Rockwell Automation DC3R Regenerative DC Drive User Guide 1/4 - 2 HP, 115/230 VAC - Manual (Page 51)

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Regenerative Drives
Figure 25. Four Quadrant Operation
Most non-regenerative, variable speed, DC drives control current flow to a
motor in one direction. The direction of torque is the same direction as the
motor rotation. Non-regenerative drives operate in Quadrant 1, and also in
Quadrant 3 if the drive is reversible (see Figure 25). Motors must stop
before reversing direction. Unless dynamic braking is used, non-
regenerative drives cannot oppose an overhauling load, and cannot
decelerate a load faster than coasting to a lower speed.
Regenerative drives operate in two additional quadrants: Quadrant 2 and
Quadrant 4. In these quadrants, motor torque is in the opposite direction of
motor rotation.
Regenerative drives can reverse a motor without contactors, switches,
brake resistors, and inhibit plugs. They can also control an overhauling
load and decelerate a load faster than it would take to coast to a lower
speed.