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How does the Model S motor work?

Discussion in 'Technical' started by ToddRLockwood, Jan 26, 2013.

  1. ToddRLockwood

    ToddRLockwood Active Member

    Sep 11, 2012
    Burlington, Vermont
    I'm curious about the technical aspects of the Model S motor operation. Does the inverter vary both the voltage and the frequency it sends to the motor? If so, how do these relationships relate to pedal position, acceleration, and speed? What part of the design relates back to Nikola Tesla?

    I though there might be one or two people on this blog who can shine some light on this. :wink:
  2. Zythryn

    Zythryn MS 70D, MX 90D

    Mar 18, 2009
    Smoothly and quietly :)
  3. mitch672

    mitch672 Active Member

    Jul 1, 2012
    Stoughton, MA
  4. Red

    Red Member

    Sep 27, 2013
    The motor and drive train basically became available for automotive use only in 1990ies. So it is a recent tech for automotive. Nikola Tesla did make a two phase AC motor a long time ago but could not "steer" it in a fashion required for automotive use. In about 1985 a Yugoslav inventor made the first inverter (frequency converter) for AC motors for industrial use and in 1989 for
    cars also. Up to that point, AC drives were not an option for cars. FIAT, Mercedes, Think, etc..
    jumped on board, as the drive trains were no longer an issue since. Imagine a 500 mile affordable battery today. That is about what kind of a breakthrough that was. Because of that, today only batteries are considered the narrow throat. EV1 was the firs production car using his motors and
    building on those. Some EV1 people then went to AC propulsion and used the knowledge and software for Tesla's drive train. Also for Mini E, etc..

    AC drive trains are excellent in terms of efficiency, durability and in general. While they reach slightly lower peak efficiency than permanent magnet (rare earhts-expensive) motors, the actual efficiency, across actual operating range is typically better.

    They have only one physical contact point in the bearing. Unlike permanent magnet motors, they will not be rendered useless if reaching over 150-160C temperatures, which demagnetize permanent magnets (expensive).

    Tesla, Fisker, MB, FORD, GM with EV1 and Volt,.. etc opted for AC drive trains.

    For full EV's they are simply the best option. Tesla may be doing something wrong with the
    rotor winding, which is likely the culprit for the humming and other noise issues with some
    cars. If done correctly, AC drive trains will last several times the lifetime of a car.

    It is also one of the reasons mainstream car manufacturers were not fans of electric cars.
    Hard to make money with the existing business model, relying on afterservice. Kind of like
    trying to take away revenue from printing cartridges from printer manufacturers, which make
    losses on printers and make money off cartridges. Or gaming consoles, which take a loss on
    the hardware but bring in the $ on games...
  5. Cal1

    Cal1 Member

    Sep 22, 2013
    Battle Ground WA
    So what happens during regen, does it spin the motor backwards? Not being sarcastic but the mechanics of this car is so poorly explained and described.
  6. captain_zap

    captain_zap Electron tamer

    Mar 27, 2012
    Redmond, WA
    No, for an AC induction motor to turn into a generator, the inverter simply needs to drive the motor at a lower frequency than the synchronous speed. This is the speed where the AC field of the three phase sequence is rotating at the same speed as the rotor. When the drive frequency is lowered slightly, current starts to flow backwards through the inverter back into the battery. To turn it back into a motor, the drive frequency is raised to something higher than the synchronous speed, and the current flow reverses and it turns back in to a motor. To reverse the direction of the motor, it just swaps two of the phases. All done electronically. It's a beautiful thing.
  7. hcsharp

    hcsharp Active Member

    Jun 7, 2011
    It varies the frequency, not the voltage. But it's a bit more complicated than that. It actually does vary the average voltage. It turns on the full voltage for very small fractions of a second at a time, then turns it off for small fractions of a second. It varies the amount of time that the voltage is all-on vs all-off to control the average voltage. This is called Pulse Wave Modulation, or PWM for short. When you have the pedal to the floor, the "off" time is at or near 0. In addition, it changes the frequency of the AC cycles.

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