Quote:
Originally Posted by ldjessee00
I am pretty sure you can come to a complete stop using regenerative braking alone.
This article suggests they are just using normal friction and such forces, but why would an electric motor not be able to reduce rotation down to zero RPM? I have locked an electric motor so it would not turn, then fixed the short and it turned and worked fine afterward.
https://www.caranddriver.com/feature...pedal-driving/ |
Just because you CAN stop a motor with regen braking, doesn't mean that you SHOULD. It's a matter of practical design, more weight, and more complexity. The friction brakes need to be functional anyway.
You can come to a complete stop on an electric motor using electricity only. Below 5 - 7 mph, the motor is not spinning fast enough to generate a high enough voltage to push energy back into the battery pack. I have read discussions about switching to charge a supercap bank below 10 mph, then using that energy to start the car off the line and switch back to the main battery bank. It seems complex for a small amount of energy.
In practice, it appears to take some battery power to stop the AC Induction or brushless DC motor. The details of flux vector control and how it changes near zero rpm are a bit above my head.
DC motors can have the leads shorted and be used as a brake. A resistor is normally required to limit the currents generated this way. Without a resistor, induced currents in DC motors get out of hand quickly.
AC motors in general slow down when the leads are shorted, but the braking is proportional to the current, which is proportional to the speed. Under 5 mph the rolling friction of the tires and the other friction losses in the drivetrain are sort of comparable to the regen braking forces.
It is not easy or convenient to short the leads on an AC motor when it is connected to a motor controller.