How to set the parameters for thermal chain in thermal modelling of buck converter demo model?

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1

HI All

I am new to thermal modelling in PLECS and I have followed the demo model Buck converter with thermal modelling to understand the same. How do we decide the parameters for the thermal chain connected to the heat sink and ambient temperature? Is it always a thermal chain or can it be a thermal resistor only?

Thanks

Sneha

2

Hi Sneha!

I am new to thermal modelling but maybe I can help you.

I don’t understand if your problem is how to change the thermal parameters (in this case just double click on the thermal chain) or how to chose them.

It depends a lot on your topology and hardware. Typically, in my models, I create the thermal model through the component datasheet and then add it to the thermal description. (Everything is written in the Plecs manual)

For example, in IGBT component, I added the Foster or Cauer datasheet values so my heat sink block will give me the case temperature. Then I have to model the real heat sink, the thermal grease and the water cooling panel. Every component has its thermal capacitance and a single thermal resistance could be not exact.

3

Hi

Thanks for your response.

yes, I have read the PLECS manual and followed that. I have used SiC Mosfet datasheet and its model for my switch. I have extracted the foster parameters (R1,C1,R2,C2…) from the datasheet.

Now, my question is whether these foster parameters should be inserted to the thermal chain connected with the heat sink or we have to calculate these parameters for heat sink separately and then insert into thermal chain.

If so what will be the process. I am not aware of that.

Is it always a thermal chain or a thermal resistor? How is it decided.

Thanks

Sneha

4

Hi Sneha,

If you have Foster parameters for the SiC device junction-case thermal impedance, I would recommend you include this information in the Thermal Description for the device directly. The RC chain component can represent any material and interface thermally, whether it be the full junction-ambient transitions, or a subset of them, including the junction, case, heatsink, and ambient environment (and other layers/thermal dependencies for that matter). But to answer your question, the thermal chain in the basic buck converter model (in PLECS version 4.2) represents the transitions between the case-heatsink-ambient. But depending on how you want to set up your thermal model, and whether or not you have hierarchical subsystems representing these layers, you can also use just a thermal resistor for a transition.

Is this clear?

Thanks,

Kris

5

Thanks Kris.

I will try these steps and get back to you.

Thanks

Sneha