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Finding overall gain and phase of a system

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yashvin
yashvin 2014-3-19
回答： yashvin 2014-3-19
In a simple way,here is what I intended to do :
I have got 2 transfer functions G1 and G2. Gn is not a transfer function but has got a gain and a phase.
s=tf('s')
G1=1/s;
G2=5/s^3;
I want to find the overall gain and phase of the system at the frequency w=1. I can get the gain and phase of G1 and G2 at w=1 by:
[m1,p1]=bode(G1,1)
[m2,p2]=bode(G2,1)
m1=1,p1=-90
m2=5,p2=-270
Assuming my gain at w=1 for Gn is 5 and the phase is -100 degree. How can i find the overall gain and phase of the system at w=1. The closed loop positive feedback is
Cloop=G1/(1-G1*G2*GN)
Thanks
Yash

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回答（2 个）

Arkadiy Turevskiy
Arkadiy Turevskiy 2014-3-19
编辑：Arkadiy Turevskiy 2014-3-19
freq=1;
resp=5*exp(i*2*pi/360*100);
Gn=frd(resp,freq);
[m3,p3]=bode(Gn)
m3 =
5.0000
p3 =
100
Cloop=G1/(1-G1*G2*Gn);
[m4,p4]=bode(Cloop,1)
m4 =
0.0397
p4 =
-12.2403
yashvin
yashvin 2014-3-19
Hi Arkadiy,
Thanks for your reply.
But if my phase of Gn is more than 180 or less than -180 degree,
For example taking a phase for Gn to be 200 degree,
freq=1; resp=5*exp(i*2*pi/360*200); Gn=frd(resp,freq); [m3,p3]=bode(Gn)
m=5 but p3=-160.
How can i represent the resp for any magnitude of phase . Phase can Gn can take values of 500 degree or -400.
Is there a necessary way of representing it without losing my phase?
Thanks
Yash

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