Isolated dc-dc converters - understanding the flow of energy

I have been creating videos on dc-dc converters for close to year. The entire playlist of videos can be found at:

https://www.youtube.com/playlist?list=PL-_jTul4we2TUk7zANWQhGNc6kkJ4hg5J

Typically, when learning power electronics as either an undergraduate or in the early stages of a master's, dc-dc converters are presented one after the other with very little talk about possible links between them or how one could progress from one to the other. During the course of this lecture series, I have been trying to do exactly that - focus on how the converters differ from one another in terms of how the energy flows.

As I have been teaching power electronics, I find that using equations alone to describe the operation of a converter is quite inadequate. Power electronic converters are nonlinear and therefore, equations rarely help to understand how they behave. Equations and analysis can help in designing and optimizing their performance but to understand how they work, it is necessary to understand how energy flows between the different states of the converter and how that fits in with the purpose of the converter.

In the last few weeks, I have been gradually approaching the flyback converter topology. The reason I say I have been gradually approaching this topology is because rather than just present the topology and simulate it, I felt it is necessary to describe how this topology came into being. So, instead of using the opposing winding dot polarity that is characteristic and fundamental in a flyback converter, I use the normal transformer where both winding have a dot polarity at the same (upper) terminal.

The simulation shows what happens when the magnetizing current in the transformer is broken. I show how it is possible to connect a LC filter at the secondary winding to produce a filtered output voltage and additionally how a freewheel diode can be used to ensure the continuity of current through the filter inductor, the main problem arises with the magnetic energy in the transformer having nowhere to go during one stage of the converter operation.

With almost every topology of isolated converters, the main question arises about how to ensure the energy stored in a magnetic component (inductor or transformer) increases and decreases during a switching cycle. If the energy continuously increases which implies the peak current keeps increasing, eventually the inductor or transformer will saturate as the flux corresponding to the peak will be greater than the knee-point of the B-H curve. Additionally, the changes need to happen cyclically and gradually - an increase in current should be following by a decrease.

In general, this is what makes power electronics fascinating - how one can condition power without moving parts but just by ensuring a cyclical flow of power. This is true for any power electronic converter.