Non zero steady state error

[garimella]

I have transfer function

T.F = 130s+130/s^3+ 10s^2+130s+130. A step input does not give a zero steady state error . This system is a type2 and some how contradicts the theory. Any body can explain why?

 

[CataM]

First of all is not a type 2, and second of all your transfer function does not even exist, so I think it is a typo.

 

[garimella]

No, it is not a typo, open loop TF= (130/s^2) *(s+1)/(s+10), closed loop TF = 130s+130/s^3+ 10s^2+130s+130

 

[CataM]

No, it is not a typo, open loop TF= (130/s^2) *(s+1)/(s+10), closed loop TF = 130s+130/s^3+ 10s^2+130s+130

If you want someone else to understand what your are writing, use at least standard programming writing of mathematical expressions.

Closed Loop TF (unity feedback) = (130s+130)/(s^3+ 10s^2+130s+130)

Your closed loop TF corresponds to a type 0, nevertheless it has no position error. Kp->infinite and hence position error is zero. You can arrive to the same conclusion using the closed loop TF where the steady state output follows the step input.