Anyone here study Control Theory?

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zombiess   100 MW

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Anyone here study Control Theory?

Post by zombiess » May 11 2015 12:27am

Just wondering if we have any control theory people here. I haven't met anyone who knows it yet, in real life or online. I've been studying it since November and it's finally starting to click. It's not the most straight forward subject. I have learned how to do some tuning of PID loops with the help of Matlab. I'm not a pro, but I've been able to get some stuff I've been working on tuned pretty well, including a cascaded PI loop which can be quite challenging.

I'm currently trying to process the root locus method to assist with studying the math and system stability.

So has anyone else visited the world of control theory here? It's an amazing subject. It's possible to perform all kinds of cool tricks with this skill. Building a box that can perform an automatic wheelie while a control loop that compensates for disturbances such as weight shift while maintaining a set angle becomes a reality. I'm after bigger fish though, but I'll probably circle back around to the auto wheelie idea in the future. Only so many hours in a day to do what we enjoy.

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Grinhill   10 kW

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Re: Anyone here study Control Theory?

Post by Grinhill » May 11 2015 3:42am

I studied control theory at university about thirty years ago, then did some real-world applications in the water treatment industry a few years after that.

The majority of jobs could be done with your basic PID (we used Programmable Logic Controllers which had a built-in PID function), but there were a few more complex ones as well.

One that I recall was doing pressure control in a large water main with a valve actuator that was probably too slow for the job. I found that the best way to get it to work was to deliberately add a time lag to the downstream pressure feedback signal. At first it may seem counter-intuitive, that it would make it even worse, but it effectively stops the controller from trying to make a new decision until the previous one has had time to have an effect on the system. So in that case, the book-learnin paid off. :)

The most recent occasion that the background knowledge proved useful for me was tuning power control on a Cycle Analyst V3.
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d8veh   100 GW

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Re: Anyone here study Control Theory?

Post by d8veh » May 11 2015 5:03am

I studied it way back in 1974 before we had computers to do the calculations. We had to solve problems with third order differential equations that took ages to work through. The one thing I can remember, and have used since then, is adding negative feedback nto the control signal to make the control system more stable. 40 years is a long time. I guess it's a lot easier now with computers, or you can do a lot more to make it complicated again.

It brings back a memory. We did an experiment in frequency response. We had a one ton RSJ hooked up to a hydraulic ram like a see-saw and we had to study what happened at different frequencies and different wave shapes. After the experiment we started playing - seeing how fast it would go, etc. We put a square wave into it and nearly shook the building down. Finally somebody turned the frequency right down to about .0001 Hz on the square wave setting, so it became motionless. I forgot about it and was sitting on it while we had a chat. A few minutes later I jumped off and it immediadely went ker-jonk. I reckon I was about half a second away from having my spine shortened by two feet. No health and safety in those days! I can remember our tutor would never tell us how to connect up the equipment. He said, "If you're engineers, you should be able to figure it out for yourself".

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Lebowski   1 GW

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Re: Anyone here study Control Theory?

Post by Lebowski » May 11 2015 6:02am

Me :D at university 20 years ago. Still use it quite a lot. The control loops in the controller IC are not your bog standard PID by the way :mrgreen:

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