# How to plot bode plot with a transfer functions which are calculated?

조회 수: 10 (최근 30일)
EE_student 2021년 4월 24일
편집: Biral Pradhan 2022년 4월 1일
I am trying to tune a PID controller using Matlab(not Simulink because I am learning/uni coursework).
Problem I need help with
• So, I have a transfer function of a system for which there are phase margin requirement that needs to met
• In order to find the phase advance part of the PID I need to solve a bunch of equations to plot a bode plot using the variables calculated
• https://i.stack.imgur.com/w0LiC.png
I've done this so far
-I tried to replace the tf([num],[den]) with real numbers but that is not feasible as it defeats the purpose of doing this, I want Matlab to calculate the GR and frequency and substitute that into the tf

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### 답변 (1개)

편집: Biral Pradhan 2022년 4월 1일
I understand, you want to calculate the transfer function by substituting intermediate variables calculated with GR and frequency. I went through your live code file, and noticed the use of symbolic variables in tf( ) command. This is not supported. Instead, I recommend creating your ratios symbolic as shown below.
PA = ((Kpa*k*ti)*s + Kpa)/(ti*s + 1);
PI = (taui*s + 1)/(taui*s);
Now, in order to create the bode plots, you need numeric transfer functions. Kindly refer to the below link to obtain the required numeric transfer functions from your symbolic expressions.

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