How do you do Unity Feedback on Matlab? (Transfer Functions)

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Joel Okanta
Joel Okanta 2021-1-14
回答： Paul 2021-1-16
Before you get angry, no I cannot post the picture or even do anything of that matter due to the fact that the editor for this Forum got changed, so I can only leave links now. No more image options.
Main Question:
I'm doing a task that involves mapping a Transfer function diagram on MATLAB then completing that block diagram by matlab functions (such as series, parallel, etc.) to reduce the block diagram. However, I am having a problem with doing unity feedbacks on MATLAB, unity feedback looks something like this: https://gyazo.com/18228f771905641513c5b4ebf56a5439 (Note that it's an "empty" line going back)
Where the line has no "H1" feedback signal or whatever, the line is empty and normal going back to a sumamtion point behind the main transfer function block. I initially tried to do F = feedback(F, F) since the signal goes back in itself, but it did not work and instead only worked when I did F = feedback(F, 1). (To confirm how I got the right answer I did a comparison by completing on paper and check online to see if it was correct; matlab was just the odd one out)
Can anyone explain why this is the case?

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回答（1 个）

Paul
Paul 2021-1-16
Check the doc page for feedback()
doc feedback
In this case, the feedback line isn't "empty," it has a gain of 1 (or if you prefer H(s) = 1), which conventionally is not shown explicitly. So in the context of the feedback() command, sys1 = F and sys2 = 1 and you get the correct result.

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