Danfoss VLT AutomationDrive FC 301 Programming Manual page 160

Parameter Descriptions
14-10 Mains Failure
Options [1] Ctrl. ramp-down, [2] Ctrl. ramp-down, trip, [5] Kinetic
back-up, trip, [7] Kin. back-up, trip w recovery are not active when
the option [2] Torque is selected in parameter 1-00 Configuration
Mode.
3 3
Option:
[0] No
function
*
[1] Ctrl.
ramp-
down
158
VLT
Function:
NOTICE
Parameter 14-10 Mains Failure cannot be
changed while motor runs.
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 lose 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 is reached.
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.
Control of the motor remains with the frequency
converter, and the frequency converter performs
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 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 may bring the output frequency
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
Danfoss A/S © 02/2016 All rights reserved.
®
AutomationDrive FC 301/302
14-10 Mains Failure
Options [1] Ctrl. ramp-down, [2] Ctrl. ramp-down, trip, [5] Kinetic
back-up, trip, [7] Kin. back-up, trip w recovery 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
Function:
before the motor is ramped to 0, the motor is
coasted.
Limitation:
See the introduction text in
parameter 14-10 Mains Failure.
The functionality is the same as in option [1] Ctrl.
ramp-down, except in this option a reset is
necessary for starting up after power-up.
Centrifuges can run for 1 hour without 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
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 s. Many industry
applications can extend controlled operation for
many s, 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 3.56 Kinetic 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 does not return, U
DC
as long as possible by ramping the speed down
A
t [S]
t [S]
is maintained
MG33ML02