Why Time Delay Matters | Control Systems in Practice

Time delays are inherent to dynamic systems. If you’re building a controller for a dynamic system, it’s going to have to account for delay in some way.
Time-Delay Systems: Analysis and Design with MATLAB and Simulink: bit.ly/2C354yp
Time delays exist in two varieties: signal distorting delays, like phase lag, in which each frequency is delayed by a different amount of time, resulting in a distorted signal shape; and non-distorting transport delays, in which the entire signal is postponed by the same amount of time.
Phase lag and transport delays are introduced into the system through a number of different components and processes, and understanding how delay enters your system will help you figure out the best way to deal with it.
This video covers time delays, where they come from, and why they matter.
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[@BrianBDouglas]

Hi everyone, thanks for watching this video! If you have questions or comments you'd like me to see, please leave them on this comment so that I get notified. Cheers!

[@pocsgeza1711]

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[@BrianBDouglas]

Thanks! I hope you like what I have so far. I need to add more to the book ... I've been too busy with videos.

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[@onur2998]

I found the idea of getting a delay margin based on the simulation of the model very interesting, can you do something like that for the gain margin?

[@gangakm468]

The best possible way to explain concepts.. thanks for all amazing videos

[@hainesjw]

Thank you so much! I refer a small Junior level ECE course here because you do such a good job of explaining the effect of delays and how one can experimentally introduce delays to find delay margin... up until that point, the students have been given nice linear problems to evaluate... ;-)

[@mnada72]

Plus being a great lecture of control it's to me a symphony of concepts played in the ultimate harmonious level. 🎼🎵🎶🎵

[@alexandrpetrov1110]

thanks for ALL your videos! It is GREAT!

[@MattiaMarinelli]

Great video, I really liked that!

[@naveedrezaaghamohammadi4996]

Awesome video, thank you.

[@i-tsunwang8929]

Brilliant Video!!!

[@muhammadatif1696]

Thank you sir!

[@pullopirkko]

and you can convert that time delay stability margin to phase margin with the rads it is oscillating. Helpful when you dont know the tf for the process. Gain margin can also be found with a gain block

[@makimak882]

Great video. Let's say there is a filler, this puts unstable volume bulk (approx 1.5% variation that oscillates in time vs targeted value) into box and takes its 12 cycles of machine to weight it. The problem is delay and how to correct box weight through change +/- of the filter capacity with that long delay. The system is trying to correct itself like in the car approaching corner example, is there any solution how to solve it to gain system stability around expected range?

[@power-max]

Yes, an explanation of my futile attempts and instability of setting the temperature of my shower every morning! 🛁 🚿 💦 🥵 🥶 🥵 🥶 🥵 🥶 💀

[@amirhosseindavazdahemami7268]

thank u so much

[@petrutarabuta5617]

Thanks!

[@kamleshvaghela3195]

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[@virtual_travler]

Jewel

[@pahvalrehljkov]

im so dumb ill need to watch this whole series 15 times... i just wanted to flatten my temp and humidity curve in my environment controller, now im using matlab, reading scientific papers on pid algoritms, i wish i was hippie sometimes...

[@johnlee746]

Why a negative phase margin means a system is unstable?

[@carultch]

It's specifically a system that crosses the point of an open loop gain equal to -1, or more negative than -1, that makes a system go unstable. This turns negative feedback into positive feedback, which exacerbates the error instead of correcting the error.
A negative phase margin means at the point where the gain crosses over unity, you have a phase that also has already crossed over a full reversal (i.e. 180 degrees), and this causes the transfer function to turn into -1 at the problematic frequency. Phase margin is how much phase delay you have remaining, before your system hits this point. So a negative phase margin, means you've already crossed the forbidden -1 value of your transfer function.

[@lucaspino8704]

3:12

[@francescoindolfo]

What is the difference between time delay and phase shift??

[@carultch]

Time delay means it is a uniform number of seconds of delay, regardless of the frequency. Phase shift means the time delay is a function of the frequency, rather than a fixed constant. For instance, a phase delay of pi/4, means a phase shift of 1/8 of a period, regardless of the frequency, such that at 10 Hz this corresponds to 1/80 seconds, and at 100 Hz this corresponds to 1/800 seconds. Whereas a time delay of 10 ms, will be a time delay of 10 ms at every frequency.