Bode Diagram

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Amir
Amir 2011-4-27
评论： Walter Roberson 2024-10-15
When I plot a bode diagram from a FRD sys (obtained by a measurement data), I encounter phases beyond [-180,180]; actually, their order is about 2000 degrees! What should I do in order to have them inside [-180,180] degree?

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Arkadiy Turevskiy
Arkadiy Turevskiy 2011-4-27
You need to use bodeoptions command and set PhaseWrapping to on. Here is an example showing how to do it:
>>s=tf('s'); %define Laplace variable
>>freq=logspace(-1,2,1000); %define frequency vector
>>sys=1/(s^3+2*s^2+3*s+1); %some tf with phase <-180
>>bode(sys,freq) %phase is not within -180:180
>>p=bodeoptions
>>p.PhaseWrapping='on'
>>bode(sys,freq,p) %phase is wrapped inside -180:180
HTH, Arkadiy
  1 个评论
Amir
Amir 2011-4-28
Thank you very much. It worked for me :)

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更多回答（2 个）

Benjamin Hoepfner
Benjamin Hoepfner 2022-6-29
Hi,
i'm using version 2021a and i have a similar problem but the previous answer doesn't work in my case. I need the values of the bode(sys) function for further calculations or external data storage. But the phase wrap obviously doesn't work in this case.
Here is my Code:
%same system from the previous answer
s=tf('s');
freq=logspace(-1,2,1000);
sys=1/(s^3+2*s^2+3*s+1);
[M1,P1,w1] = bode(sys,freq); %saving the magnitude,phase and frequency from the system via bode(sys)
X1=[]; %saving the datas in an extra variable
X1(:,1)=w1;
X1(:,2)=M1;
X1(:,3)=P1;
p=bodeoptions;
p.PhaseWrapping='on';
[M2,P2,w2] = bode(sys,freq,p); %same step as before but with the phase wrap option from bodeoptions
X2=[];
X2(:,1)=w2;
X2(:,2)=M2;
X2(:,3)=P2;
figure(1)
semilogx(X1(:,1),X1(:,3),X2(:,1),X2(:,3)) %plotting phases from X1 and X2 over frequency
legend %two curves with same datas..
Is there anybody out there how can help me with this or can give me an explanation for this?
Best regards!
Ben
SRIMATHI
SRIMATHI 2024-10-15
编辑：Walter Roberson 2024-10-15
same system from the previous answer
s=tf('s');
freq=logspace(-1,2,1000);
sys=1/(s^3+2*s^2+3*s+1);
[M1,P1,w1] = bode(sys,freq);
X1=[];
X1(:,1)=w1;
X1(:,2)=M1;
X1(:,3)=P1;
if true
% code
end
p=bodeoptions;
p.PhaseWrapping='on';
[M2,P2,w2] = bode(sys,freq,p);
X2=[];
X2(:,1)=W2;
X2(:,2)=M2;
X2(:,3)=P2;
figure(1)
semilogx(X1(:,1),X1(:,3),X2(:,1),X2(:,3)) ;
  1 个评论
Walter Roberson
Walter Roberson 2024-10-15
W2 is undefined.
MATLAB is case-sensitive. w2 is not the same as W2

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