If I was doing an electric motorcycle, I would use a
DC motor and several small, garden tractor type
batteries. I would select how many batteries are
in the circuit to control voltage and speed.

More sense would be to have a "series/parallel" acceleration control
(just like in DC traction power applications).

I see not much reason to use inversion, AC, phase
conversion etc.

With a motorcycle, battery weight is gonna be a big issue. Anything
you can do to increase efficiency (including AC drive, regeneration,
etc.) is a big win.

There are several companies marketing rather smartly designed electric
bikes using AC propulsion and regeneration. I'm not so sure they'll
ever make money but they are technologically on or ahead of the cruve.

I'm not sure what the market would be for a battery-powered motorcycle,
exactly. Engine-powered bikes are already pretty energy efficient and
way way overpowered for my tastes. Maybe a good-performing (in terms
of endurance, not in terms of getting from 0 to 150MPH in 5 seconds...)
battery-powered unit would find a market. 7.5HP would be just about
the right size.

Tim.