In steady state and regenerative mode, the motor is in hypersynchronous so the energy is sent back to the main, with no problems.
The problem can be if you have a low current (close to the PHF threshold) and during the transition between motor/generator state then the residual current can be only the magnetizing current and decrease under the PHF threshold.
No energy is transferred during deceleration.
Only a little during deceleration in dynamic braking stop mode but do not take this into account because it is a very low level of energy.

Released for:Schneider Electric India