14-03 Overmodulation
Option:
Function:
[0]
Off
Selects no overmodulation of the output voltage in order to avoid torque ripple on the motor shaft.
[1] *
On
The overmodulation function generates an extra voltage of up to 8% of U
max
output voltage without
overmodulation, which results in an extra torque of 10–12% in the middle of the oversyncronous
range (from 0% at nominal speed rising to approximately 12% at double nominal speed).
14-04 PWM Random
Option:
Function:
[0] *
Off
No change of the acoustic motor switching noise.
[1]
On
Transforms the acoustic motor switching noise from a clear ringing tone to a less noticeable ‘white’
noise. This is achieved by slightly and randomly altering the synchronism of the pulse width modu-
lated output phases.
3.14.3 14-1* Line Power On/Off
Parameters for configuring line failure monitoring and handling.
14-10 Line Failure
Option:
Function:
Select the function at which the adjustable frequency drive must act, when the threshold set in par.
14-11
has been reached or a
Line Failure Inverse
command is activated
via one of the digital inputs (par. 5-1*).
[0] *
No function
The energy left in the capacitor bank will be used to "drive" the motor, but will be discharged.
[1]
Ctrl. ramp-down
The adjustable frequency drive will perform a controlled ramp-down. par.2-10
must
be set to
Off
[0].
[3]
Coasting
The inverter will turn off and the capacitor bank will back up the control card, thus ensuring a faster
restart when line power is reconnected (for short power zags).
[4]
Kinetic backup
The adjustable frequency drive will ride through by controlling speed for generative operation of
the motor utilizing the moment of inertia of the system as long as sufficient energy is present.
NOTE!
For best performance of controlled ramp-down and kinetic back-up, par.1-03
should be set to
Compressor
[0]
or
Variable Torque
[1] (no automatic energy optimization should be active).
Figure 3.2: Controlled ramp-down - short line failure. Ramping down to stop, followed by ramping up to reference.
VLT
®
HVAC Drive Programming Guide
3 Parameter Description
MG.11.C6.22 - VLT
®
is a registered Danfoss trademark
3-135
3