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https://reddit.com/r/electricvehicles/comments/moaxh4/go_slower_go_faster_how_exactly/
NormanOfAnstruther
https://www.reddit.com/r/electricvehicles/comments/moaxh4/go_slower_go_faster_how_exactly/


Not sure if this is the right forum, but can anyone explain how the ev speed is controlled? I press the accelerator pedal and it goes faster. I have read “the motor demands more power” but no indication of how this is done.

On a toy, you would use a rheostat to control how much current get to the motor. That is not an option with an ev, so how does it work?

Edit: My thanks to all! I have some reading and learning to do now.

I recommend [https://www.youtube.com/watch?v=yEPe7RDtkgo](https://www.youtube.com/watch?v=yEPe7RDtkgo) — it is an excellent explanation of how to control the frequency and voltage supplied to the motor; and [https://en.wikipedia.org/wiki/Synchronous_motor](https://en.wikipedia.org/wiki/Synchronous_motor) and [https://howtomechatronics.com/how-it-works/how-brushless-motor-and-esc-work/](https://howtomechatronics.com/how-it-works/how-brushless-motor-and-esc-work/) explain how a synchronous motor works.

It is strange to think that in a few years, petrol technology will become a thing of the past, and only old folk will know what 2-stroke vs 4-stroke means, or turbo charging, or synchromesh, or idling … already starting handles, chokes, pinking and retardation are passing into oblivion.



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7 thoughts on “go slower, go faster – how exactly?”
  1. Every EV nowadays (i think) have 3 faze AC (alternating current) motor, you can control them by changing frequency of electricity going into the motor, that change how fast it will spin,

    Or by changing voltage, this will change how much torque motor is generating.

  2. I had a look at this video is probably the best at explaining on how to control speed of electric motors, you have to watch all the way to the end [https://www.youtube.com/watch?v=yEPe7RDtkgo](https://www.youtube.com/watch?v=yEPe7RDtkgo). Note it talks about AC->DC->AC, in a car you only have DC->AC.

    An EV battery is a plain DC battery like any other. To get the right shape of AC power for the engines there is computer controlled power electronics that will set the size and frequency of the power sent to the motor – it is an Electronic Speed Controller as someone else said. When you hit the gas the amplitude and frequency of the electricity will increase, increasing the force (torque) on the rotor.

  3. Even with gasoline engines, the throttle pedal is a torque request pedal. You request more torque by pushing the pedal further down. Lifting the pedal requests less torque.

  4. Think of the accelerator pedal as a lever. The higher up you push the lever, the more power the computer tells the ~~battery~~ motor to output.

    The more you press the accelerator, the more Kilowatts the ~~battery~~ motor is using to propell the car.

    This is more of an ELI5 answer. Obviously it is much more complex, but I couldn’t tell you all the components that it takes to convert the accelerator to the wheels.

    Edit: Technically, the battery doesn’t change outputs, but the controllers determine out much of thier output the motor is using

  5. Pretty much everything runs some form of 3 phase AC motor (induction, permanent magnet, externally excited, etc). An inverter takes DC from the battery and turns it into a matching sinewave for each phase based on where the motor is in it’s rotation and how fast it’s spinning. More rpm means a higher frequency, but you don’t really need to worry about that part while you’re driving, the inverter figures all that out on it’s own.

    In general, the accelerator pedal corresponds to requested torque, which largely translates to how much current the inverter is putting into each phase. With only one gear ratio, it’s going to take a X amount of torque to push the car down the road at a given speed.

    * When requested torque is more than what’s currently required, the car will accelerate.
    * When requested torque matches what’s currently required, the car will maintain speed.
    * When requested torque is less than what’s currently required, the car will slow down in one of two ways: It will either coast until requested torque matches requested torque, or it will apply *negative torque*, aka regenerative braking to slow the car down.

    There’s obviously a bunch of stuff that can be done to filter how the accelerator responds to inputs, and other factors to make it more complex than that, but in general you’re directly controlling torque.

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