Stabilized performance project

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Hello everyone,

We have a project involving electric vehicles in a leisure center, but we are facing a problem as we need to stabilize the vehicles’ performance (lap times). We are not looking for maximum performance but rather stable performance despite the battery charge level dropping.


Our 21700 battery can sustain 120A continuous up to 15% charge, and the vehicle is set at a max peak of 90A, so there’s no issue there. However, we are losing around 2 seconds per lap between 40% and 100% charge. (Juste because of the voltage decrease)


We absolutely need to find a solution to stabilize the power and compensate between voltage and current to achieve stability.



Is this possible with Fardriver? Or with another controller?





Thank you!
 
Your controller will try to keep the battery current limited to a certain value. As the battery voltage drops, the power will also drop. What you probably want is to keep the power limit constant regardless of battery voltage. One way would be to limit the phase amps to something lower than usual so the battery current limit is not reached. Many controllers can do this, but you need one with programmable phase current.
 
We absolutely need to find a solution to stabilize the power and compensate between voltage and current to achieve stability.
So it sounds like stabilizing is more important than maximizing, so an approach that reduces performance at full charge, that throttles down the initial performance to match the partial charge performance, is acceptable? Many controllers can limit speed or current, so it shouldn’t be too difficult.
 
Fardriver Controller can limit phase current to the motor in the ratios of speed settings.
This setting is the percent of phase current setting for the shown rpm.

You have to lower the values that much, that you will not reach your actuall set battery current with an empty battery and you will loose a little of your overall performance.
Screenshot_20230624_223007.jpg
 
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We have a project involving electric vehicles in a leisure center, but we are facing a problem as we need to stabilize the vehicles’ performance (lap times). We are not looking for maximum performance but rather stable performance despite the battery charge level dropping.


Our 21700 battery can sustain 120A continuous up to 15% charge, and the vehicle is set at a max peak of 90A, so there’s no issue there. However, we are losing around 2 seconds per lap between 40% and 100% charge. (Juste because of the voltage decrease)


We absolutely need to find a solution to stabilize the power and compensate between voltage and current to achieve stability.
It's unclear exactly what end result you want.

If you are just trying to get the same lap time on every lap, then reducing starting performance to match ending performance will do that. Some ways to do this include:
--limit the speed of the system so that it's max speed is the same as it's near-empty speed.
--limit the power of the system so that it's max power is the same as it's near-empty power.

If you are actually trying to get the *end* lap time to be as fast as the *start* lap time that you have now (and doesn't change during the event), then you'll have to make a hardware change to your system, such as:
--increase the battery voltage (number of series cells) to that which gives you an end voltage that is the same as the present start voltage, and then limit the speed of the system so it's max speed is the same as the near-empty speed. (this may require changing your controller and other electronics to handle the higher battery voltage)
--change the controller itself out for one that is FOC that supports FW field weakening, and set that up so that it will give you a faster speed toward end of charge than it does at full charge (may require external hardware (Pic, arduino, Rpi, etc) to vary the FW setting during the event, if the controller does not have this feature built in).
 
The Fardriver Controller can do this, as long as you do not reach the max battery current, the controller can hold the power level constant by increasing the battery current when the voltage drops.
If you also loose topspeed when your battery voltage drops, then you have to limit the rpm of the motor to the max rpm you get when the battery is empty.
 
lifepo4 batteries might be the ticket. Very close to what you want. You'll need a lot of extra room to fit them though.

1737313493012.png
 
Every BLDC motor has an 'absolute' speed limit proportional to the voltage applied (the unloaded running speed) so you can't go above that. If the bikes reach close to that limit, they will slow down gradually with the battery voltage dropping. The controller can't compensate that with more amps.
So, if voltage is the main reason for slowdown, I would look for some way to prevent voltage drop - for example experiment with batteries with same voltage but more capacity (or even lower volts, more amp-hours instead). Then the gradual speed reduction wouldn't be that visible. Or look for some power limit feature in the controller - but if it's about racing then applying such limit can take away the fun from competition. For racing a limit on power is better than speed limit.
 
The Fardriver Controller can do this, as long as you do not reach the max battery current, the controller can hold the power level constant by increasing the battery current when the voltage drops.
If you also loose topspeed when your battery voltage drops, then you have to limit the rpm of the motor to the max rpm you get when the battery is empty.
👍 I think this is what he needs to do. Limit power and limit speed. My thought is that for a leisure center (I’m guessing what they call a family fun tracks around here), they want the performance of all the karts to be exactly the same all the time.
 
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