Danfoss VLT AutomationDrive FC 302 Programming Manual page 147

Parameter Descriptions
14-10 Mains Failure
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 drops to about 373 V DC, and the
IGBTs cut off and loose the control of the motor.
When mains is restored, and the IGBTs start
again, the output frequency and voltage vector
do 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 according 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. Control of the motor remains with the frequency
ramp- converter, and the frequency converter performs
down a controlled ramp down from
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
bring 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:
MG33MJ02
Programming Guide
14-10 Mains Failure
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
Danfoss A/S © Rev. 10/2014 All rights reserved.
Function:
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 1 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 3.54 Kinetick Back-up
The DC level during [4] Kinetic back-up equals to
parameter 14-11 Mains Voltage at Mains Fault *
1.35.
If the mains do not return, U is maintained as
DC
long as possible by ramping the speed down
towards 0 RPM. Finally, the frequency converter
coasts.
3 3
A
t [S]
t [S]
145