Thermal loss problem

Question

Hi 

I met an strange phenomenon when using the Plecs to measure the losses. 
I measured submodule’s IGBT(IKW25N120CS7) losses in a MMC system, the switching losses are so high than in the datasheet. As in scope1.

For comparsion, I used a buck circuit to test under almost the same switching conditions, the result is in normal range. As in scope2.

When you compare them, you can find that: for the same switching off behavior, the loss is so high in scope1 with great junction temperature rise. But they use the same IGBT thermal model,  could you please tell me what could be the reason?

Thank you so much for your help!

Comments

You should provide at least your thermal data sheet (xml file) for somebody to give you a hint. Note, however, that the losses usually do not only depend on voltage and current but also on the temperature.

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Thanks a lot for your suggestion. I added the thermal model.

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Are you using a similar Rgon/Rgoff value between the two models? Is it possible for you to share your MMC model?

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I have located the problem. You may not believe it. So I uploaded a video. It is amazing how an unrelated signal to the scope can affect the losses.

 

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Please send your model, including all other thermal datasheets and other relevant information (PLECS version, operating system) to support@plexim.com.