Root locus analysis MATLAB

Discussion in 'Programmer's Corner' started by TheSpArK505, Nov 29, 2014.

  1. TheSpArK505

    Thread Starter Member

    Sep 25, 2013
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    Hi everyone. Hope U fine.

    I have to sketch the root locus and determine the gain K that satisfies the mentioned specifications .
    The problem is how to treat the controller with the 'K' and what command should i use to do saticfy the specifications??

    look at the attached files
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    The rules of constructing a root locus are quite explicit. You have in the forward path a controller with three possible transfer functions and you have a plant or system with a fixed transfer function. The feedback connection has a transfer function of unity. Among the first rules of constructing a root locus is figuring out how many poles and how many zeros there are, followed quickly by how many branches there are. Where do they begin and where do they end as a function of the parameter K. Can you at least get that far with the three examples?

    Side point:
    What is the open-loop transfer function?
    What is the closed loop transfer function?
    Why are they both important for this analysis?
     
  3. TheSpArK505

    Thread Starter Member

    Sep 25, 2013
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    the problem is that i don't know what commands should i use and what are the procedures?? @Papabravo
     
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    lol
    In my Controls class (third year of four year program) we did it by hand. If you knew how do it by hand, then you would have known the formulas and steps to apply those formulas. The fact that you don't know any of it... is not encouraging.
     
  5. TheSpArK505

    Thread Starter Member

    Sep 25, 2013
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    u r right i don't know how to do it.....can u help me??? @shteii01
     
  6. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    No, it would be too painful to do it over the internetz.

    If you can do this problem on paper, then you can later write the MatLab m-file.
     
  7. TheSpArK505

    Thread Starter Member

    Sep 25, 2013
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    this is the problem i don't know hoe to do it on paper?!!!!

    if u can link me a useful website that talks about it or a pdf!!! @shteii01
     
  8. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Papabravo likes this.
  9. Papabravo

    Expert

    Feb 24, 2006
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    AFAIK there are no canned commands in MATLAB to do a root locus. You have to apply a series of steps that allow you to sketch it. This method was developed in the days before computers were widely available, and it requires a deep understanding of open and closed loop transfer functions. Without that deep understanding any explanation I could offer would go in one ear and out the other. Go back and study the material again and try to answer the basic questions.
    1. How many poles and zeros are we dealing with?
    2. How many branches are there?
    3. Where do the branches of the locus begin and end?
    The answers to these questions require counting and high school algebra -- nothing more.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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