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In a forward converter, the current through the physical primary winding is the sum of the current through the magnetizing inductor and the current through the model primary winding.

However, the current through the physical secondary winding is equal to the current through the model secondary winding, and the current through the physical tertiary winding is equal to the current through the model tertiary winding.

Why is the physical primary winding different from the model primary winding, when the secondary and tertiary are the same?

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1 Answer 1

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Consider the diagram,

schematic of forward converter

(Power Electronics, Hart, D. W. (2011), McGraw-Hill)

The magnetizing inductance Lm can simply be placed anywhere, making suitable adjustments with respect to turns ratio and leakage inductance of course. It only needs to be accounted for once.

If we aren't accounting for leakage, k12 = k23 = 1, then no leakage adjustment is necessary and placing it on any winding (adjusted for turns ratio) shows the same current flows in branches outside of the transformer.

For nonideal transformers, the windings can be modeled as some self-inductance per winding, coupled through series (leakage) inductors, to an ideal transformer handling the turns ratio. Usually, k is high enough in practical cases that just one magnetizing inductor suffices, and series inductor(s) for leakage.

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