Owner's manual

Rockwell Automation Publication D2-3518-3 - May 2013 113
Chapter 9
When the inverter detects a power loss condition, it enters its power loss state and
starts the power loss timer. If the power loss timer expires before the power loss
condition ends and the Power Loss fault is enabled, then a Power Loss fault
(fault 3) occurs. The inverter only enters its power loss state when it is running.
The Power Loss fault (fault 3) is enabled and disabled using inverter
Fault Config 1 (238).
The time that the inverter remains in the power loss state before faulting, is set
using inverter Power Loss Time (185). However, if the Power Loss fault is not
enabled, then the inverter Power Loss Time parameter has no effect on the
response to and recovery from power loss.
If the Power Loss Mode is set to Coast, Continue, or Coast Input, then the
inverter handles power loss conditions in the following manner:
• As soon as the power loss condition is detected, the inverter coasts the
motor (stop applying voltage)
• If the power loss condition ends before any fault (including a Power Loss
fault) occurs, the inverter leaves the power loss state by restarting the
motor. The inverter initiates a flying start sequence in order to determine
the rotational speed of the motor, and sets the initial output frequency
based on that speed. The flying start sequence after a recovery from power
loss is not affected by the value of the inverter Flying Start En parameter
(169). If the motor is spinning in reverse at the time of the flying start
sequence and inverter Direction Mode (190) is set to Reverse Disable,
then the flying start sequence is not able to match the speed of the motor,
and 0 Hz is used as the initial output frequency.
If the Power Loss Mode is set to Decel, Decel Input, or Decel Fault, then the
inverter handles power loss conditions in the following manner:
• As soon as the power loss is detected, the inverter starts decelerating the
motor in an attempt to use the inertia of the motor to maintain the DC
bus voltage at a useful level. This is called inertial ridethrough.
• If the output frequency reaches 0 Hz, or the DC bus voltage drops so far
that it is not possible to maintain motor voltage, the inverter coasts the
motor. At this point, power loss recovery proceeds as for Coast mode,
described above. However, at the point where the motor is coasted, if the
power loss mode is set to Decel Fault and the Power Loss fault (fault 3) is
enabled, the inverter immediately faults with the Power Loss fault rather
than waiting any longer for power to come back or for the timer to expire.
• If the power loss condition ends before any fault (including a Power Loss
fault) occurs, and the inverter has been able to maintain motor voltage
through the entire power loss, the inverter exits its power loss state by
accelerating the motor up to its currently commanded speed using the
currently commanded acceleration rate.
Note that the response of the entire drive to loss of AC line synchronization is
also affected by rectifier parameters Ride Through Ena (64) and Ride Through
Sec (65).