OLTC Maggy modelling

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

Hi guys, this OLTC magnifier thing is getting more interesting by the 
minute :D so I decided to put together a model. I basically did a model of 
what I would build:

http://www.scopeboy-dot-com/tesla/mag-nette.jpg

This is a (2,3,4) magnifier based on the same resonator, IGBTs and tank 
capacitor used in my original OLTC. Thus it has the same bang energy and 
output voltage.

I ran a simulation of this and here is the result:

http://www.scopeboy-dot-com/tesla/mg_diode.jpg

Note how the tank cap empties perfectly after 1.5 cycles, gee, just as 
Antonio and Boris predicted it would. Unfortunately, after the IGBT switch 
opens, the tank cap is recharged through the IGBT's anti-parallel diode, by 
the voltage that appears across the primary. The effect is far greater than 
with the 2-coil OLTC. The result is to suck energy back out the system, 
which is bad enough, but worst of all it makes DC resonant charging almost 
impossible.

If the IGBT were a perfect switch that could hold off voltage in both 
directions, the result would be this:

http://www.scopeboy-dot-com/tesla/mg_no_diode.jpg

Which is exactly what we want! Unfortunately, doing this in real life 
requires two IGBTs in series, each with a diode in series. That's four bits 
of silicon in series, thus about three times the cost, and roughly six 
times the losses of a single IGBT carrying the same current.

This would more than offset the efficiency advantage due to the quicker 
energy transfer, and the maggy's slightly lower primary current (750A pk 
vs. 800 for the 2-coil.) And, efficiency advantage was the only reason for 
preferring the maggy in the first place. (Unless its fast rise time has 
magical streamer-growing properties or something.)

My conclusion is that a 2-coil OLTC will give much more bang for the buck 
spent on silicon than a 3-coil one. Unless anyone can persuade me otherwise?

Steve C.