Power Loss and Efficiency Calculation of Resonant LLC Converter
Hello,
I am currently trying to rebuild the LLC converter according to the application note "Power Loss and Efficiency Calculation of Resonant LLC Converter". Unfortunately, I do not understand how the values for R_case_ambient are calculated. Is it obtained by varying the value until the temperature at the mosfet or diode is 125°C?
Furthermore I don't understand how to get the values in figure 10. The efficiency is given by efficiency=(Uo*Io)/(Uin*Iin). If I simulate this, however, I come to other values. I have simulated the date of PSIM myself, but I also do not get the exact values from the application note.
Answers
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Hi Philip,
The thermal devices in PSIM contain a thermal equivalent circuit that connects the junction to the case. This thermal equivalent is RC values that describe the traansient thermal network as you move throught the various layers of material. The Gan System datasheets have a nice description, goto, www.gansystems.com to have a look, I screenshot the relevant material.
So this information is used, in the thermal model here:
you can see how R1, R2, C1, etc match.
For R_case_ambient this is the thermal impedance of the path connecting the "case" to the ambient air. This will be the heatsink. You need to look this up from the heatsink datasheets. Below is a typical graph from a heatsink I found on digikey. You need the dC/W number for the airflow you are using.
For the values in the graph of figure 10. It could be that the thermal model has updated or there has been some other change. I will confirm the values.
Albert
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Hi Philip,
I have attached a Word document to answer your questions regarding the application note "Power Loss and Efficiency Calculation of Resonant LLC Converter".
We are examing if there is any error in our calculation but the attached document can answer your questions.
Let me know if you have any suggestions on our method.
Regards,
Amit
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Amit_PSIM_Altair said:
Hi Philip,
I have attached a Word document to answer your questions regarding the application note "Power Loss and Efficiency Calculation of Resonant LLC Converter".
We are examing if there is any error in our calculation but the attached document can answer your questions.
Let me know if you have any suggestions on our method.
Regards,
Amit
Hello,
thank you very much for your/your help. I have applied your tips to my model, however I am still not sure if this fits.I calculated the efficiency for the different load points according to your formula efficiency= P_out/(P_out + P_thermal_loss). However, when I use the formula efficiency = (Uo*Io)/(Uin*Iin) the same values do not come out. What is the reason for this? Shouldn't both formulas be correct?
Attached is a graph showing the calculated efficiency with your formula of my model. For the overview i have also added the whole model
Regards,
Philip
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Hi, Phillip,
You have posted the similar questions in 3 or 4 different places. It is hard to trace which question is answered where.
In theory, the efficiency formula should be:
Efficiency=(Uo*Io)/(Uin*Iin)
However, in PSIM simulation, the waveforms of Uin and Iin include only the conduction losses. They do not include the switching losses. I have explained the reason in another reply to your post.
If other passive components' power consumption can be ignored:
efficiency= P_out/( P_out + sum(P_total_loss from each switching device) )
In PSIM schematic, the signals of Pout and P_total_loss are accessible. You may use computational blocks to calculate this efficiency.
If other passive components' power consumption must not be ignored, the input power should be calculated as:
P_input = Uin*Iin + sum(the switching losses of all the MOSFETs and diodes).
The signal representing the value of the total losses of each device is accessible in the schematic. However, the signal for switching losses is not. Therefore, the efficiency has to be calculated in Simview analysis.
I have sent you an email explaining all those calculations.
Sincerely,
Rhonda
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Altair Employee