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SFRA: Compensation designer bode plot does not match content of .csv file

jorge sola
Intellectual 255 points
Part Number: SFRA

Hello,

I was playing a bit with the Compensation Desginer GUI tool just to experiment with it.

I extracted some PLANT frequency response from a power converter with SFRA, and wanted to use it with the Compensation Designer. Then, i realized that the data showed by the tool does not really match at all with the data stored in the .csv file. Here an example:

There, we can clearly see that the phase crosses the -180 degree at a frequency of around 3 KHz.

However, when I open the file and inspect the values, this is what i see:

I highlighted the points of interest. But, as you can see, in the file, around the frequency of 3 KHz the phase is still around -120 degrees. And the actual jump from -180 to +180 degrees happens at around 5.25 kHz. Therefore,  the shape shown in the compensation designer looks nothing like what the .csv is storing. 

Also, I noticed that when I change the "Control ISR freq", the shape of the plant response also changes, but that should not change it because the file contains pairs of Frequency/Phase or Frequency/Gain. So the actual plotting should be independent of what value I put in the Control ISR Freq. I think that value should only change the parameters for the calculated controller (kp and ki).

Am I missing something here, or doing anything wrong?

Thanks beforehand.

  • 0
    TI__Intellectual 1510 points

    Hi Jorge,

    Sorry for delay in response. Are you providing the same .csv file input to compensator design.exe tool? Because I tried out the same with example.csv and I am not observing difference from plant boded plot from corresponding tool and csv.

    Yes,Shape of plant boded plot should be independent of control ISR frequency.

    It will be helpful if you provide csv file data. So that I can replicate same issue at my end.

    Thanks & Regards,

    Shashank

  • 0 in reply to Shashank Madineni
    Intellectual 255 points

    Hello Shashank,

    Thanks for your reply. 

    Here I attach an example of .csv data that I captured.example.csv

    If you inspect the file, you will see that the phase crosses the -180 degree at around 5Khz, however, when I load this file in the CompensationDesigner (and yes, I am sure that I am loading this exact file),I get the following:

    That picture is with Control ISR set to 25 KHz. If I change it to 50 Khz, then I get the following:

    You can clearly see the difference when selecting different "Control ISR freq".

    If in your case it works as you expect, could it be because I have an old version of the CompensatorDesigner? Are there maybe more recent versions that fix this behavior? Or am i using it incorrectly?

    Thanks.

  • +1 in reply to jorge sola
    Intellectual 255 points

    Hello,

    FYI. I was using the Compensation desginer from DigitalPowerSDK 4.01.

    Now, I have tried to download the DigitalPowerSDK 5.0, and when I execute the Compensation Designer there, it works fine as I would expect. It seems that the old 4.01 version is buggy.