The fun thing about AC inverters is you can draw the basic circuit out on a napkin. Yes, the real thing tends to have a few more parts, but the heart of it's pretty darn simple:
* A converter to make DC - this is generally a rectifier, or GTO/IGBT setup. Pretty simple, really.
* A 'DC link', which is a big filter to get smooth DC at X voltage.
* A 'brake unit' or 'dump unit', this is a resistor and a transistor (on small inverters, it's litterally THAT SIMPLE, on bigger ones, it's pretty close). it presents a load on the DC link, when comanded.
* The inverter - this is little more than 6 IGBTs, or 6 groupings of them, in a so-called 'six pack' arrangement.
Industrial stuff, the brake unit's almost always an option. Just monitors the DC link, if it goes above X volts, it tries to keep it from rising anymore. Of course, any useful DC load can be inserted here, like other inverters (HEP!).
The converter puts out DC at X-Y volts, and shuts off above X-Y. That way the brake unit's not fighting it all day
The inverter just chops it up into AC, under control of the computer, which is anything from an analog circuit (yep) to a 32 bit with DSP and blah blah. The latter type can get <b>amazing</b> control, especially with an encoder. I've seen demos where the inverter plays music with the motor (FWIW, a class D amplifier is basically the same thing).
Somewhere, I had a pdf file with the main traction schematic of a recent Shinkansen series, somewhat simplified. There wasn't much to it..