just to muddy the waters a bit, most of the ac controllers I've seen actually have a coil, for "power factor correction", but the result is that it can bump the 300 volt battery up to 500 volts (with a corresponding drop in current and some losses).
I haven't studied many DC controllers but I haven't seen such a device employed there solely as a boost converter. Though there is certainly appeal in being able to make higher voltage from fewer large and cheaper batteries, I don't know what the tradeoffs are exactly. Bet someone here does though
