Why is MATLAB and Simulink giving me different results when trying to find the closed-loop step response?

for the unity feedback system G(s)= 30(s^2-5s+3)/(s+1)(s+2)(s+4)(s+5) determine the closed-loop step response

>> G = tf(conv([30],[1 -5 3]), conv(conv([1 1],[1 2]),conv([1 4],[1 5])))

G =

         30 s^2 - 150 s + 90
  ---------------------------------
  s^4 + 12 s^3 + 49 s^2 + 78 s + 40

Continuous-time transfer function.

>> H = feedback(G, 1)

H =

         30 s^2 - 150 s + 90
  ----------------------------------
  s^4 + 12 s^3 + 79 s^2 - 72 s + 130

Continuous-time transfer function.

>> step(H)

This is the code I use in MATLAB however, when I generate the model suing Simulink It's giving me a different answer

[ztjona]

I have the same problem, I couldn´t find a solution...

[Rik]

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Response:

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Answer 1

[hashim khan]

I am facing the problem. the step response for one has no overshoot while the same feedback system has a 10% overshoot.

Answer 2

[Kenny]

For this particular closed loop feedback function, the denominator polynomial coefficients don't have all the same 'signs'. At least one coefficient is negative. So this suggests the system is unstable. So if you put in a unit step, the response is going to get out of control already.

Also, rather than type G(s)= 30(s^2-5s+3)/(s+1)(s+2)(s+4)(s+5), it would be better to express it like G(s)= 30(s^2-5s+3)/[(s+1)(s+2)(s+4)(s+5)], just to be clear about the order of the operations.