Hi Cal!
Well, it is similar, in principle, to the way an RPC or static converter works, however, it's not the same. ;-}
The reason WHY I did it this way, and WHY it works, all goes back to the physical construction of the transformer. It's a figure-8 core. In it's original 3-phase operation, you had magnetic flux flowing in a figure-8 pattern. Had I set all of 'em up for same polarity, or one in one direction, and the other two reversed, I would have lots of inefficiency- core losses and reactance limiting current, hence, no efficiency.
By putting that center coil between two capacitors, I've set it out-of-phase by 90-degrees, and if you finger-trace the current flows, you'll see that it still makes a figure-8 pattern through the core.
Now, it's not perfect... phase shift is a function of frequency and reactance, and while capacitance is constant, inductance is not (because the secondary is variable)... so the phase shift isn't precise, but it's good enough to work well.
On an AC induction motor, you've got one more set of 'spinning' windings on a 'spinning' core, and it won't be that forgiving, so I wouldn't bet on it working quite as well. Work? Yes, but not as well.
But someone who comes up with a clever idea, could modify this setup and wind up with a variation-on-a-theme that DOES work... it's all about waking up in the middle of the night with a crazy idea.
Dave
This is pretty neat!
You have a three phase output step down transformer with single phase input.
Could this scheme be applied to motor run applications?
Or VFD drive supply, 1ph to 3ph.? A project I am working on at this moment ;-)