MATLAB: Step is plotting backwards

controlstepstepinfotransfer function

Im trying yo get the step response the transfunction:
                 244.2 s + 244.2
  -------------------------------------------------
  0.015 s^4 + 1.525 s^3 + 2.51 s^2 + 245.2 s + 1221
but the resulting plot is something kind of reversed:
Why is this happening? is there a way to solve it?
Also stepinfo give me wierd values:
RiseTime: NaN SettlingTime: NaN SettlingMin: NaN SettlingMax: NaN Overshoot: NaN Undershoot: NaN Peak: Inf PeakTime: Inf

Best Answer

The step function is correct.
Your system is unstable.
s = tf('s');
sys = (244.2*s + 244.2) / (0.015*s^4 + 1.525*s^3 + 2.51*s^2 + 245.2*s + 1221);
sys_poles = pole(sys)
sys_poles =
      -101.53 +          0i
       2.2371 +      12.99i
       2.2371 -      12.99i
      -4.6143 +          0i
You have a conjugate pair of poles in the RHP.
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