**Volt Motor Regen Simulation**
“What is efficiency of regenerative braking?”

Refer to post

http://gm-volt.com/forum/showthread.php?t=719 which shows the estimated efficiency vs. deceleration curve. I attached the model curve below for convenience.

“And, does the brake pedal have to be depressed to use it?”

All EVs with regen use a four-quadrant motor controller system. The quadrants are defined by +- Torque and +- speed –(relative to the motor synchronous speed). Refer to the attached plot for a hypothetical Volt Motor/Controller Plot. Assume the motor is outputting 100 lbf ft of

[email protected] RPM at the commanded motor drive frequency f1, as shown by the black curve. The break is applied, and the system controller’s algorithm tells the motor to go to the slower frequency f2 (blue dotted curve). The speed (2500 RPM) cannot instantaneously change, so the torque characteristic drops to -100 lbf ft at the commanded f2, which is deceleration, and the motor controller then chops and stores this energy to the battery. The breaking/regen continues as long as there is kinetic energy to convert, torque < 0, the driver applies the break, and the system controller’s algorithm commands it.

“Approximately how much charge to we regenerate on the downhill, compared to the charge we used on the uphill?”

This depends on the kinetic energy, speed/wind drag, road grade, deceleration, and system controller’s algorithm. Again, refer to the above post to get some sense of the effects of these variables. Given a profile, e.g. Highway Driving with road grade, we could use the Volt Simlulation to plot the resulting regen response during commanded deceleration.