transfer function of sqrt of s

how can i write a simulink model where my transfer function is 1/(sqrt(s)+a) where a is just some constant.

Answer 1

[Mike Borrello]

But wait ... mathematically it is possible! The transfer function is indeed valid! I assume this transfer function was derived from an assumed infinite element network model. The issue is implementation. You need to approximate the square root of s as a series and decide where to cutoff the series as your approximation to the square root. The expression then becomes a high order rational transfer function in s which is linear and which then can be handled by Matlab and Simulink tools.

[Daniel]

How exactly would you approximate it? Can you please provide a sample series approximation?

[Walter Roberson]

See http://mathwiki.ucdavis.edu/Calculus/Series/Taylor_Expansion

and be sure to read the next page in the site for the case where abs(x) > 1, which implies you would need to split into two cases, one for abs(x) <= 1 and the other for abs(x) > 1

Answer 2

[Paul]

This is not possible since it's an invalid transfer function. You should be able to write the tf in terms of s^3, s^2, s etc, which is not possible in this case. Normally you would be able to calculate the tf in Matlab by doing:

s = tf('s')
TF = 1/(sqrt(s)+1)