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[SOLVED] lc filter transfer function

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danilorj

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Hey guys,

I'm sending you a picture of a equivalent model of the output LC filter in the laplace domain. Could you, please, tell me how I can implement this in simulink. Because the transfer function LC*s^2+1 cannot be implemented in simulink, it shows a warning that the degree of denominator must be equal or greater than the numerator.

https://obrazki.elektroda.pl/5960581300_1406287989.jpg
 

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The warning sounds reasonable. How did you derive the transfer function?
 

i was thinking of writing this equation in a different way so it could be implemented in simulink, but i don't think it can be done. Does someone have any idea?
 

Well, that is not a valid transfer function. It's only the frequency domain representation of the output.
Transfer function is the ratio of output/input and not simply the output expressed in frequency domain.
Re-check your link carefully.
 

So I think the author of this article made some mistake. The way it is depicted in figures 9 and 10 of this link I sent, the author uses this expression LC+s^2+1 and it cannot be implemented.
 

The voltage input to this transfer function is of a particular fixed form. The voltage contains the same term in the denominator, thus effectively canceling it. See the expression for Vg(s)
The block being discussed seems to simply normalize the voltage.
 

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O don't think the voltage contains the same term in the denominator. The expression for vg= Vm*sin(w0*t).
 

How can Vg(s) be in terms of t!?
See the expression for Vg(s) in the attachment. The sinusoidal nature of Vg(t) anyway suggests an s^2 in the denominator of Vg(s)
 

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The expression for the input current ig(s) contains a differential term Cf s vg(s), which describes the filter capacitor current. It should be possible to model it in Simulink.
 
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