This option, which is also provided by some manufacturers of VFDs, uses the energy stored in the mechanical load to keep the DC bus voltage from dropping down to the trip level. This is accomplished by running the inverter section during a voltage sag at a frequency slightly below the motor frequency, causing the motor to act as a generator. Similar to the flying restart option, the motor speed will drop while it is acting as a generator, however, the advantage is that the motor is never disconnected from the drive. This option works best for those high-inertia loads.

In Altivar drives a similar function like the Kinetic buffering function is available, the parameter named control stop on power loss, attached is the extracted page of the programming manual that has the details about the setting of the Under V.prevention (StP) parameter. When selected StP=MMS, the stop mode uses the inertia to maintain the DC bus voltage as long as possible.

Released for: Schneider Electric India