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Створити нову тему Відповісти  [ 17 повідомлень ]  На сторінку 1, 2  Далі
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 Тема повідомлення: Tuning PID control loops for fast response
ПовідомленняДодано: 08 серпня 2014, 23:29 
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З нами з: 29 листопада 2013, 17:11
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Tuning PID control loops for fast response
http://www.controleng.com/single-articl ... dc85c.html
Цитата:
When choosing a tuning strategy for a specific control loop, it is important to match the technique to the needs of that loop and the larger process. It is also important to have more than one approach in your repertoire, and the Cohen-Coon method can be a handy addition in the right situation.
The well-known Ziegler-Nichols tuning rules work well only on processes with very long time constants relative to their dead times, and on level control loops. However, its performance is not good on flow, liquid pressure, and many other loops that require fast adjustment. In contrast, the Cohen-Coon tuning rules work well on virtually all self-regulating processes and were designed to give a very fast response.
The method's original design resulted in loops with too much oscillatory response and consequently fell into disuse. However, with some modification, Cohen-Coon tuning rules proved their value for control loops that need to respond quickly while being much less prone to oscillations.


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 Тема повідомлення: Evolving PID tuning rules
ПовідомленняДодано: 18 серпня 2014, 17:12 
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Evolving PID tuning rules
http://www.controleng.com/single-articl ... b7cb8.html
A brief history, starting with the earliest PID controllers to the most recent developments. There is more continuity than you might expect.
Цитата:
Looking into the distant past of automation history, one can see the underlying concept of a PID controller exhibited in a nineteenth-century steam engine governor design, with the first real PID-type controller developed by Elmer Sperry in 1911. The first theoretical analysis of a PID controller was published by Nicolas Minorsky in 1922. His observations grew out of efforts to design automatic steering systems for the U.S. Navy. He realized that a helmsman controlled the ship based not only on the current error, but also on past error and current rate of change. Proportional control could provide stability against small disturbances, but it was insufficient for dealing with a steady disturbance, which required adding the integral term. Adding the derivative term further improved control. Currently, the basic principle is applied in many variations, but for our discussion we assume commonly used basic standard ISA PID controller in discrete form:

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 Тема повідомлення: Modern updates in PID control tuning
ПовідомленняДодано: 18 серпня 2014, 18:03 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Modern updates in PID control tuning
http://www.controleng.com/single-articl ... cb388.html
While PID control is often used because of its adaptability to a wide range of applications and operating conditions, there are several common problems that occur during the PID tuning process. Automatic and adaptive tuning can reduce the time and frustration often involved in reaching the correct tuning parameters for a given operation.
Цитата:
Proportional-integral-derivative (PID) control is the most common mathematical algorithm used to control automated systems in modern industrial and commercial applications. Essentially, the three parameters of proportional, integral, and derivative are gathered by a sensor and then used to adjust a control element that changes the output of the process to achieve a desired result. This loop feedback mechanism can be applied to simple processes such as controlling the temperature of a home with a thermostat or to very sophisticated applications such as flying by wire in an aircraft.

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 Тема повідомлення: Auto-Tuning Control Using Ziegler-Nichols
ПовідомленняДодано: 19 серпня 2014, 18:10 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Auto-Tuning Control Using Ziegler-Nichols
John “Zeke” Ziegler and Nathaniel Nichols may not have invented the proportional-integral-derivative (PID) controller, but their famous loop tuning techniques helped make the PID algorithm the most popular of all feedback control strategies used in industrial applications. The Ziegler-Nichols tuning techniques, first published in 1942, are still widely used today.
http://www.controleng.com/single-articl ... 49ece.html
Цитата:
John “Zeke” Ziegler and Nathaniel Nichols may not have invented the proportional-integral-derivative (PID) controller, but their famous loop tuning techniques helped make the PID algorithm the most popular of all feedback control strategies used in industrial applications. The Ziegler-Nichols tuning techniques, first published in 1942, are still widely used today.
Then, as now, the point of “tuning” a PID loop is to adjust how aggressively the controller reacts to errors between the measured process variable and desired setpoint. If the controlled process happens to be relatively sluggish, the PID algorithm can be configured to take immediate and dramatic actions whenever a random disturbance changes the process variable or an operator changes the setpoint.
Conversely, if the process is particularly sensitive to the actuators that the controller is using to manipulate the process variable, then the PID algorithm must apply more conservative corrective efforts over a longer period. The essence of loop tuning is identifying just how dramatically the process reacts to the controller’s efforts and how aggressive the PID algorithm can afford to be as it tries to eliminate errors.
Ziegler and Nichols proposed a two-step method for tuning a loop. They devised a test for quantifying behavior of a process in terms of how fast and how much the process variable changes when the control effort changes. They also developed a set of empirical formulas for translating results of those tests into appropriate performance settings or tuning parameters for the controller. Ziegler and Nichols actually proposed two such techniques, both of which are described in “Loop Tuning Fundamentals,” Control Engineering , July 2003.

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http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document


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 Тема повідомлення: Fundamentals of Self-Tuning Control
ПовідомленняДодано: 21 серпня 2014, 19:13 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Fundamentals of Self-Tuning Control
http://www.controleng.com/single-articl ... b6783.html
http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
Although proportional-integral-derivative controllers or “PID loops” have been the de facto standard of industrial feedback control for more than 65 years, they’re not always easy to use. For PID loops to perform up to their potential, they must first be tuned to fit each application, then periodically re-tuned to maintain the desired closed-loop behavior.
“Auto-tuning” controllers can help by automatically generating suitable tuning parameters upon request. With the control function disabled, the operator need only press the “tune” button and watch as the controller’s tuning function exercises the process until enough input/output data are available to quantify the process’s natural behavior.

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 Тема повідомлення: Applications of Self-tuning Control/Применение самонастраива
ПовідомленняДодано: 21 серпня 2014, 20:05 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Applications of Self-tuning Control

http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
Loop tuning is as much an art as it is a science. A well tuned feedback control loop can quickly and safely eliminate errors between the process variable and the setpoint, but endowing the controller with the necessary balance of aggression and patience requires a certain degree of skill and experience.
Fortunately, a variety of simple tuning techniques for proportional-integral-derivative (PID) loops have been automated and incorporated into commercial controllers. On-demand “autotuning” functions mimic the steps that a knowledgeable control engineer might take to tune a loop when it is first commissioned. On-the-fly “self-tuning” controllers also can continue to update their own tuning constants once the loop is fully operational.
Though both approaches have gained some degree of acceptance among industrial process control users, on-demand auto-tuning has proven to be the more popular of the two. Peter Wellstead is SFI research professor of systems biology at the Hamilton Institute, Ireland, and co-author of the chapter “Self-tuning controllers” in the fourth edition of the Instrument Engineers Handbook (Béla G. Lipták, ed, CRC press, 2006). He explains: “I did do a lot of work on self-tuning controller theory and worked on some commercial self-tuning products in the ‘80s and early ‘90s. After this, self-tuning went mainstream.” Many controllers have them as standard features now.

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Применение самонастраивающихся регуляторов
http://www.controlengrussia.com/innovat ... uljatorov/
Цитата:
Настройку контура управления во многих отношениях следует рассматривать как науку и как искусство. Хорошо настроенный контур управления с обратной связью может быстро и безопасно устранить расхождение между технологическим параметром и уставкой, однако установление в контроллере необходимого баланса между скоростью выхода на задание и мягкостью работы требует определенного умения и опыта.


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 Тема повідомлення: Is Automated PID Tuning Dependable?
ПовідомленняДодано: 24 серпня 2014, 23:49 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Is Automated PID Tuning Dependable?
Why do so many PID loops run in manual? One reason could be that automated tuning is no guarantee of success.
http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
It is surprising that more than 30% of all factory PID control loops are operating in manual rather than automatic mode. To make matters worse, of those loops operating in automatic mode, 65% produce less variance when in manual. This reality is possibly due to a dearth of personnel having sufficient know-how to tune and optimize a PID loop, which is one reason so many vendors provide automated configuration features. Unfortunately, these are all not created equal, and utilities from various vendors provide much different results. We will describe these features in the context of temperature control units, with the results of a performance comparison between several anonymous vendors.
There are two levels of sophistication in this technology, commonly referred to as auto-tune and adaptive-tune (or continuous tune). Autotune is generally offered as a standard feature and relies on characterizing the system through artificial manipulation of control output power levels. however, this is generally impractical to do during production operation. The software watches the process and analyzes its response while applying either a step increase in fixed power level, or cycle-tune using oscillating power levels. The step-tune approach performs best when started from a stable, constant process. The cycletune is not as dependent on initial conditions, but the process must be able to handle the amplitude of the necessary oscillations.
Adaptive-tune generally implies an increase in cost and requires more intelligence built into the controller. It must be able to monitor the process during production operation and judge when and how to modify PID parameters to maintain stability as conditions require. It characterizes the process without having to manipulate power levels artificially, as is done in both step and cycle style auto tune.
These capabilities reduce puzzling over PID parameters. A user can just let the controller tune itself. However, the ability of major vendors to deliver satisfactory control after tuning, however, was the topic of our recent investigation. The findings may shed light on reports of unacceptably poor performance found industry-wide.

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 Тема повідомлення: Relay Method Automates PID Loop Tuning
ПовідомленняДодано: 26 серпня 2014, 22:44 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Relay Method Automates PID Loop Tuning
A traditional loop tuning technique has been modified to simplify its implementation.
http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
Aproportional-integral-derivative (PID) controller operating in a feedback loop can be very effective at driving a measured process variable towards a desired setpoint, but only if the controller is adjusted or tuned to accommodate the behavior of the controlled process. For a PID controller using the ISA standard form of the PID formula, tuning is a matter of selecting appropriate values for the tuning parameters P, TI , and TD shown in the formula to the right.
Like all PID formulas, the ISA standard form computes the error between the process variable and setpoint as well as the integral and derivative of that error. It then weights the proportional term by a factor of P, the integral term by a factor of P/TI , and the derivative term by a factor of P·TD where P is the controller gain, TI is the integral time, and T is the derivative time.

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 Тема повідомлення: Tuning Thermal PID Loops
ПовідомленняДодано: 09 вересня 2014, 22:35 
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З нами з: 29 листопада 2013, 17:11
Повідомлення: 4990
Tuning Thermal PID Loops
When dealing with critical temperature applications, PID controllers are a common regulatory approach, but tuning these often requires a different strategy than other types of loops. Auto-tuning features can help if you understand them.
http://e-ditionsbyfry.com/Olive/ODE/CTL ... w=document
Цитата:
If you are responsible for working with PID temperature controllers, you have probably already discovered that such loops can be challenging and that the needs of a given controller and application can vary widely. This discussion is intended to help explain how these controllers work and to offer some basic guidance on dealing with a PID temperature controller. We’ve done our best to avoid unnecessary jargon while providing basic terminology and definitions that will be helpful when referencing controller manuals and other sources. Bear in mind, though, that controllers vary and applications vary, and we would be remiss if we lead you to believe that our experiences cover all cases or that our advice never goes wrong. Please be careful to consider the unique circumstances of your application as you implement any changes.

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 Тема повідомлення: PID auto-tuning using new model reduction method and explici
ПовідомленняДодано: 24 вересня 2014, 10:05 
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З нами з: 29 листопада 2013, 17:11
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PID auto-tuning using new model reduction method and explicit PID tuning rule for a fractional order plus time delay model
Journal of Process Control 24 (2014) 113–128
link
Цитата:
In this paper, a new model reduction method and an explicit PID tuning rule for the purpose of PID auto-tuning on the basis of a fractional order plus time delay model are proposed. The model reduction method directly fits the fractional order plus time delay model to frequency response data by solving a simple single-variable optimization problem. In addition, the optimal tuning parameters of the PID controller are obtained by solving the Integral of the Time weighted Absolute Error (ITAE) minimization problem and then, the proposed PID tuning rule in the form of an explicit formula is developed by fitting the parameters of the formula to the obtained optimal tuning parameters. The proposed tuning method provides almost the same performance as the optimal tuning parameters. Simulation study confirms that the auto-tuning strategy based on the proposed model reduction method and the PID tuning rule can successfully incorporate various types of process dynamics.


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