Fitting Impedance data file to parallel RLC circuit model using fmincon

20 views (last 30 days)
Hello
I am trying to fit an impedance data file from simuation to a parallel equivalent RLC circuit model. attached is files needed to run the fmincon optimaztion command.
Please any help will be appreciated.
  5 Comments
Star Strider
Star Strider on 3 Dec 2021
The parameter estimation or optimisation will not work with incomplete data.
I will leave you to explore this at your leisure.
Good luck, and have fun!

Sign in to comment.

Accepted Answer

Mathieu NOE
Mathieu NOE on 3 Dec 2021
hello
my attempt below - with just fminsearch (as I don't have the Optimisation Toolbox)
I refined a bit the IC by manual serach , not even sure it was needed. ...
clear all
clc
load('Y_adm.mat')
figure(1)
freq = freq*1e9; % must be GHz
Zp = 1./Yp1(:); % measured
R0 = 100;
L0 = 35e-012;
C0 = 1/(L0*(2*pi*5.85e9)^2);
x = [R0 C0 L0]; %from ADS
Zth = 1./((1./x(1)) + (1i.*2.*pi.*freq.*x(2)) - (1i./(2.*pi.*freq.*x(3))));
semilogy(freq,abs(Zp),'b',freq,abs(Zth),'r')
grid on
% curve fit using fminsearch
x = freq;
y = abs(Zp);
f = @(a,b,c,x) abs(1./((1./a) + (1i.*2.*pi.*freq.*b) - (1i./(2.*pi.*freq.*c))));
obj_fun = @(params) norm(f(params(1), params(2), params(3),x)-y);
sol = fminsearch(obj_fun, [R0,C0,L0]);
a_sol = sol(1);
b_sol = sol(2);
c_sol = sol(3);
y_fit = f(a_sol, b_sol,c_sol, x);
Rsquared = my_Rsquared_coeff(y,y_fit); % correlation coefficient
figure(2)
plot(x, y_fit, '-',x,y, 'r .', 'MarkerSize', 20)
legend('fit','data');
title(['Gaussian Fit / R² = ' num2str(Rsquared) ], 'FontSize', 15)
ylabel('Z', 'FontSize', 14)
xlabel('freq (GHz)', 'FontSize', 14)
R = a_sol
C = b_sol
L = c_sol
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function Rsquared = my_Rsquared_coeff(data,data_fit)
% R2 correlation coefficient computation
% The total sum of squares
sum_of_squares = sum((data-mean(data)).^2);
% The sum of squares of residuals, also called the residual sum of squares:
sum_of_squares_of_residuals = sum((data-data_fit).^2);
% definition of the coefficient of correlation is
Rsquared = 1 - sum_of_squares_of_residuals/sum_of_squares;
end
  8 Comments
Mathieu NOE
Mathieu NOE on 13 Dec 2021
hello again
ok, I can see the result
but I am a bit lost by the fact that you have some many degrees of freedom (AB_amplitudes, AB_phase, dx, dy,...) and your only target is to get a directivity plot centered at 30°
seems like an overdetermined system to me...

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!