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RT Box sampling

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Hi all,

I'm using a Plexim RT Box to control my power converter. In the control file, I'm using PWM blocks. When I configure these blocks, I have same values for the switching frequency "fSw" and the sampling frequency "fSapmling" in my model. However, in the drop-down menu "Update", that I configure as "on carrier minimum", "on carrier maximum", "on carrier minimum/maximum", I have the same result, a sample every "1/fSampling". I was waiting for 2 samples when I have the configuration "on carrier minimum/maximum". Is anybody notice this issue ?
asked Nov 28, 2018 by Didier (15 points)

1 Answer

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Hi Didier,

With PWM Out block, the modulation index (M) is updated with the simulation step, i.e., "fSampling" in your case. However, the digital outputs are refined by the FPGA, enabling the resolution of 7.5 ns. Therefore, PWM edges can occur in between the simulation step.

As given in the "Help" section of the PWM Out block,

with “On carrier minimum” - M will be sampled when the carrier reaches its minimum
with “On carrier maximum” - M will be sampled when the carrier reaches its maximum
with “On carrier minimum/ maximum” - M will be sampled when the carrier reaches its minimum or maximum, whichever comes first -- only once per simulation step 
with “Immediately” - M will be updated after each simulation step of the RT Box

Run the attached model to view and compare the results.

Regards,
Manu

 

answered Nov 29, 2018 by Manu Parimi (144 points)
selected Nov 30, 2018 by Didier
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