Motor Controllers AC Variable Frequency Drives
RVBS
Specifications are subjected to change without notice.10/08/2021
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Restart mode after momentary power failure (Basic operation)
The inverter recognizes a momentary power failure upon detecting the condition that DC link bus
voltage goes below the under-voltage detection level, while the inverter is running. If the load of the
motor is light and the duration of the momentary power failure is extremely short, the voltage drop
may not be great enough for a momentary power failure to be recognized, and the motor may
continue to run uninterrupted.
Upon recognizing a momentary power failure, the inverter enters the restart mode (after a recovery
from momentary power failure) and prepares for restart. When power is restored, the inverter goes
through an initial charging stage and enters the ready-to-run state. When a momentary power failure
occurs, the power supply voltage for external circuits such as relay sequence circuits may also drop
so as to turn the run command OFF. In consideration of such a situation, the inverter waits 2 seconds
for a run command input after the inverter enters a ready-to-run state. If a run command is received
within 2 seconds, the inverter begins the restart processing in accordance with the F12 data (Mode
selection). If no run command has been received within 2-second wait period, the inverter cancels the
restart mode (after a recovery from momentary power failure) and needs to be started again from the
ordinary starting frequency. Therefore, ensure that a run command is entered within 2 seconds after
a recovery of power, or install a mechanical latch relay.
When run commands are entered via the keypad, the above operation is also necessary for the
mode (F02 = 1) in which the rotational direction is determined by the terminal command, FWD or
REV. In the modes where the rotational direction is fixed (F02 = 2 or 3), it is retained inside the
inverter so that the restart will begin as soon as the inverter enters the ready-to-run state.
< Overall restart sequence after momentary power failure >
During a momentary power failure, the motor slows down. After power is restored, the inverter
restarts at the frequency just before the momentary power failure. Then, the current limiting function