Which is the most accurate way to simulate/calculate the efficiency of power electronics?

Question

I'm trying to simulate the efficiency of an IGBT driven power module. With P_in=P_out+P_loss, the efficiency could be calculated as:

•     eta=Pout/Pin
•     eta=1-Ploss/Pin

As you can see in the model attached, I tried both ways with different models. At first using an ideal switch, then an IGBT with linear loss model (V_f and R_on), then with a thermal description, and finally with both combined. The maximum difference between calculated accuracies is about 1%, which is quite a bit.

So my question is: Which of the described ways is most accurate one?

 

Thanks in advance

Fabian

Answer 1

Hi Fabian,

The second formula is the one to take. One reason for example why they give different results is that the switching losses are not withdrawn from the circuit as PLECS treats switching transitions as ideal. This means P_out calculated from electrical quantities in the circuit is generally different from the term P_in-P_loss, where P_loss is calculated from thermal descriptions.

I hope this helps you.
Best regards,
NF