MATLAB Answers

How to find values from a bode plot in matlab

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Uzair Akhtar
Uzair Akhtar on 23 Mar 2020
Commented: Star Strider on 9 Apr 2020
How would I find find these values from a bode plot
wcrit
kcrit

Answers (1)

Robert U
Robert U on 24 Mar 2020
Hi Uzair Akhtar,
According to controller theory you - probably - have to extract the following values:
  • w_crit: probably, the angular frequency at which angle drops below 180° (here your plant response changes sign, thus the controller turns to be unstable. Due to not controllable time delays in the signal chain, usually, there is a phase margin to be maintained)
  • k_crit: absolute gain value at w_crit (as long as your total gain at w_crit is below at least -3 dB the controller will not react to that parts of the signal and a change in sign is not critical. In order to stabilize the controller a gain margin is maintained).
All information needed can be extracted using bode() provided by control toolbox.
Kind regards,
Robert

  2 Comments

Uzair Akhtar
Uzair Akhtar on 9 Apr 2020
Thanks for this, is there a way to extract these values from the bode plot.
Star Strider
Star Strider on 9 Apr 2020
You would likely have to calculate them.
You can get the necessary information from the bode function by requesting outputs from it:
See the documentation for details.

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