CODEWITHSUNDEEP
matlabplot
Electrical_engineer_student
Electrical_engineer_student

Reputation: 59

Problem with defining a transfer function for Bode plot in MATLAB

I am trying to tune a PID controller using Matlab(not Simulink because I am learning/uni coursework). 1. Summarize the problem:

2.Describe what I've tried

Problem

Error Full_Code: https://drive.google.com/file/d/1sWUnvvye_RBXGL8-nWq___3F5UDmDOoG/view?usp=sharing

Minimum reproducible code example:

clearvars;clc;clearAllMemoizedCaches;clear

syms s w 

%--------------TF of the aircraft

G(s)= (160*(s+2.5)*(s+0.7))/((s^2+5*s+40)*(s^2+0.03*s+0.06));

k= 8;  % selected k value range 4<k<8

Max_PA=asind((k-1)/(k+1)); % computes max phase advance

Centre_dB= 20*log10(sqrt(k)); % computing centre gain in dB

Poi= -120-Max_PA  % looking for Point of interest(Poi)

tf_int= subs(G(s),1j*w); %intermediate transfer function

eqn= atan2d(imag(tf_int),real(tf_int))==Poi; % solve for w at Poi


% computing crossover freq(wc)

wc= vpasolve(eqn,w); % find exactly the wc at Poi

GR=20*log10(abs(subs(tf_int,w,wc))); % find the gain at at wc

Kpa= 10^((GR-Centre_dB)/20);

ti= 1/(sqrt(k)*wc); % computing Kpa and ti

num1= [Kpa*k*ti,Kpa];

den2= [ti,1];

PA= tf(num1,den2) %PA tf defined

Upvotes: 1

Views: 269

Answers (1)

Ander Biguri
Ander Biguri

Reputation: 35525

Yo are trying to input non-numerical (symbolic numers) values into tf, which only accepts numerical arrays. You can convert them to that with double()

PA= tf(double(num1),double(den2)) %PA tf defined

Upvotes: 1

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