Danfoss VLT AutomationDrive FC 301 Programming Manual page 134

Parameter Descriptions
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:
3 3
[0] No
function
*
[1] Ctrl.
ramp-
down
[2] Ctrl.
ramp-
down,
trip
132
VLT
Function:
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. 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
14-11 Mains Voltage at Mains Fault has been
reached.
NOTICE
14-10 Mains Failure cannot be
changed while motor is running.
The frequency converter does not compensate 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.
The frequency converter remains control of the
motor and does a controlled ramp down from
14-11 Mains Voltage at Mains Fault level. If
2-10 Brake Function is [0] Off or [2] AC brake, the
ramp follows the Overvoltage Ramping. If
2-10 Brake Function is [1] Resistor Brake the ramp
follows the setting in 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
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 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.
®
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:
[3] Coasting Centrifuges can run for an hour without power
[4] Kinetic
back-up
MG33MH02 - Rev. 2013-09-30
Function:
Limitation:
See the introduction text in 14-10 Mains Failure
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
Illustration 3.53 Kinetick Back-up
A Normal operation
B Mains failure
C Kinetic back-up
D Mains return
E Normal Operation: ramping
Table 3.23 Legend to Illustration 3.53
The DC-level during [4] Kinetic back-up is
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.
If the mains return while in kinetic, back-up U
increases above 14-11 Mains Voltage at Mains
Fault*1.35. This is detected in one of the
following ways.
A
t [S]
t [S]
DC