DCS-Based APC (Advanced Process Control) vs MPC (Model Predictive Control)

In this blog we will explain the basis for choosing DCS-based Advanced Process Control (APC) over Model Predictive Control (MPC).  PiControl has extensive skills and experience in making a judicious selection between DCS-resident advanced process control (APC) and a full-blown model predictive control (MPC).  Depending on the plant and process characteristics, DCS-based advanced process control (APC) can be superior, achieve more monetary benefits and outperform a model predictive control (MPC).  PiControl has expertise to help customers evaluate the options and choose the best. 

After detailed process analysis, and based on four criteria explained below, PiControl can easily and honestly recommend which control logic will give the best achievements: DCS-resident advanced process control (APC) or model predictive control (MPC, like DMC/RMPCT).  PiControl is confident that in 75 % of industrial cases DCS-based advanced process control (APC) will save more money, maximize monetary, tangible and intangible benefits and be superior to any model predictive control (MPC like DMC, RMPCT or similar).   

Four decision criteria:

Criteria 1 – Multivariable Nature: Is the overall process multivariable?  Are most of MVs related to more dependent CVs (not only one or sometimes two CVs)?

Criteria 2 – Interactivity: Is the process highly interactive?  Is the process control matrix highly dense (interactive control matrix)?

Criteria 3 – Dynamic Model Shapes: Are process dynamics or responses of any MV-CV pairs complex (inverse response or wavy)?

Criteria 4 – Dead Time/Time Constant Ratio: Is the ratio of process dead time to process time constant in most of MV-CV pairs more than 1.0? 

If most of the criteria have negative answers, in such cases, DCS-resident advanced process control (APC) will work well because a low ratio is a sign of favorable process dynamics.

What are DCS-based Advanced Process Control (APC) benefits compared to Model Predictive Control (MPC)?  PiControl’s advanced process control (APC) approach will provide significant cost savings, faster commissioning and project completion and higher benefits compared to model predictive control (MPC) technologies.  The basis for these benefits is based on the following:

  1. Nowadays most of the industrial plants use powerful and modern DCS systems with tremendous process control and APC functionalities.  PiControl technology can wholly be implemented inside any existing DCS system without a need for an external computer.
  2. 75 % of industrial processes are sequential with a diagonal control matrix, making it very suitable for DCS-based advanced process control (APC) without the need for a full-blown model predictive control (MPC, like DMC or RMPCT).  The feedback corrective action possible by mathematically optimized DCS tuning parameters will provide crisp, stable and tight control action outperforming model predictive controllers (MPCs, like DMC and RMPCT).  PiControl has demonstrated success with DCS-based advanced process control (APC) and has several times outperformed model predictive controllers (MPCs) in the past at other sites. 
  3. Model predictive control (MPC, like DMC/RMPCT) runs on a separate computer requiring OPC connections to the DCS.  This approach requires buying a new computer, all the peripherals, adding and configuring OPC.  All this takes extra time and effort since the configuration of the computer from both systems and applications sides are involved.  The model predictive control (MPC, like DMC/RMPCT) needs to be designed and configured on this external computer which is also an extra step compared to PiControl’s DCS-based advanced process control (APC) approach.
  4. Over the recent years, OPC is becoming increasingly vulnerable to process control security problems.  Many elite companies are moving away from OPC due to network and process control security vulnerability.  PiControl Advanced process control (APC) approach does not need OPC at all.  PiControl advanced process control (APC) does not need an external computer at all since all advanced process control (APC) is implemented inside the existing DCS or a PLC.
  5. PiControl looks at the advanced process control (APC) benefits using a four-pronged approach:
  6. Base-level PID optimization using closed-loop ultra-short duration data without step tests.
  7. Online control quality monitoring of all PID and advanced process control (APC) tags inside the DCS using PiControl’s APROMON software.
  8. Advanced process control (APC) design and implementation inside the existing DCS using PITOPS software.
  9. Providing modern training using PID simulator SIMCET for maintenance and support from plant and DCS engineers.
  10. Model predictive control (MPC, like DMC/RMPCT) does not provide the four components listed in item 4 above and as a result, with time, the advanced process control (APC) benefits from PiControl will be superior because of precise mathematical calculations, online regular monitoring and proactive maintenance and training.
  11. PiControl advanced process control (APC) being all inside the DCS can be easily supported and modified by a compact team of local and remote engineers.  Data analysis for support and improvements can be conducted remotely very efficiently followed by changes on site.  In contrast, an external computer housing the model predictive control (MPC, like DMC/RMPCT) requires computer knowledge and configuration and maintenance knowledge of another system in addition to the existing DCS.  PiControl’s advanced process control (APC) uses just the existing DCS and so the DCS engineer knowledge alone is adequate for the implementation and commissioning of PiControl’s advanced process control (APC).
  12. With time and updates, having an external computer for model predictive control (MPC, like DMC/RMPCT) means you have to upgrade operating system at regular periods and make sure anti-virus updates and Windows patches are being implemented.  PiControl advanced process control (APC) creates no such extra work, time and costs as all advanced process control (APC) is directly inside the DCS without need for external computer.

With the DCS-based approach, the advanced process control (APC) will be robust, compact and self-contained.  PiControl’s advanced process control (APC) design approach is faster, cheaper, require less maintenance and will not be black-box like model predictive control (MPC, like DMC/RMPCT) but can be understood and maintained far more easily.

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