Danfoss VLT AutomationDrive FC 302 Programming Manual page 145

Parameter Descriptions
3.15.2 14-1* Mains On/Off
Parameters for configuring mains failure monitoring and
handling. If a mains failure appears, the frequency
converter tries to continue in a controlled way until the
power in the DC link has been exhausted.
14-10 Mains Failure
Note:
Options [1], [2], [5], [7] are not active when the option [2] Torque
is selected in parameter 1-00 Configuration Mode.
Option: Function:
Parameter 14-10 Mains Failure is typically used
where very short mains interruptions (voltage
dips) are present. At 100% load and a short
voltage interruption, the DC voltage on the main
capacitors drops quickly. For larger frequency
converters it only takes a few milliseconds before
the DC level is down to about 373 V DC and the
IGBTs cut off and looses the control over the
motor. When mains is restored, and the IGBTs
start again, the output frequency and voltage
vector does not correspond to the speed/
frequency of the motor, and the result is
normally an overvoltage or overcurrent, mostly
resulting in a trip lock. Parameter 14-10 Mains
Failure can be programmed to avoid this
situation.
Select the function to which the frequency
converter must act when the threshold in
parameter 14-11 Mains Voltage at Mains Fault has
been reached.
NOTICE
Parameter 14-10 Mains Failure cannot be
changed while motor is running.
[0] No The frequency converter does not compensate
function for a mains interruption. The voltage on the DC
*
link drops quickly and motor control is lost
within milliseconds to seconds. Trip lock is the
result.
[1] Ctrl. The frequency converter remains control of the
ramp- motor and does a controlled ramp down from
down parameter 14-11 Mains Voltage at Mains Fault
level. If parameter 2-10 Brake Function is [0] Off or
[2] AC brake, the ramp follows the Overvoltage
Ramping. If parameter 2-10 Brake Function is [1]
Resistor Brake the ramp follows the setting in
parameter 3-81 Quick Stop Ramp Time. This
selection is particularly useful in pump
applications, where the inertia is low and the
friction is high. When mains is restored, the
output frequency ramps the motor up to the
reference speed (if the mains interruption is
prolonged, the controlled ramp down might take
®
VLT AutomationDrive FC 301/302 Programming Guide
14-10 Mains Failure
Note:
Options [1], [2], [5], [7] are not active when the option [2] Torque
is selected in parameter 1-00 Configuration Mode.
Option:
[2] Ctrl.
ramp-
down,
trip
[3] Coasting
[4] Kinetic
back-up
MG33MI02 - Rev. 2013-11-20
Function:
the output frequency all the way down to 0 RPM,
and when the mains is restored, the application
is ramped up from 0 RPM to the previous
reference speed via the normal ramp up). If the
energy in the DC-link disappears before the
motor is ramped to zero, the motor is coasted.
Limitation:
See the introduction text in
parameter 14-10 Mains Failure
This selection is similar to selection [1] except
that in [2] a reset is necessary for starting up
after power-up.
Limitation:
See the introduction text in
parameter 14-10 Mains Failure
Centrifuges can run for an hour without power
supply. In those situations, it is possible to select
a coast function at mains interruption, together
with a flying start which occurs when the mains
is restored.
Kinetic back-up ensures that the frequency
converter keeps running as long as there is
energy in the system due to the inertia from
motor and load. This is done by converting the
mechanical energy to the DC-link and thereby
maintaining control of the frequency converter
and motor. This can extend the controlled
operation, depending on the inertia in the
system. For fans it is typically several seconds, for
pumps up to 2 seconds and for compressors only
for a fraction of a second. Many industry
applications can extend controlled operation for
many seconds, which is often enough time for
the mains to return.
A B C D E
U [V]
DC
U
DC
14-11*1.35
n [RPM]
Ref
A Normal operation
B Mains failure
C Kinetic back-up
D Mains return
E Normal Operation: ramping
Illustration 3.53 Kinetick Back-up
3 3
A
t [S]
t [S]
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