Nyquist Stability Criterion, Part 2
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An explanation of the Nyquist Stability Criterion part 2. This video steps through the how to sketch a Nyquist plot by hand, what to do if there are open loop pools on the imaginary axis, and goes through a example showing the benefit of Nyquist over Bode plots.
Errata:
Links:
Check out nyqlog.m from the mathworks website.
www.mathworks.com/matlabcentra...
Professor Gopal explaining how to do a rough sketch of the Nyquist plot: Starts at 17:15.
• Lec-36 The Nyquist Sta...
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Brian Douglas you are a HERO.
I am an Engineering student in Belgium, I followed the course Control System Engineering (CSE) in Bachelor and Master year. In the Master I had no idea what the purpose of this course was, I did not understand why the professor was making strange drawings in the S-plane all the time.
Then finally I found your video lectures. I have watched your full playlist.
You inspired me to like CSE. You understand how the brain wants to study. You explain the purpose of each subject, you make drawings, you use different colours, you talk fast so we can train our brains to think faster, and if it is going to fast we can pause and replay.
I really enjoyed your lectures. This will definately make me a better engineer.
Yesterday I aced the Exam of Control System Engineering.
Thank you very much!
I wish you the best in life, and I hope you will continue your purpose to help engineers from all over the world.
Hehe, second bachelor year engineer here, in exactly the same situation. You went to Leuven?
x3 here! Leuven salutes you Brian
It's good but speaking so fast! These topics are new for me so subtitles (not a native speaker) and pauses are helping me :)
As a mech student, i constantly think to myself, what would i do without you mr. douglas
us mech students owe you big time man
I'm having control system exam tomorrow and I came to this channel because I didn't attend the classes of the same professor you are referring to here "Prof. Madan Gopal" ...lol
You're lucky then. Are you in SNU?
Brian Douglas - A man who puts in his time and effort to help electrical engineering students from all around the globe. Not all heroes wear capes, some just explain electrical engineering concepts.
You're the only reason I passed my Dynamics of Systems and Controls class. THANK YOU!!!!
I hope every engineering class could be like this. You just solved my doubts in less than 20 minutes. Heartfully thank you sir
I love your explanations Brian. You explain the theory but importantly you also put the theory in a context that makes sense to an engineering student. You convey to the viewer the big picture of how the theory is used to solve real world and meaningful problems! Thank you.
The 3 possibilities:
1.- The -1 does not get circled; the system is stable if there are no poles in the RHP.
2.- The -1 gets circled one or more times in a CCW direction; the system is stable if the # of times it gets circled is equal to the # of poles in the RHP.
3.- The -1 gets circled one or more times in a CW direction; the system is unstable.
Sir, you deserve a medal, this is exactly what I was looking for!!!!!
Asterio I'm glad it was helpful :)
great summary ! Sir.
I have a question of this video:
at 12:11, the gain on the w plane should be undefined, since the magnitude of zero phasor ( no zero for 1/s ) is also 0. According to the definition at 4:18.
brian got the assist but you fuckin slam dunked this shit.
you're a fucken legend
You have put a lot of work into these with resulting clarity, perfect pace and additional resources made available. Thank you!
This video is pure gold. It helped me understand something that my course material couldn't in 25 pages. I finally am getting a grasp on system control! If I pass this exam it is due to your videos, so extremely helpful.
The way you explain is awesome. I have been relying on your videos to pass all the quizzes and assignments in present semester. I would be very thankful if you can upload the part 3 of Nyquist Stability Criterion which explains gain and phase margin.... Your efforts are highly appreciated. Thank you :)
To clarify; if a zero (not a pole) is in the RHP the system is unstable, because the Transfer Function we're evaluating is actually the Denominator of the ACTUAL Transfer Function we're determining stability on. (GH is open loop, but X / (1+GH) is close loop). Nyquist difference between GH and 1+GH is just a shift of -1, so we evaluate GH as though its our transfer function, when in reality we're evaluating the Denominator of the transfer function. So what indicates stability, and what indicates instability, is flipped.
I.E. a pole creates a denominator of infinity, which is stable, while a zero creates a denominator of zero, which is unstable for the full thing.
Just wanted to help make that clear for anyone that missed it.
B Moore Thanks for adding this clarification!
B Moore
+Brian Douglas Mister Douglas I wanted to ask that in the last minute you said that there is one pole in the right half plane and two clockwise encirclement's of -1 so there are three poles in the right half plane. But in the previous lecture you said this Z=N+P. That clockwise rotation plus poles is equal to zeros in the right half plane. So which one is it? I am confused.
I believe this formula Z = N + P finds how many open loop (GH) zeros exceeds the open loop poles in the RHP, if the contour is CW. (If the contour was CCW it would be how many open loop poles exceeds the open loop zeros in the RHP of the s-plane). In this case N=2, so we know we have 2 open loop zeros more than poles in the RHP.
But since the open loop tranfer function is in the denominator of the closed loop transfer function G/(1+GH), this open loop zeros we found in excess are related to the poles of the closed loop TF. He showed in MATLAB that there is one unstable open loop pole, so in the end of the day the formula says that apart from that 1 unstable open loop pole, we will have more 2 (=N) unstable closed loop poles, so a total of 3.
Please comment if I said something wrong...
hbaqueiro you might be right. But I already gave my exam and I nearly passed my course. But thanks for the reply!
You're awesome, I learned in 19 minutes what my teachers couldn't explain me in 1 semester!
You have no idea how much you've helped me this semester! Thank you for the time and the work you put into these videos to help everyone around the world! 🤩🤩
Brian! you are savior...
I`m Electrical Engineering student in Pakistan. Our professor for the course 'Feedback and Control Systems' recommended this video in his lecture. I`m totally in love with the way you explained such difficult topics. Keep doing the good work.
HATS OFF 🙌🙌🙌
Also a mechanical engineer here!! You are really a life saver and an excellent lecturer! it's really helpful for students like me that this subject is just something you should know a little about. You really make it funny! THANKS
thank you so much Brian, you are a perfect teacher, i feel sad that i did not found your videos in the beginning of the semester. wish you the best, you are number one!
You are really a gift. This is the most understood and sensible illustration of the criterion. Go on!
I had the biggest eureka moment at 13:45, I can't thank you enough for this!
the same for me here
I just want to say that, if I pass my exam tomorrow, it will most definitely be because of you! You explain 10x better than my teacher, thank you so much for putting your time into making these videos! Subscribed ;)
I imagine how many enginnering students just passed in control systems engineering class
I dont pass classes I pass away
Lol I have backlog ....I have to give Control system exam next month 😭😭😭😭😭
It's too tough and complex
Watching the video at a half speed made everything more clear :) You are an awesome professor.
Thanking you from the bottom of my Heart for sharing all these in detailed insights about Nyquist Plot. Just a big fan of your lectures.
You Rock!
Great video... both part 1 and part 2 really helped me get a clear understanding of the concept. and the fighter jet example in the end was awesome.
Love to see people from outside of india also watch NPTEL videos and not just us college students; that's the love for engineering i guess.
I am also studying engineering and I have a funny story for you Brian.
The other day, when finishing the automatics and controls course, the professor said: "If somebody did not understand something I have been explaining this last weeks during hours of lectures, you can search a guy named Brian Douglas in youtube and he will explain it in a few minutes with his videos. Have nice holidays". -- True story.
You have reached universities professors! Keep on!! Incredible videos. Lots of information explained clearly and quickly. Thank you for your amazing work!
That's pretty awesome! Thanks for sharing.
you've taught me all these concepts within an hour what my professors couldn't teach me in 5 lectures
Believe me, you are the best among all the professor that I've seen
Dude this is video was so helpful. Thanks alot.
The concept was taught so much better than our teacher at university.
BRILLIANT example.... Thanks so much. Last video left me itching for an explanation on why bode plots don't help with unstable systems. This gave me some insight into that atleast.
Brilliant explanation, a lot better than my professor, great job!
Thank you Brian, this saved me a lot of reading (and confusion)!
Fantastic lectures about the Nyquist Criterion. I am a student of the Engineering Physics programme at the Royal Institute of Technology in Sweden. Signed up to your channel and will be following your channel.
I am doing the undergraduate course of Control Theory right now.
Im mechanical engineering (structure and material) student from Malaysia. I really hate this control system because i dont know anything what lecturer teach about ! Then, when i see your lecture on this video, its interesting subject actually !! you are great lecturer ! Thanks sir!!
Passed my exam, thank you so much Brian!
Congratulations! That's a good way to close out the year.
Awesome lessons! its so easy to understand the way you teach it
Thanks for the video Sir. It really helped me understand this difficult concept. Such exceptional clarity of A/V. Sharing and recommending this.
this video really helped me in understanding nyquist... i really didn't quite get it from the lecture at the university.. but it was really made simple here. thanks a ton~! :)
man....i regret not finding this channel earlier
A very intense and tiring lesson, 18 minutes but actually 2 hours... Thanks for labour.
You left me amazed and speechless 🤐 , thanks alot.
Awesome video, Brian. And a personal thanks for the email assistance. Hopefully I'll do well in the exam!
Thank you for making great video! from Korea.
Thanks man, I was really got deprressed understanding Nyquist criterion and root locus. But it is easy, thanks to you ;).
THESE VIDEOS ARE GOLD BRIAN !!!!
Thank you so much! This makes so much more sense now.
Thanks Brian, you're a legend. How would you handle and draw the contour of systems with deadtime?
i have to say you are the reason i passed my firswt test . lets hope you can make me pass the second one . thx and keep the good work
these videos ares much better than my professor and all my textbooks combined
I go to a top 10 school and you teach it better than my professor.
Dude (Brian Douglas) do you know how many undergraduate lives you are saving by uploading these amazing videos. You are like Mother Teresa but with balls. I read the book but it takes so long to make sense of it....this is it man this is it!!!
Just Amazing !! :D You're an amazing teacher !
Dude,
you rock I can now finish my feedback controls hwk!!!
Thanks for the video very helpful, do you have a video on relative stability( gain and phase margins) using nyquist and bode plots?
Amazing job as usual! Keep it up Brian and thanks!
Hi Brian, I love your videos! It would be really cool to see your whole screen in a PDF or similar format, just to be able to see it all at once.
Hi Brian, thanks for your video. I wonder whether we could figure out gain margin and phase margin from the Nyquist plot?
Great lecture man! Saved my day!
Thank you so much! Your videos are so clear :D
Bro,that helped like everything.Thank you so much,the way video is presented is really cool,i owe you this one,subscribed. :)
Damn you make me feel all my graduate school tuition is in vain! Actually, your demonstration is waaaay better than most professional professors, huge THANX!!
Fantastic! cannot wait for another one!
Thank you so much for these videos!
Couldn't be crearer man!. awsome work!. excellent teaching
Hi Brian, Thanks for the videos :) Appreciate it. Can you point me to few other examples where Nyquist plot shows the system is unstable while Bode says it's stable? I am interested in analyzing such systems. Thanks for your time and effort!
Thank you man ,good explanation.
You deserve more than 10 million likes...
14:12 *The closed-loop system is stable since no open-loop "ZEROS" in the RHP, Am I right? because the zeros of 1+GH are the poles for the closed-loop G/(1+GH).
I love everything about your videos and I can't thank you enough for your help in my control systems course. I have just a small comment on the sound of them howerver: usually I listen to them with headphones, and I've noticed that sometimes the sound is a bit biased towards one ear (usually the right hand one). One example would be the video of stability margin, number 17 in your video. Also the sound level sometimes differ between your videos, which is slightly annoying when going through a playlist. Minor things really, but if you cold make the sound mono and level the sound to a specified level you would really reach perfection.
Thanks again!
Please check the examples in my channel as well and let me know if you have any feedback.
Great video. I really appreciate your time.
Hi Brian, love your videos! I was wondering if you could briefly explain the main application difference between Nyquist plots and root locus plots. e.g., say you're designing a PID controller and want to fine-tune the gains to stabilize your system, are there certain cases where one might be advantageous over the other? Thanks!
thanks brain, u have done great job, it was really helps me to do my exam well :)
Thanks for the video, it really helped!
Great work Brian!!. . .I wish I would have found you last semester.
Is it possible for you to cover state space models??
I laughed when I heard you say "if you'd like to hear it from a professional professor", I'm here because my 'professional professor' did a terrible job explaining it and you're actually better. I'm sure Prof Gopal is great but I'll take your simple explainations anyday
You are great! Thank you very much for these videos!
These videos have been brilliant. Is there a part 3 to the Nyquist series? Gain and phase margins are mentioned as being in the next video - can't find any indication there is a next video.
Excellent! Please keep adding videos :) for example digital control
How does the relativity of the open loop transfer function (i.e, n-m) affect the phase of the Nyquist Plot?
thanks mr.Douglas ! i m korean student majored in Control . this video is very helpful to me to study Control theorem easily. :-)
As Always ...The Legend Douglas.
please upload gain and phase margin video.....
great explanation. thanks Douglas
Thankyou you give very good Excellent instructions.
Hey, thanks! this has been SO helpful.
I have one question: what happens if the number of poles in w=0 is more than one? i.e. 1/(s^3)
Awesome explanation ! Thanks a lot!
Amazing. I will be buying your book
thanks Brian, it was very helpful :)
THANKS! Is the number of closed loop unstable poles = number of encirclements of -1 + number of open loop unstable poles?
Hello. When you were discussing the case of strictly proper transfer function, you said the phase of the origin in the w-plane doesn't matter. But when jw sweeps from positive infinity to negative infinity in the s-plane, the phase in the w-plane seems to sweep from negative pi to positive pi. If that's the case, shouldn't the same loop around trick also be done at the origin in the w-plane for more rigorous mapping, cause sweeping around the origin maps to sweeping around +/- infinity jw correspondingly in both planes? Thanks.
can you clarify that last example? surely if there are two clockwise encirclements of -1, that means 2 zeros or 2 more zeros than poles in the nyquist plot? And since we know there is one open loop unstable pole in the RHP, then there are 3 zeros in the RHP... were did the 3 unstable closed loop poles come from?
Appreciate your efforts.
Great Vedio !
I was wondering what was the use of nyquist plot until you gave the F16 example.
Thanks a lot, could score on Root locus, Bode Plot, Nyquist plot which constituted 30 marks out of 50 for my end sems
Come teach at my university and I might actually choose to study control systems next year.
thanks alot for this helppful leactur , its realy help me teaching this subjects
Hi Brian, can you please tell which software and hardware you use for making these animation 😀. It would be great help.
This is the better explanation I found on the Internet about Nyquist criterion(I viewed also the explanation of the indian professor you suggested). But there’s problem that I’m not able to solve: the only calculations that we do with the transfer function to plot it, is to consider it restricted to s value j-omega from j-zero to j-plus infinity... but: how can we be sure that the Nyquist contour is the one that include the right half plane (and not instead, the left half plane)? If we draw the contour of the left half plane we arrive to the same conclusion about the route from j-zero to j-plus infinity. Do you have the answer to this “tricky” question? Thanks.
You are fucking awesome. Really you should teach everybody how to be a teacher. Keep the great work.
This is fantastic! Thanks so much! :D