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Principle of switch loss of probe module

0 votes

Hello, I am a new user of plecs, and I have questions about probe's calculation of switch loss. 

What is the principle of plecs probe module to calculate the switching loss of the device? According to the official website of plecs, I have learned that the switch loss is determined according to the voltage, current and junction temperature before and after the switch by looking up the table, etc. May I ask which specific moment the voltage and current here refer to (specifically before or after the switch action)?

 Hope to get your reply, thank you

asked Jul 3 by emma2 (16 points)

1 Answer

0 votes
For turn-on loss, PLECS looks at the voltage directly before the switching event and the current directly after.

For turn-off loss, it's the opposite. PLECS looks at the voltage directly after the switching event and the current directly before.
answered Jul 9 by Kris Eberle (1,607 points)
Thank you very much for your answer, but I have some questions about the simulation results. The picture shows the voltage, current and switching loss of SiC MOSFET measured by probe. Why is the waveform of switching loss triangular? I read on the website that it was Dirac Pulse.

Looking forward to your reply

Hello, actually the switching losses are Dirac pulses, but it depends on how you display the waveform type in the Scope. In the screenshot below, I have the same switching loss signal from your model going into all three channels. As you can see in the Data table at the bottom, you can click on the green signal symbols to the right of the signal names and choose options for Auto, Continuous, Discrete, or Impulse. So, in the first plot I set the signal type to Impulse and you see what you expect for the switching losses, but with the second one, the Continuous type, you see the waveforms are connecting the pulse peak from/to zero in the previous/next time step, and so on.

Ok, thank you for your answer, I understand how to set the pulse waveform, but  how to determine the duration of the continuous and discrete options? I have marked the time in the picture below.

 Looking forward to your reply´╝îthank you very much

Hi Emma, to be clear, only the top plot (impulse signal type) is correct and relevant for the switching losses. But as for your question, the duration/width of the other two waveforms is simply based on the step sizes that are taken by the continuous/variable-step solver at any given time. PLECS is not actually integrating these waveforms though- the scope simply "connects the dots" artificially with those signal type options.