PD2 Feedforward Control for Process Transfer Function with Damping = 0


To whom who is interested:
Page 1: Process transfer function with 'damping ~ 0'
Page 2: PD(PID) control, PID not active
Page 3: Math Model
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IT WORKS!
Reply to
JCH
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Dear Jan
JCH wrote:
I have been following the discussion here (passively) for quite some time and register you coming up with various new theoretical ideas that you claim are superior to the existing control design schemes. And yet you have troubles to gain recognition of a single person participating in this discussion.
May I have one suggestion? Why don't you follow a more standard route to the professional recognition that you struggle for? Put your ideas down to a paper, describing the notations properly, formulating the problem clearly and unambiguosly, explaining every detail of your proposed solution, not hiding anything, and submit it to some leading journal on control theory. As you appear to offer fundamentally new concepts, I can recommend one of the following leading journals on control theory:
IEEE Transactions on Automatic Control IFAC Automatica SIAM Journal on Control and Optimization Systems and Control Letters International Journal of Robust and Nonlinear Control International Journal of Adaptive Control and Signal Processing Optimal Control Applications and Methods European Journal of Control International Journal of Control
I can assure you that your paper will receive proper and unbiased attention by people who are experts in the field and whose books you studied (hopefully) from. Alternatively, you can consider either of the two journals
IEEE Transactions on Control Systems Technology IFAC Control Engineering Practice
which are a bit more practically oriented, and yet quite mathematically rigorous.
I believe that it is the only right way. I dont find the discussion group here the best place for a just evaluation of your results (of course, you can do whatever you like, we are free people, but the question of your motivation then arises). The reason is that the forum is attended by diverse audience, including beginers. I don't find it quite fair obviate the standard fields for competition with best in the field and to offer the results to newbies. On the other hand, it is well possible that your results deserve this appreciation by the community. But you will never ever receive it here, on anonymous internet discussion forum, in contrast with having your paper published and ARCHIVED by some leading journal. That is the only way to get these fancy labels of yours like PD2, PD3 into the popular textbooks.
Finally, let me explain the reason for my passivity in the discussion so far. Just imagine that a newcomer to the discussion here goes to the above link without spending several hours by reading your previous inputs here to learn your terminology and notation. Even though my full-time profession is reading and writing control theoretic texts, I have big troubles to find a formulation of the problem, to identify assumptions, to learn how you computed the particular values. I confess that this gives me an impression that you are not really interested in feedback and therefore I am not much motivated to work hard to understand what you are actually trying to do.
All the best,
Zdenek Hurak Department of Control Engineering Faculty of Electrical Engineering Czech Technical University in Prague
PS: Please note that most probably I will not have access to internet till the next Thursday and therefore excuse my lack of responsiveness (should there be anything to respond to).

Reply to
Zdenek Hurak
_____ I second Zdenek Hurak's above mentioned recommendations based on what i have seen of JCH's (in Germany) comments. I have offered the odd advice when a "Question about PI control integration time" arose on 2 June. It is very important to ensure that the problems are described clearly and completely, and that the solutions are fully documented.
In my professional opinion JCH might consider taking a position in an industrial setting and work on some real live process plants. There are plenty of real problems to solve; often very simple ones. There is no shortage of control algorithms in the literature, and some of the recent ones (like BrainWave from Vancouver, BC, Canada [now owned by an Austrian company]) and the multi-variable interacting control packages show a great deal of promise, and have been accepted by many plants. These newer approaches are now possible due to the vast processing power we have access to. Simulation has its place, but must be supported by a thorough understanding of the physical limits of process plants.
In my own control engineering career (with a very large multi-national oil/chemical company) i had the opportunity to develop computer control applications that ranged from simple furnace excess O2 control to multi-variable distillation and reactor controls. To learn the control discipline properly there is nothing like designing a control application, developing the economics, getting approval from the Superintendent of Operations, training the operators in the control room, and tuning the loops properly during the commissioning phase.
There is clearly room for academic work, and i fully endorse that as well. However, we must always keep sight of the ultimate goal of the discipline; improve the performance of processes (batch and continuous) via process control that is stable, rugges, reliable, and cost effective.
The technology employed must also be matched to the region of the world in which it is utilised. It may be inadvisable to use a sophisticated gas chromatograph based control scheme in a distillation train on a Venezuelan gas processing platform. The same scheme would be fine in Canada or the USA in a similar plant. The reasons have to do with availability of qualified technical personnel and the ability of local knowledge workers to maintain complex control systems.
Reply to
jch
What is your definition of damping = 0? I don't see how you figure the damping factor is zero given A1 is not 0.
That works on paper but what do you do when the model isn't exact?
So what is the relationship between K1 and K2? I have said before you should need a target generator and feed forwards for something so simple.
Ship it! Just kidding. Seriously, it only works on your website.
Again, there is no educational value to your website because you don't show how you calculate your solutions.
I think you should play a little game. I think you should vary the model using a standard deviation of 10% after you have calculated the gains and feed forwards. I do. This test lets you know how robust your solutions really are. Feed forwards are great but if they are off by 10% the PID must correct the control output by 10% to get the output to the true value.
Another test. Quantize your double precision floating point numbers to 3 decimal places to represent the the fact that AtoD converters quantize the feed back values.
Peter Nachtwey
Reply to
Peter Nachtwey
I'm just a bit stunned that so much analysis would be carried out on such simple systems. Where I come from the control engineer wouldn't even get to hear about these sorts of things. Any competent instrument tech would have it tuned and working fine by morning tea time. Use it as an exercise for one of the apprentices.
Reply to
Bruce Varley
"Peter Nachtwey" schrieb im Newsbeitrag news: snipped-for-privacy@n15g2000prd.googlegroups.com...
[...]
It works on my computer, not paper.
Show your alternative! The same conditions, please. Process tranfer function: v1 + A1*v1' + A2*v1'' = v2
A1 = 6.324E-05 A2 = 0.001
w scheme as shown in
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Reply to
JCH
_____ Exactly. Properly trained instrument technologists with some decent field experience should be able to solve a great percentage of the problems in the plant, especially tuning issues.
Reply to
jch
Ditto, but remember there's a lot of servo systems out there, too. Many of them that have never been close to a chemical plant since they were little plastic pellets waiting to be sold.
Reply to
Tim Wescott
snipped-for-privacy@n15g2000prd.googlegroups.com...
As usually you didn't answer my question about how you figure the damping =3D 0?
Peter Nachtwey
Reply to
Peter Nachtwey
snipped-for-privacy@n15g2000prd.googlegroups.com...
What is the relationship of k1 to k2?
Peter Nachtwey
Reply to
Peter Nachtwey
snipped-for-privacy@n15g2000prd.googlegroups.com...
Sorry, guys. I am asking short simple questions. One on each post. You can see that JCH somehow gets confused and never remembers to answer the questions. I am trying to keep it simple.
BTW, I think we are making progress. At least JCH isn't pushing his infinite gain controller anymore.
Peter Nachtwey
Reply to
Peter Nachtwey
"Peter Nachtwey" schrieb im Newsbeitrag news: snipped-for-privacy@a26g2000pre.googlegroups.com...
As usually you didn't answer my question about how you figure the damping = 0?
Jan:
Cited
Cited
Cited
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(now 6 pages of information)
Three times in text plus once as plot (~0)! Makes 4 times. Please, ask not any more for the damping value. It was known since my first post (page 1).
Instead I am interested in seeing your PID result I have asked for. If it looks worse don't feel ashamed. It can't be better.
Reply to
JCH
"Peter Nachtwey" schrieb im Newsbeitrag news: snipped-for-privacy@z28g2000prd.googlegroups.com...
What is the relationship of k1 to k2?
Jan:
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definitions for K1 and K2 in page 3
Reply to
JCH
"Peter Nachtwey" schrieb im Newsbeitrag news: snipped-for-privacy@i38g2000prf.googlegroups.com...
Sorry, guys. I am asking short simple questions. One on each post. You can see that JCH somehow gets confused and never remembers to answer the questions. I am trying to keep it simple.
Jan:
Thank you very much for keeping it simple, Peter.
Peter:
BTW, I think we are making progress. At least JCH isn't pushing his infinite gain controller anymore.
Jan:
Sorry, I do.
Definition and usage: Posted 2007/May/11
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Please, read again.
Reply to
JCH
: : "Peter Nachtwey" schrieb im Newsbeitrag : news: snipped-for-privacy@a26g2000pre.googlegroups.com... : : > "Peter Nachtwey" schrieb im : > Newsbeitragnews: snipped-for-privacy@n15g2000prd.googlegroups.com... : > : > [...] : > : > > That works on paper but what do you do when the model isn't exact? : > : > It works on my computer, not paper. : > : > Show your alternative! The same conditions, please. : > Process tranfer function: v1 + A1*v1' + A2*v1'' = v2 : > : > A1 = 6.324E-05 : > A2 = 0.001 : > : > w scheme as shown : > in
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> : > -- : > Regards/Grüße
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> Jan C. Hoffmann eMail aktuell: snipped-for-privacy@nospam.arcornews.de : > Microsoft-kompatibel/optimiert für IE7+OE7 : : : : As usually you didn't answer my question about how you figure the : damping = 0? : : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> : : Jan: : : Cited : > Page 1: Process transfer function with 'damping ~ 0' : : Cited : > A1 = 6.324E-05 : : Cited :
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d=0.001 (now 6 pages of information)
d=0.001 is better. It depends on your definition of close to 0 doesn't it? At least now I know you know what you are taking about when it comes to damping factors and aren't throwing out numbers. Showing your work would have answered this immediately.
: Instead I am interested in seeing your PID result I have asked for. If it : looks worse don't feel ashamed. It can't be better.
You just don't get it do you?. I have all of these problems worked out symbollically. I can just look at the response you have and pick a desired response that will be faster or smoother or better by any definition you like and the symbolic formulas will calculate gains to give me that response. It is easy on Mathcad or some other symbolic math package when you don't have to worry about reality. So what is you want or are trying to prove? If you want to win some contest you won't. If you want to know how to calculate gains I have shown you how I calcualate gains symbolically and using Ackermann's equation in previous threads but you have ignored it. You should know that what I have shown in the past is just two methods and there are others.
Peter Nachtwey
Reply to
Peter Nachtwey
: : : : What is the relationship of k1 to k2? : : : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> : : Jan: : :
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Exact definitions for K1 and K2 in page 3 : I see no definitions there.
On this page
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see a definition of k1=k2=1
This again is sloppy. It works but if one is looking to your website for an answer they would be in trouble. If k1 was any number other that 1 the equation would be wrong. The equation should read k2=1/k2. Actually, I wouldn't even bother with k2 and just define your feed fowards like this (u+B1*u'+B2*u''+B3*u''')/k1
You are still using the feed forward crutch. When you have perfect feed forward gains then the PID tuning doesn't matter much because there should be no error. I know you use the feed forwards will mask the error in your tuning. I don't need to use feed forwards just to get a faster critically damped response than yours. If you are really clever you will find that you can design your controller to have a response like 0.0009887008 u ' ' + 0.0601797 u ' + u = w Then you will find feed fowards are not necessay for response to step changes in the set point.
Peter Nachtwey
Reply to
Peter Nachtwey
"Peter Nachtwey" schrieb im Newsbeitrag news:9Y-dnSXVCYagw_HbnZ2dnUVZ snipped-for-privacy@comcast.com...
Sorry, you are on the wrong page. The task I refered to is
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definitions for K1 and K2 in page 3
Reply to
JCH
"Peter Nachtwey" schrieb im Newsbeitrag news:m4mdnS_JVO0wxvHbnZ2dnUVZ snipped-for-privacy@comcast.com...
Peter, please read my work again: 2007/June/08
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task was clear.
Show us a hardcopy with few points calculated or a plot. I already compared PID and PD2(PID). Result: PD2(PID) is better.
I will know which method is better. I truly couldn't find that just PID is better. I had had a contest already with me, i.e. PID against PD2(PID). By the way have you also tried controlling with disturbance.
Sorry Peter, do relate to the task. You know damping is almost zero. It's a bit more difficult.
Actual task to discuss:
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Reply to
JCH
: Peter, please read my work again: 2007/June/08 :
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The task was clear.
: : > : Instead I am interested in seeing your PID result I have asked for. If : > it Why should I? You haven't shown how you calculate your PID gains once. I have shown how I calculate gains twice, once symbolically and once using Ackermann's method. In both cases I can just increase the desired response until it beats yours. This is easy when I don't need to worry about reality.
BTW, you don't know how funny your PID vs PD2(PID) comparison is. Do you play chess with yourself too? You can prove any opening is better than another because your personal biases will get in the way.
Peter Nachtwey
Reply to
Peter Nachtwey
"Peter Nachtwey" schrieb im Newsbeitrag news:j7GdncXLgtKhSvHbnZ2dnUVZ snipped-for-privacy@comcast.com...
Ok, please give us the K_PID, T_I, and T_D you symbolically found as best.
Refer only to this thread:
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I show you the plots/comparisons.
Note You should know that any plot is a result of the formulae you find in page 3.
Reply to
JCH

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