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

Question

Manyu Hati 2020-10-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/613566-how-can-i-fix-the-error-that-produces-this-peak-in-bode-plot

编辑： Manyu Hati 2020-10-14

采纳的回答： Ameer Hamza

Bode.jpg

在 MATLAB Online 中打开

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; 
xlim([80 1300]) 

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Ameer Hamza 2020-10-14

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/613566-how-can-i-fix-the-error-that-produces-this-peak-in-bode-plot#answer_513641

在 MATLAB Online 中打开

This is a problem with MATLAB. It is the expected result based on your transfer function. sys_1_vd is a 17-order transfer function. If you look at the poles of the transfer function

>> pole(sys_1_vd)
ans =
   1.0e+04 *
  -1.3334 + 0.0000i
  -1.3334 - 0.0000i
  -1.3333 + 0.0000i
  -1.1605 + 0.0000i
  -0.9684 + 0.0000i
  -0.2047 + 0.0000i
  -0.0869 + 0.0000i
  -0.0026 + 0.0324i
  -0.0026 - 0.0324i
  -0.0029 + 0.0319i
  -0.0029 - 0.0319i
   0.0000 + 0.0314i
   0.0000 - 0.0314i
  -0.0000 + 0.0314i
  -0.0000 - 0.0314i
   0.0000 + 0.0314i
   0.0000 - 0.0314i

You can see several poles are concentrated in region 314 to 324 rad/s. The peak is the effects of these poles.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Manyu Hati 2020-10-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/613566-how-can-i-fix-the-error-that-produces-this-peak-in-bode-plot#answer_513706

编辑：Manyu Hati 2020-10-14

Thank you for your answer. Based on your reply, I finally found and fixed the error. From now on, I will try this advice if I come across a similar issue. Kind regards