The motor operation characteristics during VFD regeneration, also referred to as regen are:

1. The motor flux fields as controlled by the drive are spinning in the same direction as the load that is driving it. If the shaft is being driven by the load but the inverter is not gating, no regen is captured as the stator circuit would be open.

2. Slip is negative. Note, slip is defined as:

Synchronous speed => speed of rotation of the stator induced flux field as drive by the VFD

Motor speed => Speed at which the load is driving the rotor