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Old 12-16-2015, 10:50 PM   #2484 (permalink)
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Originally Posted by e*clipse View Post
So it seems that somewhere around 300rpm, the BEMF produced by the motor reduces to some insignificant amount and the controller has to supply power in order to maintain the negative torque command, thus "regen" turns into "reverse" at that point. If the system is purely regen ( power fed back to the supply ) then that would be helpful for extending range. However, if battery power is used to stop the vehicle, then it seems more efficient to use friction brakes at that point.
I think that is what EVTV has done with the brake hydraulic pressure sensor. Pressing on the brake does regen braking proportional to the pressure, before the friction brakes engage. If the regen is not 'enough' to stop you, you put a bit more 'hip into it' and use the friction brakes.

It seems a set-up like this would be nice:
When torque commanded is equal to or greater than the torque required to maintain speed, the controller would consume power from the supply. When the torque commanded is less than the torque required to maintain speed, then then the controller would "regen" power back to the supply. This is essentially what is happenning with a "positive" throttle. It would also "feel" similar to an IC car when downshifting.

If more negative torque is needed, then the driver can hit the brakes. It may be possible to put a sensor on the brakes - either a pressure sensor or a brake pedal position sensor. When the brake pedal is pushed, then the regen could be increased. This reverse torque would only be available when energy flows to the supply. Perhaps the controller could monitor the current flow and basically "ignore" the regen command when it results in power flowing from the supply.

However - and this is where things get tough from a user-interface perspective - the regen torque will be proportional to speed. As this decreases due to the reducing speed, the braking torque from the friction brakes would have to be increased. Most drivers want very predictable brakes, where the negative torque is proportional to brake pedal pressure. Balancing/tuning this will be a challenge, but very rewarding.
At least - that's what I have read. I am not in a position to confirm it ... since my car does not run as yet (and it's DC not AC). Maybe my next project!
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