Understanding Core Loss Measurement

[reson8r]

Hello folks,

I'm looking for a way to measure core loss in RF transformers and inductors. I found a PhD thesis here:
https://vtechworks.lib.vt.edu/bitstream/handle/10919/19296/Mu_M_D_2013.pdf
which looks like just the ticket, but I'm having trouble understanding key parts. I've tried contacting the author with no success.

Chapter 3 introduces a good practical method, but I'm stumped at eqn 3.1 (pg 66).

• Why does P_core depend on capital I_pp and not lower-case i_pp? Capital I_pp results from the magnetizing inductance (L_m in fig 3.1), but lower-case i_pp is the current step due to core loss.
• Why does P_core depend on duty cycle D? Driving fig 3.1 with a rectangular wave would result in a rectangular voltage across R_core, so the power loss in R_core shouldn't depend on D at all.
• Not only do I not understand why D is in there, I don't see how its use in eqn 3.1 is derived.

In short, I pretty much don't get eqn 3.1 at all! If anyone can help, I would greatly appreciate it. Then perhaps eqn 3.2 will start making sense...

Gerrit

 

[reson8r]

I've gotten to the bottom of this, with some help from elsewhere. There is indeed a typo in eqn 3.1 -- I_pp should be i_pp. And page 23 of the paper does touch on core loss dependency on D. Duty cycles away from 50% contain higher harmonic amplitudes, which contribute to higher core loss. That makes sense!