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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 undervoltage level, while the inverter in 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 recovered, 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, the run command may be turned off. In consideration of such a
situation, the inverter waits 2 seconds for input of a run command after the inverter enters
ready-to-run state. If a run command is received within 2 seconds, the inverter begins the restart
processing in accordance with the data of F14 (Mode selection). If no run command has been
received within 2-second wait period, the restart mode (after a recovery from momentary power
failure) will be canceled, and the inverter 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.
In case the run commands are entered via the keypad, the above operation is also necessary for
the mode (F02 = 0) in which the direction of rotation is determined by the terminal command,
(FWD) or (REV). In the modes where the direction of rotation is fixed (F02 = 2 or 3), the direction
of rotation is retained inside the inverter, and the restart will begin as soon as the inverter enters
the ready-to-run state.
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