Ploting root locus, when the gain is in the path and not the loop
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How do I go by ploting the root locus of a system when the K is located in the path and not the loop.
Matlab uses the rlocus function expecting a control system that looks like the one below.
+-----+
---->O----->| SYS |----+---->
-| +-----+ |
| |
| +---+ |
+-------| K |<----+
+---+
I however am looking for the root locus for a system with the gain K is in the open loop transfer function
+---+ +-----+
---->O--->| K |-->| SYS |----+---->
-| +---+ +-----+ |
| |
| |
+-----------------------+
1 Comment
FATIH GUNDOGAN
on 22 May 2021
It had been a while, but might be useful for similar questions.
Keep K=1 (dont use second argument of the rlocus function, it automatically makes K=1)
Just multiply your SYS with a constant gain
and rlocus(SYS)
Answers (1)
Fangjun Jiang
on 17 Nov 2011
Combine your SYS with K into a new system.
Do the root locus for the open-loop system.
If you want to do the root locus for the closed-loop system, K would be 1.
2 Comments
Fangjun Jiang
on 17 Nov 2011
You may be right. It has been a long time since I finished the control theory course or used root locus. All I am trying to say is that you can convert between your two diagrams.
Note that in terms of transfer function between output and input, they are different between your two diagrams.
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