How performing FRF for complex functions

2023 10 5
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更新时间：2023 10 11
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Hello,
I'm tryiing to plot phase and magnitude plot for below complex transfor function by performing FRF for say -600 to 600 Hz
1257 s + 3.736e05
-------------------------------------------
s^2 + (1554 - 2e02i) s + (3.736e05 - 2e02i)
Please help

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Star Strider
Star Strider 2023-10-5
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Ran in:
Try this —
s = tf('s');
H = (1257*s + 3.736e05) / (s^2 + (1554 - 2e02i)*s + (3.736e05 - 2e02i))
H = 1257 s + 373600 ------------------------------------- s^2 + (1554-200i) s + (3.736e05-200i) Continuous-time transfer function.
opts = bodeoptions;
opts.FreqUnits = 'Hz';
opts.FreqScale = 'linear';
figure
bodeplot(H, {0 600*2*pi}, opts) % Plot Transfer Function
grid
[mag,phase,wout] = bode(H, {0 600*2*pi}); % Return Numeric Values ('wout' Will Be In rad/sec, So Divide It By (2*pi) To Get Hz)
mag = squeeze(mag);
phase = squeeze(phase);
.

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Thank you so much, it helped me, but in the paper I'm refering the magnitude plot is not in DB, how can I change scale? Once again thank you so much.
Star Strider
Star Strider 2023-10-10
Ran in:
Ran in:
My pleasure!
Set the MagUnits option to abs in the bodeplot call —
s = tf('s');
H = (1257*s + 3.736e05) / (s^2 + (1554 - 2e02i)*s + (3.736e05 - 2e02i))
H = 1257 s + 373600 ------------------------------------- s^2 + (1554-200i) s + (3.736e05-200i) Continuous-time transfer function.
opts = bodeoptions;
opts.FreqUnits = 'Hz';
opts.FreqScale = 'linear';
opts.MagUnits = 'abs';
figure
bodeplot(H, {0 600*2*pi}, opts) % Plot Transfer Function
grid
[mag,phase,wout] = bode(H, {0 600*2*pi}); % Return Numeric Values ('wout' Will Be In rad/sec, So Divide It By (2*pi) To Get Hz)
mag = squeeze(mag);
phase = squeeze(phase);
The units returned by the bode function are absolute for ‘mag’ and degrees for ‘phase’. Use the mag2db and deg2rad functions to convert them to dB and radians to change them if you need to. The ‘wout’ units are radians/time unit, so divide them by (2*pi) to get Hz.
.
Star Strider
Star Strider 2023-10-10
If my Answer helped you solve your problem, please Accept it!
.
Once again thank you so much, Now I'm trying plot the root locus using rlocus(), and it says
Error using DynamicSystem/rlocus (line 65)
Cannot compute the root locus of models with complex data.
May be I need to rewrite my transfer function, I will get back to you if I have any questions.
Star Strider
Star Strider 2023-10-11
My pleasure!
I cannot suggest a work-around for the rlocus problem.

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