Danfoss VLT AutomationDrive FC 360 Programming Manual page 92

Parameter Descriptions
14-10 Mains Failure
Option:
[2] Ctrl.
ramp-
down,
trip
4 4
[3] Coasting
[4] Kinetic
back-up
90
Function:
the DC-link disappears before the motor is
ramped to zero, the motor is coasted.
This selection is similar to selection [1] except that
in [2] a reset is necessary for starting up after
power-up.
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 4.25 Kinetick Back-up
The DC-level during [4] Kinetic back-up is
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.
If mains return while in kinetic back-up, U
increases above parameter 14-11 Mains Voltage at
Mains Fault*1.35. This is detected in one of the
following ways.
Danfoss A/S © Rev. 2014-03-31 All rights reserved.
Programming Guide
14-10 Mains Failure
Option:
[5] Kinetic
back-up,
trip
A
t [S]
t [S]
[6] Alarm
[7] Kin.
back-up,
DC
trip w
recovery
Function:
•
If U > parameter 14-11 Mains Voltage at
DC
Mains Fault*1.35*1.05
•
If the speed is above the reference. This
is relevant if mains come back at a lower
level than before, e.g.
parameter 14-11 Mains Voltage at Mains
Fault*1.35*1.02. This does not fulfil the
criterion in point one and the frequency
converter tries to reduce U
parameter 14-11 Mains Voltage at Mains
Fault*1.35 by increasing the speed. This
does not succeed as mains cannot be
lowered.
•
If running motoric. The same mechanism
as in the previous point, but where the
inertia prevents that the speed goes
above the reference speed. This leads to
the motor running motoric until the
speed is above the reference speed and
the above situation occurs. Instead of
waiting for that, the present criterion is
introduced.
The difference between kinetic back-up with and
without trip is that the latter always ramps down
to 0 RPM and trips, regardless of whether mains
return or not.
The function is made so that it does not even
detect if mains return, this is the reason for the
relatively high level on the DC-link during ramp
down.
A B C
U [V]
DC
790 V
U DC
14-11*1.35
n [RPM]
Ref
0
A Normal Operation
B Mains failure
C Kinetic back-up
D Trip
Illustration 4.26 Kinetic Back-up Trip
to
DC
D
t [S]
t [S]
MG06C402