# What is the function of the inductor in the "Dual active bridge" DC/DC converter?

Studying the principle of operation of the DC/DC converter "Dual active bridge", I'm trying to understand what task the inductor (Ls) shown in the diagram performs. The transformer galvanically isolates and regulate the voltage in output side.

I didn't find much information on this inductor. There are thoughts that it accumulates energy, but I'm not entirely sure about this.

Question: what tasks does this inductor perform?

P.S. Maybe someone knows some good articles on this converter?

Thank you!

• What document (provide link) or source did the schematic come from? Jul 11, 2021 at 8:49
• Some inductors like Ls are placed in the "load path" to limit drastically di/dt. When voltage is applied on a transformer ... it can be for "rare reason" "demagnetized" and current can be quickly very high ... Jul 11, 2021 at 13:44
• @Antonio51, Thank you for the answer! Jul 11, 2021 at 14:12

Read this answer that details how a buck converter and a boost converter are combined to produce a synchronous H-bridge buck-boost circuit like this: -

Picture from here. Note that the circuit is bidirectional i.e. power can flow in either direction.

Then, to add galvanic isolation a transformer is used but, to ensure the transformer windings can be driven correctly, you can use a H-bridge driver attached to the primary like this: -

Picture from here. However, this circuit isn't bidirectional so, to permit this, a H-bridge is used on both sides like so: -

Picture from here.

Then, it's a simple matter of where you place the inductor as per this: -

Picture from here.

• Thank you very much for your answer! The Buck/Boost converter example makes the circuit easier to understand. Another question arose. The first figure shows an example with a half bridge. Why is the Full-Bridge topology used here? (Increase power density / correct transformer operation / phase shift) Jul 11, 2021 at 14:09
• I don't understand your question... the first pic shows two half bridges and full bridges at each end are needed for the transformer. Jul 11, 2021 at 14:13
• Now I understand, thank you! Jul 11, 2021 at 15:16
• @Delta if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. Jul 18, 2023 at 13:14

The transformer galvanically isolates ...

Yes

... and regulate the voltage in output side.

No

The transformer merely transforms the voltage in a fixed ratio between primary and secondary. As far as regulation, that is, the control of the voltage is concerned, it does nothing, and could even be deleted (make it a 1:1 transformer, then replace it with a straight through connection).

The inductor handles the difference in voltage between the input and the output side, just like the inductor does in a boost or buck converter. As input and output have a full bridge, this converter will work to boost or buck the input to the output.

Of course the presence of the transformer means that some care must be taken with the control waveforms for the H-bridges, to keep the mean transformer voltage zero.

It may be practical to design the series inductor as the leakage inductance of the transformer, to reduce the number of magnetic components.

• Thank you very much for your answer! Now it has become clearer. Jul 11, 2021 at 13:55

The inductor Ls is needed because the DC side of both full bridges is constant voltage source/load (C1 & C2).

Without Ls, the (constant voltage sources/loads) C1 and C2 (with the help of transformer) would be in parallel connection, which is a bad idea as they might have different voltage.

Constant voltage source connected to constant current load behaves well.

Constant current source connected to constant voltage load also behaves well.

The inductor Ls between C1 (constant voltage source) and C2 (constant voltage load) acts as constant current load (to C1) and constant current source (to C2).