BH curves of a planar tranformer forward converter

Hi,

Here are two articles that I found on Internet :
The first one


I explain what you can't see from the extract here. The method explained above is the following for finding the Flux swing of the transformer
1 : Give the allowed temperature rise (°C rise)
2: Compute the dissipated power into the transformer (Pcore + Pwinding) by using the thermal resistance that you will find into the datasheet of your selected core.
3: Then by knowing the effective volume of your core, compute the dissipated core power Pcore per cm3
4 : Knowing the dissipated core power Pcore per cm3, see what is the corresponding Flux density peak associated to this dissipated power. Example :


5 : Double it to find the flux swing ... I do not understand this line

In a forward topology, the transformer operates only in the first quadrant BH-curves. I mean in this zone:


So there is no reason to double the flux swing. I could understand to double the flux swing if it was a flyback or a push pull topology... Is there is someone which can help me why this assertion is true ? I find it again on the follwing article :



Thank you very much and have a nice day !

Léo