Probably the biggest advantage of AC motors is that they can
be used for braking as well, much like an engine or ‘jake’
brake on a big rig which slows the engine speed, thereby
slowing the vehicle.
The real cool part is that the energy used in braking can be
converted into power to charge your batteries giving you a
longer charge.
It is called regenerative braking and is used on all of the
newer electric cars developed by the car companies. The
regenerative capacity is built into the controller, and that is
why it is sold as a package, and also why the price is fairly
steep.
Even more important is that AC motors can produce much
higher power ranges for the same sized motor when
compared to DC. If weight is a critical factor in your design
you might want to use an AC motor.
Most AC motors are connected to the drive axle, but you can
connect them to the transmission too.