MFA Control Methodology

"All roads lead to Rome." A problem usually has multiple solutions, and a process can usually be controlled using different controllers based on different control methods. Almost every control method has its merits and weaknesses. What's important is to use the right controller to fit the application at a minimum cost.

In natural science, the combination of physics, mathematics, and philosophy plays an integral part in developing a theory that is practically useful. Physics is the foundation for the study of the physical process or environment; mathematics provides the tools to precisely describe the physical process or phenomenon; and equally important is the philosophy that provides directions.

The development of Model-Free Adaptive control technology started from a simple desire to develop a new controller that could easily and effectively solve various industrial control problems. The actual development process has evolved from a prolonged interest in the study of Combined Intelligence methodology. Since Model-Free Adaptive control does not follow the traditional path of model-based adaptive control, the philosophy behind the Combined Intelligence has led the way up this long and rocky road.

Combined Intelligence Methodology

The Combined Intelligence Methodology developed by the author of this section consists of the following problem solving philosophy: (1) Always seek a simple solution for a complex problem; (2) Use all information available; (3) Do not depend on the information's accuracy; and (4) Apply a technique that fits the application. These four key points are described in the following.

Seek a Simple Solution

A simple solution is almost always the best solution. A complex solution might achieve a little better result, but the cost can be very high. Most users want to have a tool or system that is easy to use, launch, and maintain with the best price-performance ratio. A simple solution usually fits this need well.

Use All Information Available

It is a cliché, but we are living in the information era. Information has value. A small piece of information can make all the difference. When solving a problem, do not waste the valuable information available. For instance, a process delay time can easily be seen from the process trend chart. A regular PID controller ignores this important piece of information.

Do Not Depend on the Information's Accuracy

All information received may not be accurate. What's worse is we might not know whether the information is accurate or not. If we knew, we would simply have the option to use or not use the information. For this reason, the solution has to be agile or adaptive enough to deal with the inaccuracy of the information and the uncertainties.

Apply a Technique That Fits the Application

Arguments often arise between people who believe in very different problem-solving methods. For instance, model-based and rule-based methods are two very distinctive approaches in control theory. Since almost all methods have their merits and shortcomings, why argue? Let's use the technique that fits the application.

The MFA Control Approach - A summary

To see how the MFA control method is developed based on the Combined Intelligence methodology, we will relate MFA to each one of the four key points.

Seek a Simple Solution

PID control is simple since it is a general-purpose controller and its algorithm is easy to understand. However, PID is almost too simplistic to control complex systems. In this regard, PID cannot be considered an effective solution to the more difficult control problems. On the other hand, model-based advanced control methods have proven themselves too complex to launch and maintain since they depend on either a first principle or an identification-based process model. A dream controller has to be powerful enough to control various complex processes yet simple enough to use, launch, and maintain. MFA is a solution that fits these requirements.

Use All Information Available

Model-Free Adaptive control, as its name suggests, is a control method that does not depend on either first principle or identification-based process models. However, we do try to use all the process information available. For this reason, it can be considered an information-based controller.

For instance, the process time constant defines how fast a dynamic system responds to its input. A slow process might have a 10-hour time constant and a fast process might have a 10-millisecond time constant. It would be unwise not to use this information for the controller. In addition, it is relatively easy to estimate the time constant by reading a trend chart. Other important yet easily obtained information about a process includes its acting type (either direct or reverse), static gain, and delay time, if any. An MFA controller is designed to use the process parameters that can be easily estimated.

Do Not Depend on the Information's Accuracy

A process can be classified as a white, gray, or black box. If its input-output relationship is clear, the process is a white box. We can easily use existing well-established control methods and tools to design a controller for this process.

When we are not sure if the process input-output relationship is accurate, or if the process has potential disturbances, dynamic changes, and uncertainties, the process is a gray box. In this case, MFA's adaptive capability is able to handle such changes and uncertainties. PID or model-based control methods will have a much tougher time or higher cost addressing these uncertainties.

Apply a Technique That Fits the Application

MFA is neither model-based nor rule-based. We might say that it is an information-based control method. If the argument is made that the process information used is equivalent to a process model, that's perfectly acceptable. The key to this approach is that we focus on delivering a simple, adaptive, and effective solution.

To extend this idea, a series of MFA controllers, many of which are described here, have been developed to address a variety of difficult control problems. Users can simply select the appropriate MFA, configure its parameters, launch the controller, and reap the benefits. With the proper approach, no manual tuning and maintenance is required.