Power Electronics Lecture

There are 3 EE tutors, and I am one of them. We are each doing a lecture. I'm going to do one on power electronics. I will probably just talk about transformers. I only have 20 min, though.

First, I'd probably talk about what power converters do to give them an overview of what is power electronics.

There's AC/AC, AC/DC (wall-warts), DC/DC (computer supply), DC/AC (not sure when this happens).


Transformers are useful for all types of power converters, but most obviously, AC/AC.

A transformer is two inductors that share magnetic flux.

ok ok ok, let's look at one inductor first. Besides the electrical behavior of an inductor, it also produces a magnetic field so that it looks like a magnet.

If you put two inductors close together like this, they share magnetic field, and the magnetic field created in one induces current in the other.

What is the math behind all this? V = L*di/dt
Faraday's law of induction states that V = N * dPhi/dt where Phi is magnetic flux.

In order to maximize the current induced in the other, we want to maximize the amount of magnetic flux that flows through the second inductor. We do this by wrapping the inductors around certain materials.

All materials have a magnetic permeability. The permeability of air is low and is almost the same as the permeability of a vacuum, which is referred to as the permeability of free space.

Iron has high permeability, so ferrite is often used in transformers.



It depends how they are wound, but in the most general configuration, the turns ratio dictates the relative voltages and currents. Vs = Vp*Ns/Np and Is = Ip*Np/Ns