Discrete transfer function show different results in Simulink and in Matlab!

I have a discrete transfer function,

s = tf('s')

Gs=(5*s+1)/(s^2+2*s+1)

The step response of Gs is;

then descritize Gs with Zoh with T=0.001,

Gz_inv =

z^2 - 1.998 z + 0.998

---------------------

0.004996 z - 0.004995

Step response of Gz is;

Both results are the same, that is good.

Let s do the same thing in Simulink;

As you see below, the the step responses of Gs and Gz DO NOT match each other! Gs's response is the same as the one in Matlab, but the Gz's response is like a ramp output!

Where is the problem? Why the discrete Gz's response does not match to either Matlab's result or Gs's step response? Can you please help on that?

Thank you

Murat Gozu

Answer 1

[Navya Seelam]

Hi,

This might be because of the unstable poles in discrete transfer function. Try using LTI block instead of discrete transfer function block.