AC motor must be run off inverted DC?
A frequency converter for motors also known as a variable frequency drive (VFD) is capable of a softer start than any other means of motor starting. A motor that is intended only for VFD use could draw significantly higher starting current if started by the methods usually used for motors connected to a 3-phase power source.

The easiest way to design a motor for high power density is to design it for a frequency higher than 50 or 60 Hz. For a vehicle, the voltage would likely be no more than the usual 3-phase industrial supply voltage range, 200 to 600 volts. If a motor is designed for 400 volts and 200 hz, it could operate at other frequencies if the V/Hz ratio, 2 V/Hz is used. For 50 or 60 Hz, that would mean that anything higher than 100 or 120 Hz would be excess voltage. Connecting to a normal 3-phase supply would likely mean connecting to excess voltage.

Either of the above two situations represent trouble if the motor is connected directly to a 3-phase supply.