Danfoss VLT Midi Drive FC 280 Programming Manual page 84

Parameter Descriptions
14-10 Mains Failure
Option:
[4] Kinetic
back-up
4 4
82
Function:
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 s 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 4.17 Kinetic Back-up
The DC-level during [4] Kinetic back-up is
parameter 14-11 Mains Voltage at Mains Fault x
1.35.
If the mains does not return, U
DC
long as possible by ramping the speed down
towards 0 RPM. Finally, the frequency converter
coasts.
If mains returns while in kinetic back-up, U
increases above parameter 14-11 Mains Voltage at
Mains Fault x 1.35. This is detected in 1 of the
following ways:
•
If U >parameter 14-11 Mains Voltage at
DC
Mains Fault x 1.35 x 1.05
•
If the speed is above the reference. This
is relevant if mains comes back at a
lower level than before, for example,
parameter 14-11 Mains Voltage at Mains
Fault x 1.35 x 1.02. This does not fulfill
the criterion above, and the frequency
converter tries to reduce U
parameter 14-11 Mains Voltage at Mains
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®
VLT Midi Drive FC 280
14-10 Mains Failure
Option:
[5] Kinetic
back-up,
trip
A
t [S]
t [S]
is maintained as
[6] Alarm
[7] Kin.
back-up,
trip w
DC
recovery
14-11 Mains Voltage at Mains Fault
Range:
342 V
*
to
DC
Function:
Fault x 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
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 4.18 Kinetic Back-up Trip
Function:
[100 - This parameter defines the threshold voltage
800 V] at which the selected function in
parameter 14-10 Mains Failure is activated.
The detection level is at a factor sqrt
value in this parameter.
C D
t [S]
t [S]
2 of the
MG07C302