76
Power Loss
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. 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
V
trigger
.
If the drive is running, the inertia ride through function is activated.
The load is decelerated at the correct rate so that the energy absorbed from the
mechanical load regulates the DC bus to the value V
inertia
.
The inverter output is disabled and the motor coasts if the output frequency drops to
zero or if the bus voltage drops below V
open
or if any of the “run permit” inputs are
de-energized.
If the drive is still in inertia ride through operation when power returns, the drive
immediately accelerates at the programmed rate to the set speed. If the drive is
coasting and it 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.
Half Voltage
This mode provides the maximum power ride through. The input voltage can drop
to 50% and the drive is still able to supply drive rated current (not drive rated
power) to the motor.
!
ATTENTION:
To guard against drive damage, a minimum line
impedance must be provided to limit inrush current when the power line
recovers. The input impedance should be equal or greater than the
equivalent of a 5% transformer with a VA rating 6 times the drive’s input
VA rating.
680V
620V
560V
500V
305V
407V
Bus Voltage
Motor Speed
Output Enable
Power Loss
Pre-Charge
Drive Fault
480V example shown, see
Table F
for further information.