Sketching Root Locus of System: K Varies 0 to ∞

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Discussion Overview

The discussion revolves around sketching the root locus of a control system as the gain K varies from 0 to infinity. Participants explore the implications of this variation on the characteristic equation and the resulting poles and zeros of the system.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant requests assistance with sketching the root locus for a system defined by a specific characteristic equation.
  • Another participant suggests plotting the poles and zeros, noting that there are no zeros in this case.
  • A participant expresses difficulty in applying root locus rules due to the nature of K being variable, stating the characteristic equation as (s+2)(s+5)(s+K) + 10K = 0.
  • A later reply presents a derived characteristic equation and expands it, ultimately rewriting it in a form suitable for root locus analysis, identifying the zeros and poles of the system.

Areas of Agreement / Disagreement

Participants appear to agree on the form of the characteristic equation and the method of sketching the root locus, but there is no consensus on the approach to take initially, as some express confusion about the variable nature of K.

Contextual Notes

There are unresolved steps in the derivation of the characteristic equation, and the implications of varying K on the root locus are not fully explored.

Who May Find This Useful

Individuals interested in control systems, root locus techniques, and the analysis of systems with variable parameters may find this discussion relevant.

weavertri
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Hello guys, I need help to sketch the root locus of the system when K is varying from 0 to infinity. (K>=0)
The system:
http://www.freeimagehosting.net/newuploads/anspe.jpg

I'm stuck. I really don't know how proceed.
Thanks in advance.
 
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Plot the poles and zeroes (There are no zeroes here). Use the root locus drawing rules.
 
yeah, that's what I'm doing... the problem is: K is not a constant. to use the root locus drawing rules the characteristic equation of the closed loop system must be written as 1 + GH = 0. All that I got in this case is
(s+2)(s+5)(s+K) + 10K = 0.
 
I guess I finally did it.
my characteristic equation is (s+2)(s+5)(s+K) + 10K = 0.
we expand to s³ + 7s² + 10s + Ks² 7Ks + 20K = 0
the C.E. must be written as 1 + K*F(s) = 0, then

s³ + 7s² + 10s + K(s² + 7s + 20) = 0

1 + K(s² + 7s + 20)/( s³ + 7s² + 10s) = 0



this is equal to

1 + K(s + 3.5 - 2.8i)(s + 3.5 + 2.8i)/(s(s+2)(s+5)) = 0


now we can sketch the root locus where the zeros are (z1= 3.5 + 2.8i and z2 = 3.5 - 2.8i) and the poles p1=0, p2=-2 and p3=-5.

:)
 

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