[MPaulHolmes]

Yes, that's what I was trying to say (the picture). The throttle ideally is a wig wag. In the DC case, throttle is proportional to current. In the AC case throttle is proportional to Iq, which is still basically the motor's torque. But in the AC case with field oriented control, you do regen just by commanding a negative Iq. The PI loop makes the current follow throttle position. Even though the battery voltage is maybe only half, the current won't be large because the the Iq current would have very quickly converged to the throttle position due to the PI loop.

Not batteries connected to the output of the boost converter. Rather, the boost converter sort of bypassed backwards, so the current just goes right through U, thru the inductor, and to the batteries.

Edit: negative Iq just means negative torque, so slowing down. Care would have to be taken to ensure that the negative Iq didn't result in too big of a current to the batteries. But with a simple current feedback for the battery pack, you would be able to just limit commanded negative torque. Like when you limit limit battery amps in the dc case.

Actually, you wouldn't need a battery current sensor I don't think. In the DC case, to limit battery amps, you use the relationship
ampsBatt = PWM_DUTY * ampsMotor. So, when you monitor ampsMotor, and you know PWM_DUTY, you can just know ampsBatt. I think it would be analogous in the AC case. Instead of ampsMotor, it would be Iq (the current that is rotating, but "fixed" in magnitude, and is responsible for the torque).

I was just noticing that the 3 high side controllers that the beta testers are using right now could be used as boost converters just by adding an inductor to the 3 M+ cables. Then, the other side of the inductor would connect to the low voltage battery bank B+. Then, the normal B+ and B- on the DC controller would connect to B+ and B- of the AC controller. Then, if you had a 1000amp inductor (haha), you could have a 200kw boost converter, or so.