Current is dependent on the motor draw. That is, voltage NEEDS to be around the rated value but current capabilities need to be higher to handle overload conditions.
With that said, all motors can run well above their ratings, up to 2x, for short periods of time without doing damage.
Also, pulse width modulation is definitely worth looking up on wikipedia. All DC conversions use PWM to control the applied voltage to the motor. 120 V on a 115/120 V motor will always use maximum power, which is not desirable in a car. Pulse width modulation turns the signal on and off so it looks like a step function and the average applied voltage is lower.
All conversions use the matrix method because most DC motors run off of 120 V or 144 V motors and use 12 V deep cycle lead acid batteries, generally from the fork lift industry.
I hope this helps. Feel free to ask more
