rlocus showing overshoot, step showing none?

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Robert
Robert 2016 年 12 月 4 日
回答済み: Mischa Kim 2016 年 12 月 6 日
So i have a simple system more or less and rlocus when using the data point is showing overshoot of 13% however stepping the system using the step command clearly shows no overshoot at all. Using the control system designer app also shows no overshoot at all?
Why is the data tool on rlocus showing me overshoot? Ignore the sym2tf command. Its a custom function to go from symbolic to tf data type has worked reliably for years with no issues so i know its not that.
temp = (s+1.4)/(s+5)*(10/(s*(s+1) ))/(1+10/(s*(s+1) )*(9.08*s)/((s+10) ))
rlocus(sym2tf(temp))
%use data tool on the closed loop pole on the rlocus plot and you get 13% overshoot
use step command
step(feedback(sym2tf(temp),1)) % i get zero overshoot
Also from Control design app

回答 (1 件)

Mischa Kim
Mischa Kim 2016 年 12 月 6 日
Robert, the overshoot information that is shown in the root locus plot needs to be taken with a grain of salt. It essentially only indicates how these two poles contribute to the overall behavior of the system.
In other words, in the absence of other poles and zeros these two poles would indeed result in an under-damped system (oscillatory response with overshoot). In your case there are additional poles and zeros that seem to dominate the system behavior.

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