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How can I convert a transfer function into time dependent using ilaplace

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I have tried to use ilaplace
X2=(F*G3+C*G3)/(1+C*G3); % F,G3,C are transfer functions generated using tf
then i use it to plot a function using plot but when i try to run the code i get an error as shown below
??? The following error occurred converting from sym to double: Error using ==> mupadmex Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.

Answers (1)

Jonathan LeSage
Jonathan LeSage on 17 Oct 2013
The ilaplace function works on symbolic expressions and not transfer function models. You need to convert the transfer function, X2, into a symbolic expression prior to using the ilaplace function.
Here are some links to some relevant functions:
To get you started, here is some example code of one potential method of conversion:
% Your transfer function model
X2 = (F*G3+C*G3)/(1+C*G3);
% Extract the numerator/denominator
[num,den] = tfdata(X2);
% Build symbolic expression using the numerator/denominator
syms s
arrayNum = cell2mat(num);
arrayDen = cell2mat(den);
X2_symbolic = poly2sym(arrayNum,s)/poly2sym(arrayDen,s);
% Valid usage of ilaplace on a symbolic
x = ilaplace(X2_symbolic);

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