MATLAB: Reducing fast dynamic poles in a transfer function.

polestransfer function

Imagine I have a tf that looks something like this: G(s) = 1/((s+70)*(s+5))
Is there some sort of command that can return a transfer fucntion that get's rid of the fastest dynamic pole?
In the example given above my output would be something like this: G(s)=1/(s+5).
Thanks in advance.

Best Answer

Maybe freqsep() is what you want:
>> G=tf(1,conv([1 5],[1 70]))
G =
 
         1
  ----------------
  s^2 + 75 s + 350
 
Continuous-time transfer function.
>> [Gs,Gf]=freqsep(G,10)
Gs =
 
  0.01538
  -------
   s + 5
 
Continuous-time transfer function.
Gf =
 
  -0.01538
  --------
   s + 70
 
Continuous-time transfer function.
>> bode(Gs,h);
The dc gain of Gs will need to be adjusted to match the dc gain of G if you intend to use Gs as a low frequency approximation to G. This doc page is a good source for starters. There are also additional pages in Robust Control Toolbox for model reduction.
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