in the attempt of implementing a discrete time version of a transfer function I realized that the continuous and discrete versions behave very differently. Here is the tf in the s domain:
0.981 s^2 + 11.32 s + 7.44e+004
Cs = --------------------------------
5.051e+010 s^2 + 5.828e+011 s
using the Octave command:
c2d(Cs,0.002,'tustin')
I get this:
2.088e-011 z^2 - 3.549e-011 z + 2.044e-011
Cz = ----------------------------------------
z^2 - 1.977 z + 0.9772
The response to the same sinusoidal input looks like this:
I cannot explain why this is happening. Can anybody clarify it?
Thank you very much, Guido
Ps: the commands I used are:
Gs_num = [5.0506e+010, 5.8276e+011]
Gs_den = [1.5612e-001, 1.8014e+000, 1.1841e+004]
w_c = 1*2*pi
Cs = tf(w_c, [1 0])*Gs^-1
Cz=c2d(Cs, 0.002, 'tustin')
And then simulink screenshot
