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03-07-2010 04:38 AM

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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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03-07-2010 11:11 AM

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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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03-07-2010 01:13 PM - edited 03-07-2010 01:14 PM

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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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03-07-2010 06:09 PM

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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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03-08-2010 12:35 AM

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And can I transform the Control Vi's to simulation VI's ?

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03-09-2010 03:37 PM

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