Emerson Powerdrive F300 Reference Manual page 99

Under-voltage system
The under-voltage system controls the state of Under Voltage Active (10.016) which is then used by the sequencer state machine. Each under voltage
threshold detection system includes hysteresis of 5% of the actual threshold level therefore:
D.c. Bus Voltage (05.005)
Vdc
Threshold ≤ Vdc
Vdc ≥ Threshold x 1.05*
* Hysteresis is 5% subject to a minimum of 5V
When Under Voltage Active (10.016) = 1 the sequencer state machine will change to the UNDER_VOLTAGE state and when the UNDER_VOLTAGE
state is active it is not possible to enable the drive inverter. The under-voltage system operates in different ways depending on the setting of
Backup Supply Mode Enable (06.068).
If the low under-voltage threshold is used or if back-up supply mode is selected the internal drive power supplies are normally powered from the 24V
supply input (i.e. Digital I/O 13). See User Supply Select (06.072) for details. (It should be noted that in Regen mode Backup Supply Mode Enable
(06.068) is not present, and so back-up supply mode cannot be selected.)
Drive frame sizes 06 and below use a charging system based on a charge resistor and shorting relay. For larger drive frame sizes a thyristor based
charge system is used. The type of charge system does not alter the operation of the drive except for the times allowed for soft-start state changes and
the method used for back-up supply mode. The setting for the under-voltage level is used to detect the under-voltage condition based on the d.c. link
voltage. If a thyristor charging system is used this level is also passed to the thyristor rectifier system so that it is fully deactivated (i.e. the thyristors are
phased forwards so that the drive can take power from the supply) by the time the d.c. link voltage reaches the under-voltage level and allows the drive
inverter to become active. It should be noted that the under-voltage threshold used with a thyristor based charge system and the charging rate
(Slow Rectifier Charge Rate Enable (06.071)) are automatically saved within the rectifier units each time the value is changed because these will be
required at the next power-up before the drive control system is active. These values will be retained when they are changed 128 times. If any more
changes are made between power-up and power-down the new values are not retained.
Standard mode: Backup Supply Mode Enable (06.068) = 0
If Low Under Voltage Threshold Select (06.067) = 0 then the under voltage threshold is defined by Standard Under Voltage Threshold (06.065). If
Low Under Voltage Threshold Select (06.067) = 1 then the under voltage threshold is defined by Low Under Voltage Threshold (06.066). For drives
which have a d.c. link charge system based on a charge resistor and shorting contactor, the charge system is normally active (contactor open) when
Under Voltage Active (10.016) = 1, and inactive when Under Voltage Active (10.016) = 0. The exception is that there is a delay of 50ms while the
contactor changes state and during these periods Under Voltage Active (10.016) = 1.
If the d.c. link voltage is above the under-voltage threshold and Under Voltage Active (10.016) = 0 a large surge of current can occur if the a.c. supply is
removed and then reapplied to the drive. For a given level of supply voltage the worst case surge occurs when the supply is applied at the point where
one of the line voltages is at its peak. The surge is proportional to the difference between the d.c. link voltage before the supply is reconnected and the
magnitude of the supply voltage. The minimum setting and default for Standard Under Voltage Threshold (06.065) corresponds to the lowest d.c. link
voltage level where the maximum allowed a.c. supply voltage can be applied without damaging the drive or rupturing the recommended supply fuses.
Therefore it is safe to adjust the under-voltage threshold using the Standard Under Voltage Threshold (06.065). If the under-voltage threshold needs to be
lower than the minimum of Standard Under Voltage Threshold (06.065), then the Low Under Voltage Threshold (06.066) should be used. It is important
that the difference between the under-voltage threshold level and the peak of the supply voltage is never larger than the difference between the minimum
Standard Under Voltage Threshold (06.065) and the peak of the maximum allowed a.c. supply voltage for the drive. For example:
The minimum Standard Under Voltage Threshold (06.065) for a 400V drive is 330V
The maximum allowed supply voltage for this drive is 480V + 10%
Powerdrive F300 Parameter Reference Guide
Issue: 01.15.00
Under voltage detection
Active
No change
Not active
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