Advanced process control: Difference between revisions

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{{Short description|Concept in control theory}}

In [[control theory]] '''Advanced process control''' (APC) refers to a broad range of techniques and technologies implemented within industrial process control systems. Advanced process controls are usually deployed optionally and in addition to ''basic'' process controls. Basic process controls are designed and built with the process itself, to facilitate basic operation, control and automation requirements. Advanced process controls are typically added subsequently, often over the course of many years, to address particular performance or economic improvement opportunities in the process.

{{Refimprove|date=January 2017}}

In [[control theory]], '''Advancedadvanced process control''' (APC) refers to a broad range of techniques and technologies implemented within industrial process control systems. Advanced process controls are usually deployed optionally and in addition to ''basic'' process controls. Basic process controls are designed and built with the process itself, to facilitate basic operation, control and automation requirements. Advanced process controls are typically added subsequently, often over the course of many years, to address particular performance or economic improvement opportunities in the process.

[[Process control]] (basic and advanced) normally implies the process industries, which includesinclude chemicals, petrochemicals, oil and mineral refining, food processing, pharmaceuticals, power generation, etc. These industries are characterized by continuous processes and fluid processing, as opposed to discrete parts manufacturing, such as automobile and electronics manufacturing. The term [[process automation]] is essentially synonymous with process control.

Process controls (basic as well as advanced) are implemented within the process control system, which usuallymay meansmean a [[Distributed control system|distributed control system (DCS)]], [[Programmable logic controller|programmable logic controller (PLC)]], and/or a supervisory control computer. DCSs and PLCs are typically industrially hardened and fault-tolerant. Supervisory control computers are often not hardened or fault-tolerant, but they bring a higher level of computational capability to the control system, to host valuable, but not critical, advanced control applications. Advanced controls may reside in either the DCS or the supervisory computer, depending on the application. Basic controls reside in the DCS and its subsystems, including PLCs.

== Types of Advanced Process Control ==

Following is a list of the best well-known types of advanced process control:

* Advanced regulatory control (ARC) refers to several proven advanced control techniques, such as feedforward, override or adaptive gain (but in all cases, "regulating or feedback"). ARC is also a catch-all term used to refer to any customized or non-simple technique that does not fall into any other category. ARCs are typically implemented using function blocks or custom programming capabilities at the DCS level. In some cases, ARCs reside at the supervisory control computer level.

* Advanced process control (APC) refers to several proven advanced control techniques, such as feedforward, decoupling, and inferential control. APC can also include Model Predictive Control, described below. APC is typically implemented using function blocks or custom programming capabilities at the DCS level. In some cases, APC resides at the supervisory control computer level.

* Multivariable [[Modelmodel predictive control]] (MPC) is a popular technology, usually deployed on a supervisory control computer, that identifies important independent and dependent process variables and the dynamic relationships (models) between them, and often uses matrix-math based control and optimization algorithms, to control multiple variables simultaneously. One requirement of MPC is that the models must be linear (i.e. they must be repeatable at all points ofacross the operating range of the controller). MPC has been a prominent part of APC ever since supervisory computers first brought the necessary computational capabilities to control systems in the 1980s.

* Inferential control: The concept behind inferentials is to calculate a stream property from readily available process measurements, such as temperature and pressure, that otherwise would require either an expensive and complicated online analyzer or periodic laboratory analysis. Inferentials can be utilized in place of actual online analyzers, whether for operator information, cascaded to base-layer process controllers, or multivariable controller CVs.

* Nonlinear MPC: Similaris similar to Multivariablemultivariable MPC in that it incorporates dynamic models and matrix-math based control; however, it does not have the requirement forrequire model linearity. Nonlinear MPC is capable ofcan accommodatingaccommodate processes with models that havewith varying process gains and dynamics (i.e., dead- times and lag times).<ref>http://www.aspentech.com/products/advanced-process-control/aspen-nonlinear-controller/</ref>

* Sequential control refers to dis-continuous time and event based automation sequences that occur within continuous processes. These may be implemented as a collection of time and logic function blocks, a custom algorithm, or using a formalized [[Sequential function chart]] methodology.

* Inferential control: The concept behind inferentialsinferential control is to calculate a stream property from readily available process measurements, such as temperature and pressure, that otherwise wouldmight requirebe eithertoo ancostly expensiveor andtime-consuming complicatedto onlinemeasure analyzerdirectly orin real time. The accuracy of the inference can be periodically cross-checked periodicwith laboratory analysis. InferentialsInferential measurements can be utilized in place of actual online analyzers, whether for operator information, cascaded to base-layer process controllers, or multivariable controller CVs.

* Compressor control typically includes compressor anti-surge and performance control.

* Sequential control refers to dis-continuousdiscontinuous time- and event -based automation sequences that occur within continuous processes. These may be implemented as a collection of time and logic function blocks, a custom algorithm, or using a formalized [[Sequentialsequential function chart]] methodology.

* Nonlinear MPC: Similar to Multivariable MPC in that it incorporates dynamic models and matrix-math based control; however, it does not have the requirement for model linearity. Nonlinear MPC is capable of accommodating processes with models that have varying process gains and dynamics (i.e. dead-times and lag times).<ref>http://www.aspentech.com/products/advanced-process-control/aspen-nonlinear-controller/</ref>

* [[Intelligent control]] is a class of [[Control theory|control]] techniques that use various [[artificial intelligence]] computing approaches like [[Artificial neural network|neural networks]], [[Bayesian probability]], [[fuzzy logic]], [[machine learning]], [[evolutionary computation]], and [[Genetic algorithm|genetic algorithms]].

== Related Technologies ==

The following technologies are related to APC and, in some contexts, can be considered part of APC, but are generally separate technologies having their own (or in need of their own) Wiki articles.

* [[Statistical process control]] (SPC), despite its name, is much more common in discrete parts manufacturing and batch process control than in continuous process control. In SPC, “process” refers to the work and quality control process, rather than continuous process control.

*Batch process control (see ANSI/ISA-88) is employed in non-continuous batch processes, such as many pharmaceuticals, chemicals, and foods.

*Simulation-based optimization incorporates dynamic or steady-state computer-based process simulation models to determine more optimal operating targets in real-time, i.e., on a periodic basisperiodically, ranging from hourly to daily. This is sometimes considered a part of APC, but in practice, it is still an emerging technology and is more often part of MPO.

*Manufacturing planning and optimization (MPO) refers to ongoing business activity to arrive at optimal operating targets that are then implemented in the operating organization, either manually or, in some cases, automatically communicated to the process control system.

*[[Safety instrumented system]] refers to a system that is independent of the process control system, both physically and administratively, whose purpose is to assure the basic safety of the process.

== APC Business and Professionals ==

Those responsible for the design, implementation, and maintenance of APC applications are often referred to as APC Engineers or Control Application Engineers. Usually, their education is dependent upon the field of specialization. For example, in the process industries, many APC Engineers have a chemical engineering background, combining process control and chemical processing expertise.

Most large operating facilities, such as oil refineries, employ a number of control system specialists and professionals, ranging from field instrumentation, regulatory control system (DCS and PLC), advanced process control, and control system network and security. Depending on facility size and circumstances, these personnel may have responsibilities across multiple areas, or be dedicated to each area. There are also manyMany process control service companies that can be hired for support and services in each area.

== Artificial Intelligence and Process Control ==

The use of artificial intelligence, machine learning, and deep learning techniques in process control is also considered an advanced process control approach in which intelligence is used to optimize operational parameters further.

For decades, operations and logic in process control systems in oil and gas have been based only on physics equations that dictate parameters along with operators’ interactions based on experience and operating manuals. Artificial intelligence and machine learning algorithms can look into the dynamic operational conditions, analyze them, and suggest optimized parameters that can either directly tune logic parameters or give suggestions to operators. Interventions by such intelligent models lead to optimization in cost, production, and safety.<ref>{{Cite news |date=2016-04-06 |title=Oil and Gas, AI, and the Promise of a Better Tomorrow |language=en-US |work=[[SparkCognition]] Inc. |url=https://www.sparkcognition.com/oil-gas-ai-promise-better-tomorrow/ }}</ref>

== Terminology ==

*APC: Advanced process control, including feedforward, decoupling, inferential, and custom algorithms; usually implies DCS-based.

*ARC: Advanced regulatory control, including feedforward, adaptive gain, override, logic, fuzzy logic, sequence control, device control, inferentials, and custom algorithms; usually implies DCS-based.

*Base-Layer: Includes DCS, SIS, field devices, and other DCS subsystems, such as analyzers, equipment health systems, and PLCs.

*BPCS: Basic process control system (see "base-layer")

*DCS: Distributed control system, often synonymous with BPCS

*MPO: Manufacturing planning and optimization

*MPC: Multivariable [[Modelmodel predictive control]]

*SIS: [[Safety instrumented system]]

*SME: Subject matter expert

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== References ==

{{Reflist}}

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== External links ==

* [https://web.archive.org/web/20060421092145/http://lorien.ncl.ac.uk:80/ming/advcontrl/apc.htm Article] about Advanced Process Control.

[[Category:Control theory]]