I so far reduced the blocks to the current sketch. I am not sure what to do with the feedback loop of A and C. How do you move the two summing points A to B. Or is there another easier way to reduce the block in its current form?

 

Think about it: You have three summing points in a row. Isn't addition associative? You can substitute all of these summing points with one.
I also suggest you move the origin of the H1G2 feedback loop from C to the output, making it (H1G2)/(G2G3+G4).
That way you 'll end up with three parallel feedback loops, waiting for you to simplify them.

Is that clear?

 

Here is a link to an application note that discussion block manipulation early on in the text. It reinforces what georacer has stated.

hgmjr

 

Georacer

What does addition associative mean? Does it mean that I can move the summing points around?

 

It means that a+b+c=(a+b)+c=a+(b+c).

In other words you can make a single summing point out of the three smaller ones just by summing all of the components.

 

Georacer

I dont know how to add summing points. But like you said if its a+b+c then I can move the order around like a+c+b, that way I can reduce the feedback loops slowly 1 by 1.

 

A summing point doesn't have to add only two signals. You can lead all three feedback loops to a single summing point.

That said, you will end up with a system whit G1 in series with G2G3+G4 in the forward branch, and three parallel branches for feedback with TFs H1G2, H2/G1 and 1, all of them giving negative feedback.

Isn't that the same as F=G1*(G2G3+G4), G=(H1G2/(G2G3+G4)+H2/G1+1) and the overall TF being H=F/(1+FG)?