Stepping up voltage

[MazdaMatt]

The prius uses a ~200V pack and steps it up to ~500V to drive the motor.

So that got me to wondering... is it reasonable to step up a 12V source to 600V+? This very high voltage could then be used to create a 3-phase drive system using IGBTs and a high voltage industrial motor.

My reasoning:
We all know that higher volts means lower current and the opportunity to get higher speed and performance.
12V batteries could all be used in parallel and batteries could be freely added and removed as budget and damage dictated.
No need to string up 600 volts in batteries, not even 200 for that matter - the safety aspect of not having an exposed high DC voltage is a bonus.

I'm not a power electronics guru, so i'm posing the questions for someone with more knowledge of these things. If 12 to 600 is not reasonable, what is reasonable to step up to 600v? What are the limitations?

[Bicycle Bob]

The only limit I know of is the insulation for higher voltages. To raise voltage, DC is first chopped up and switched to AC, and then run through a transformer. For a 1:50 step-up, you just need 50 turns of thin wire on one side, for every turn of thick wire on the other. For 3-phase, you'd use 3 choppers and 3 transformers.

[MazdaMatt]

See, i thought it sounded simple...

I personally would lean more towards generating a constant high frequency sine wave on the input side, then rectifying the output side and running it through high voltage IGBT's. This way, you get the high efficiency of the step up and you're not trying to run a 1hz wave through the transformer when the motor is just starting to creep.

What about the comparison between a transformer and boost converter? It strikes me that a transformer would be more efficient (no switching losses, etc)... but I'm not sure.