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Re: plotting transfer function in octave 5.2: How to fix error: set: "da

From: Doug Stewart
Subject: Re: plotting transfer function in octave 5.2: How to fix error: set: "dataaspectratio' must be finite
Date: Mon, 3 Aug 2020 11:09:53 -0400

On Mon, Aug 3, 2020 at 2:42 AM shall689 <> wrote:
Thanks Doug and Torsten.

I have been working on several things and I am not even sure how I got a 8th
order polynomial equation.  Currently, I am only getting a 3rd order
polynomial transfer function and I am able to plot its step response. 

Do either of you know of a good Digital Controls book?  I have a Inverter
Control diagram with both an inner current and outer voltage control loop
and I am stuck on whether or not to add zero order (ZOH) hold to both.
Currently I am only adding the ZOH transfer function right after the inner
current loop PI. 

My understanding is:
 When you convert analogue to digital you need a hold function because the ideal sampiler just knows the values at the sample point(time) but has no knowledge of the voltage between the samples. But a real a/d converter keeps the sampled voltage there until the next sample. thus we get the stair step pattern. Now there are many "hold functions" and which one to use depends on what your needs are. If you want accurate results for a step input then use the ZOH. If you want frequencies to be close then a tustun would be better. If you want impulse response then a different method must be used etc.

DASCertificate for 206392

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