Re: plotting transfer function in octave 5.2: How to fix error: set: "dataaspectratio' must be finite

Hello Torsten,

I was going analyze everything the continuous domain and then convert to the
discrete domain.

Analysis would consist of doing the following:
1. first, find P and I gains for G1(s) that gives a good step response and
also makes the inner current loop stable.
2. Reduce the inner and outer loop to one block.
3. Next, find P and I gains for G2(s) that gives a good step response and
also makes system stable.
4. Convert everything to discrete time domain and compare continuous to
discrete response.  Before converting the continuous time to the discrete
time I would remove the continuous zero order hold from the system and then
use the ZOH method to convert the final equation to discrete domain.  Is
that the correct way to do it?  Or should I just convert G1(s) and G2(s)
using the ZOH method and convert the others using the tustin method?

The whole process might take several iterations.
I have been using https://www.youtube.com/watch?v=yetLPW9sQaI,
https://www.youtube.com/watch?v=rNMlaq8xABE and several other youtube video
and websites to gain an understanding of how to analyze the system.

The actual diagram is a little bit more complicated than what is shown in
diagram I posted.  There are actually two feedbacks in the inner current
loop: an inductor current feedback (positive feedback) and an output current
feedback (negative feedback).  Adding these two together you will get
capacitor current (Icap = Iinductor - Ioutput).  Also, the voltage reference
is fed forward and summed right after ZOH2(s) or G2(s) depending on which
diagram is being used.

Stephen


 



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