Allen-Bradley PowerFlex 70 Reference Manual page 131

If the bus voltage rises above Vrecover for 20mS, the drive determines the power
loss is over. The power loss alarm is cleared.
If the drive is in a "run permit" state, the reconnect algorithm is run to match the
speed of the motor. The drive then accelerates at the programmed rate to the set
speed.
Bus Voltage
Motor Speed
Power Loss
Output Enable
Pre-Charge
Drive Fault
480V example shown, see
Decel
This mode of operation is useful if the mechanical load is high inertia and low
friction. By recapturing the mechanical energy, converting it to electrical energy
and returning it to the drive, the bus voltage is maintained. As long as there is
mechanical energy, the ride through time is extended and the motor remains fully
fluxed up. If AC input power is restored, the drive can ramp the motor to the
correct speed without the need for reconnecting.
The drive determines a power loss has occurred if the bus voltage drops below
Vtrigger.
If the drive is running, the inertia ride through function is activated.
The load is decelerated at just the correct rate so that the energy absorbed from
the mechanical load balances the losses and bus voltage is regulated to the value
Vinertia.
The Power Loss alarm in [Drive Alarm 1] is set and the power loss timer starts.
The Alarm bit in [Drive Status 1] is set if the Power Loss bit in [Alarm Config 1]
is set.
The drive faults with a F003 – Power Loss fault if the power loss timer exceeds
[Power Loss Time] and the Power Loss bit in [Fault Config 1] is set.
The drive faults with a F004 – UnderVoltage fault if the bus voltage falls below
Vmin and the UnderVoltage bit in [E238 Fault Config 1] is set.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013
Table 15 for further information.
Power Loss
680V
620V
560V
500V
407V
305V
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