# LabVIEW

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## Creating model with Control and Design LV2009

Hello,

I'm trying to make a PI control model with Control and Design in labview 2009. I'm tyring to create the following transferfunction:

D(z)=Kp+((Kp*Ki)/(1-z^-1))

But labview adds by itself an extra z^-1 in the Numerator

See the attachment what I have tried. I first want to create 1+(1/(1-z^-1)). What I'm I doing wrong ?

Greetz,

Jeroen

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## Re: Creating model with Control and Design LV2009

Jeroen,

The two expressions "1+(1/(1-z^-1))" and "(2-z^-1)/(1-z^-1)" are equivalent to one another.  They just have the terms rearranged.  Since LabVIEW expresses a transfer function as a numerator and denominator, it is drawing the function as "(2-z^-1)/(1-z^-1)".  You aren't doing anything wrong.

Chris M

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## Re: Creating model with Control and Design LV2009

Ah, stupid off me. Matlab gives the same awnser.

Another question, how do I implant in control and design a Saturation block ? In Simulation there is a standard block but nog for control and design.

I'm trying to determine de P an I values for an embedded PI motor controller.

Message Edited by JvdM on 03-07-2010 01:14 PM
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## Re: Creating model with Control and Design LV2009

Jeroen,

The Control Design VIs create transfer functions, state-space, and zero-pole-gain models, which are all linear, time invariant (LTI).  Since saturation is nonlinear, it cannot be represented by an LTI model.  I suggest using a saturation block in a simulation loop.

Chris M

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## Re: Creating model with Control and Design LV2009

And can I transform the Control Vi's to simulation VI's ?
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## Re: Creating model with Control and Design LV2009

You can use CD Convert Control Design to Simulation VI to convert from Control Design to Simulation

Andy Chang
National Instruments
LabVIEW Control Design and Simulation
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