Danfoss iC2 Application Manual page 112

Application Guide | iC2-Micro Frequency Converters
Selection number Selection name
4 Kinetic Back-up
5 Kinetic Back-up, Trip
112
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Selection description
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.
The DC-level during [4] Kinetic backup is P 2.3.7 Power Loss
Controller Limit x 1.35. If the mains does not return, UDC is
maintained as long as possible by ramping the speed down
towards 0 RPM. Finally, the frequency converter coasts. If mains
returns while in kinetic backup, UDC increases above P 2.3.7
Power Loss Controller Limit x 1.35. This is detected in 1 of the
following ways:
• If UDC > P 2.3.7 Power Loss Controller Limit 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, P 2.3.7
Power Loss Controller Limit x 1.35 x 1.02. This does not fulfill
the criterion above, and the frequency converter tries to
reduce UDC to P 2.3.7 Power Loss Controller Limit 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 avoids the speed from going
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 backup 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.
AB413939445838en-000301 / 130R1254