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Incoherence in loss calculation

0 votes
Even with a simple model of inverter, the results proposed are not coherent in comparison with the theory... I don't understand what happen because I took the Buck model in the Demo and I adapt to my inverter. Could you help me please and explain what's wrong with my simulation?
asked Sep 9 by tanguy (22 points)
You will really need to post a model for anyone to help you with your question.

1 Answer

0 votes
Sorry, can you open it?
answered Sep 10 by tanguy (22 points)
In this model the thermal results seem reasonable and the junction temperatures remain fairly low in steady state and do not diverge.  The issue here is the efficiency calculation will be off since the current delivered from the source during a switching cycle is both positive and negative, leading to a low average power (~20W) but high peak power (~ +/-5000W).

I also am not sure the modulation scheme here is achieving what you would like, but after tweaking the scheme to have 10A DC average current flow the results still seem reasonable.  

Also note in your efficiency calculation you have a scaling factor of 6 to account for the device loading, but there are only 4 devices here, but with a different scheme the devices will be loaded differently and this assumption will no longer be valid.

Regarding your other model, I agree with Kris that your controls do not look correct (for example the grid current is not sinusoidal) and that must be resolved before investigating the thermal performance.
Thanks a lot. Can I unextrapolate the curves to obtain the real curves? Presently switching are perfect whereas I should observe a commutation time?
What curves are you referring to?  Note that the device models in PLECS are behavioral representations of the thermal device characteristics but not reflect the device switching dynamics.