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OK, Good guesses everyone.
Tesla is using an Inverter Drive on a 3 Phase AC motor. These Inverter Drives or Variable Frequency Drives (VFD's) are the nearest thing to freaking magic as you'll find anywhere.
The 3 phase induction motors are really fascinating things too. They are designed for a specific frequency and voltage in order for the windings to draw the correct safe amount of current. they are designed to run at 60 hz either for 3,600 RPM (~3,530 really) 1,800 RPM (1750) or 900 (870).
Basic 3 phase motor theory has the Stator windings generating a rotating magnetic field around the rotor. The rotor generates a magnetic field due to the induced current of the stators rotating field. The rotor than tries to keep up with the stator field, thus generating torque. Under low or no load, the "Slip Rate" of the motor is low....therefore the field is weaker...therefore not as much torque can be produced. If you load the rotor, you increase the slip rate, using more electricity to generate a stronger field and more torque. You can load the motor up to the point where you max out the rotors ability to generate a field and then it stalls.
The design of the field windings (stator) and the rotor itself have a huge impact on how the motor behaves. This divides motors into basic groups known as Design B, and Design D primarily. The B Motors are for constant loads and designed to generate much higher torque for a small increase in slippage, (a fan) but they stall quicker (at lower relative slip rates) generating their max torque at high RPM and do not generate much stall torque. Design D motors slip more generating greater torque gradually as they slip more and have a very high starting torque. (Oil derrick pump) The thermal design characteristics of a motor have a huge impact on how it is rated as well.
CEMF applies to DC motors but not so much with the 3 phase motors. CEMF refers to how a DC motor will eventually limit its speed due to the motor acting as a generator in order to limit the current and therefore the speed. Since a 3PH motor cannot run without a certain amount of slip rate, it is impossible for it to overspeed beyond its design RPM and correlated frequency.
The beauty of an Inverter is that it is able to trick a nominal 3,600 RPM motor into thinking that it is running at its rated 60Hz even though it is spinning at 0 rpm or 7,000 RPM. The inverter does this by sending a variable voltage and frequency sinewave to the 3 individual windings in order to generate the desired current and frequency in the rotor that locks onto the stators rotating field and generates the desired amount of torque.
Torque, at the end of the day, is really the thing we are looking to create. The answer to current OP's current draw question is thus a bit complicated, but I believe that the current draw matches power at frequencies below 60hz, FOR A GIVEN TORQUE. (Constant Torque) Then current draw is constant at frequencies above 60hz, FOR A GIVEN AMOUNT OF HORSEPOWER PRODUCED, while the torque delivered starts to decrease as the RPM goes above the rated RPM at 60HZ. (Constant Horsepower)
That all said....THE REAL ANSWER IS --->> The biggest factor in current draw is Load. Not RPM. For a given RPM using an Inverter, the current draw can be minimal or up to the max in order to generate the maximum rated torque.
I sold 3 phase motors for Lincoln Electric back in the 90's and have a pretty firm grasp on 3 phase motor theory, if I didn't explain something here clear enough than lets talk about how to make it clearer. Tell me I am somehow mistaken on how these motors work, you do so at risk of looking mistaken yourself later on. Google "3 phase motor theory" and "Variable frequency drive" for a lot of detail.
Hope this helps!
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