
Controller performance deteriorates for many reasons, although the most common cause is changing dynamics of the process. Since PID controller performance has been related to the accuracy of the process model chosen, a need exists for PID controllers that allows for such uncertainty by accounting for changing system dynamics. Further, the requirement for ever-higher performance control systems demands that system hardware maximize software performance. Conventional control system architectures are made up of three primary components: (i) a processor, (ii) a system memory and (iii) one or more input/output devices. The processor controls the system memory and the input/output (“I/O”) devices. The system memory stores not only data, but also instructions that the processor is capable of retrieving and executing to caus

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