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## Re: How can I fix the error that produces this peak in Bode plot?

 From: Doug Stewart Subject: Re: How can I fix the error that produces this peak in Bode plot? Date: Wed, 14 Oct 2020 07:23:19 -0400

On Wed, Oct 14, 2020 at 7:02 AM Beginner1 via Help-octave <help-octave@gnu.org> wrote:
Hi,
I am plotting a Bode diagram of a simple resonant control function for a RL
load and there is a 'sharp peak' around the target frequency on both the
magnitude and the phase diagrams. This sharp peak should not appear and
without it, the bode plot would be correct. Could you please give me an
intuition on where the problem is? I know that it has nothing to do with
the kp_1 and ki_1 parameters, since this peak appears for the complete range
of them. I think there is something wrong on how Matlab treats some
integrators but I am not sure. Here is my code:

Ub=400/sqrt(3);
Ib=3.3;%
w_b=2*pi*50;
Zbase=(Ub)^2/(sqrt(3)*Ub*Ib);
Lbase=Zbase/w_b;
Td=0.00015;
Rf=0.1;
Lf=0.0018;
R=Rf/Zbase;
L=Lf/Lbase;
w=2*pi*50;
kp_1=2*pi*1000*Lf;
ki_1=(Rf/Lf)*kp_1;
s=tf('s');
G_pwm=(1-(Td/2)*s)/(1+(Td/2)*s);
G_i_1=kp_1+ki_1*s/(s^2+w^2);
sys_1_vd=(G_i_1*G_pwm)^2/((L*s+R+G_i_1*G_pwm)*(G_i_1*G_pwm+L*s+R-(1-G_i_1)*G_pwm));
bode(sys_1_vd,'r');
grid on;
<https://octave.1599824.n4.nabble.com/file/t372684/Bode2.jpg>

--
Sent from: https://octave.1599824.n4.nabble.com/Octave-General-f1599825.html

First ---->  this is not a matlab group.

second :
did you know that you have a zero at +13333.33?
use the rlocus(sys) command to see.

--
DAS