1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Unexpected Zeta and Overshoot relation

  1. Mar 15, 2015 #1
    I have a designed feedback control system trying to minimize the overshoot and the setting time. The zeta I (think) ended up with is 0.94. According to this formula:
    I am supposed to have a very small overshoot. However the step response of the system looks like this:
    The poles are:
    0.0000 + 0.0000i (0 is also a zero, so do they cancel?)
    -2.0000 + 0.0000i
    -0.5313 + 0.1740i
    -0.5313 - 0.1740i
    -0.5600 + 0.0000i
    -0.0600 + 0.0000i

    Does that formula apply only for second order system? Or must I have miscalculated something?
  2. jcsd
  3. Mar 15, 2015 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Yes, the pole & zero at the origin cancel.
    Leaving you with a whopping 5th-order system. I wouldn't know any other way than to compute the actual response to a step input, eschewing any and all a priori formulas.
  4. Mar 15, 2015 #3
    Great, thanks.
  5. Mar 16, 2015 #4


    User Avatar

    Your 5th order system has only one dominant complex pole pair with a pole-Q of app. Qp=0.52. The remaining poles are negative-real.
    Hence, I agree with you that we can expect a rather small overshoot only (assuming that the mentioned poles apply to closed-loop conditions).
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted