Is my system stable

Hi, My bode and step response is like in the figure in the attachment. poles are on the left but the step response is increasing function. is this stable system ? what should be level, and min max of step response so that we can say about the stability. thanks

Answer 1

[Mayank Dwivedi]

Hi Safiya,

From the Bode plot it is clear that the gain margin of your system is infinite and phase margin is about 100 degrees. Both of them are positive indicating a stable system. However, whether the system is stable or not cannot be directly inferred from the step response plot as your input step value is not clear.

Can you confirm if you are providing a unit step input? Can you please tell what is the step value?. Also the pole seems to be very close to imaginary axes, can you provide the pole zero locations?

-Mayank

[Safiya]

Thankyou for your reply. i used step function step(Hs), Hs is my TF. and the value of the poles and zeros are:

p =

   1.0e+06 *

   0.0000 + 0.0000i
  -3.5030 + 0.0047i
  -3.5030 - 0.0047i

z =

   1.0e+05 *

   -2.4876
   -2.4801

Answer 2

[Safiya]

thankyou for your reply. i used step function step(Hs), Hs is my TF. and the value of the poles and zeros are:

p =

   1.0e+06 *

   0.0000 + 0.0000i
  -3.5030 + 0.0047i
  -3.5030 - 0.0047i

z =

   1.0e+05 *

   -2.4876
   -2.4801