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Instrument Engineers' Handbook
Process Software and Digital Networks
Bela G. Liptak, Editor-in-Chief
Instrument Engineers' Handbook is often referred to as the "Bible" by the Industrial Automation professionals. Its Volume 3: Process Software and Digital Networks, 4th Edition includes many innovative and exciting technologies and software products such as Model-Free Adaptive (MFA) control developed by CyboSoft, General Cybernation Group Inc. You can order this book from CRC, Amazon, ISA, or other book stores.
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The following are sample pages from Chapter 26, "Model-Free Adaptive Control Software" of this book.
MFA Control Approach
The MFA control approach overcomes the major weaknesses of PID and MBC in the following ways:
1. PID is basically a “one-algorithm-fits-all” method. Inevitably, its capability is limited. In other words, PID is more like a general-purpose medicine. Except, there is no way for one medicine to effectively cure all illnesses.
2. Model-based control (MBC) is more like a “one-algorithm-fits-one-system” method. If the process dynamics do not change frequently and the process model can be well maintained, MBC can provide good performance. However, since it is so specialized and has a potentially high installation and maintenance cost, large deployment may be difficult.
3. MFA control takes a “one-algorithm-solves-one-problem” approach. Each MFA controller is designed to solve a difficult control problem while neither process model nor identification is required. For instance, the Nonlinear MFA controller can control various types of extremely nonlinear processes in different industries and applications. Each MFA controller is like a specifically developed medicine to cure one specific ailment. Therefore, large deployment is possible. This design philosophy is based on the Combined Intelligence MFA Methodology that is presented in the last part of this chapter. We will also present several application case studies to show solutions to difficult control problems using MFA.
MFA Advantages and Suitability
Every technology and method have their advantages and suitability. So do PID, MBC, and MFA. Figure 26.2 illustrates the suitability of PID, MFA, and MBC. PID is a controller for a large variety of processes where no detailed process information is required (Black Box). However, since PID is a fixed controller, it cannot deal with process dynamic changes. The MBC is well suited for controlling a process where detailed knowledge is available (White Box). For instance, when an airplane is designed, its mathematical models can be obtained. So, a perfect control system can be designed using model-based methods to control the airplane. MFA is suitable for controlling processes with qualitative process knowledge but no detailed process models are available (Gray Box). In addition, the process dynamics can have significant variations. Many industrial processes are gray boxes that have frequent load, fuel, and dynamic changes.
Fig. 26.2
Suitability of different control methods.
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