#91🚀 Gapped Foil Inductors Losses - Magnetic Knowledge
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👋 Hello, friends! Dr. Molina here 👨🔧
After my first summer with Marta (my 11-month-old baby), I’m back at the battle!! During September, I will be revealing a lot of news about me and Frenetic.
The summer with a baby is totally different and I have enjoyed playing with Marta on the beach a lot. This edition is relatively long; therefore…let’s start!
Best conference of High-Frequency Magnetics
Next 13th of September we will have Mag&Mad, a scientific conference about magnetics. It’s not a commercial conference; we have put much effort into having the best speakers in magnetics.
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Magnetic Knowledge Library
I’m trying to organize all the articles and knowledge analyzed during the two years of this Newsletter and the work of our CTO Jonas Muehlethaler and our VP of Magnetic Design, Lucas Nicieza, for building Frenetic Online.
This is the index of my Library;
Modeling Magnetics
Core Losses
Winding Losses
Parameters (Inductance, parasitics…)
Design Methods or Considerations
Inductors
Transformers
Flybacks
EMI
New Technologies
Winding
Core
Heat dissipation techniques and materials
Feedback is welcome 🤗.
Gappet Foil Inductors: Losses and Inductance
As you know, we are investing much effort (and money) in the winding losses modeling to be used in Frenetic Online. Our CTO, Jonas Muehlethaler, worked in his thesis on the 2D model for losses in round and litz wires.
His colleagues at ETH continue working on this topic, extending the models to foil windings. Especially Thomas Ewald and Jürgen Biela, [1].
The problem of the winding losses model due to eddy currents and the inductance calculation differs for Litz wire (and round), and foil.
Therefore, Thomas proposed a specific model for gapped foil inductors.
I’m not going to enter the details of the model, but I will comment on the main characteristics of this model.
Inductance model.
The inductance of this gapped inductor is calculated using a reluctance network, applying correction factors due to the gap. However, there is an inductance-frequency dependence, which is important to comment.
The inductance depends of the frequency because of the shielding effect of the foils, which produces inhomogeneous current density distribution in the foil conductors.
This effect is more critical in the foil case than in the litz or round windings.
It’s Analytical
But the beauty of this model is the speed. Thomas proposed an analytical model that means a single equation. This equation is complex but computationally is very fast.
After conversing with some experts, this model could be very interesting if the foil covers the whole window. In other cases, it probably wouldn´t work well.
The model is compared with FEM giving excellent results, as the picture shows.
Nevertheless, the author remarks some differences in the experimental measurements regarding the resistance expected. He said the resistance measured after 300 kHz suffers an effect due to the capacitance or the core losses, where the model is not working as accurately as in the other ranges.
To be honest, I didn´t understand completely the experimental result analysis.
Summary
This model from Thomas Ewald is interesting, fast, and accurate enough to be considered if you are designing an inductor with foil. The model will help you accurately calculate the inductance at each frequency and the losses.
Reference
[1] T. Ewald and J. Biela, "Frequency-Dependent Inductance and Winding Loss Model for Gapped Foil Inductors," in IEEE Transactions on Power Electronics, vol. 37, no. 10, pp. 12370-12379, Oct. 2022, doi: 10.1109/TPEL.2022.3169620.
News from Frenetic
New Lab in Switzerland 🇨🇭
We are establishing relations with the best universities in Switzerland and we already have our legal entity, Frenetic Switzerland and a team of engineers.
New App Note with Cambridge Gan Devices 🚀
CGD has presented at PCIM Asia his 350 W LLC with Frenetic Magnetics
New Lab Director
We have a new Lab director, Francisco Cabaleiro. He obtained his Ph.D at CERN in Power Electronics and has more than 15 years of experience in the field. He will design and manage the extension of our Lab at the Frenetic House.