108 U/F RATIO SELECTION 234567 (2.6.3)
Table 105: Selections for parameter ID108
Selection
number
Selection name Description
0 Linear
The voltage of the motor changes linearly as a function of the
output frequency. The voltage changes from the value of
Zero Frequency Voltage (ID606) to the value of Voltage at
Field Weakening Point (ID603) at a frequency set in Field
Weakening Point Frequency (ID602). Use this default setting
if a different setting is not necessary.
1 Squared
The voltage of the motor changes from the value of Zero Fre-
quency Voltage (ID606) to the value of Field Weakening Point
Frequency (ID603) at a squared curve. The motor operates
undermagnetised below the field weakening point and pro-
duces less torque. You can use the squared U/f ratio in appli-
cations where the torque demand is in relation to the square
of the speed, for example in centrifugal fans and pumps. See
Fig. 24.
2 Programmable
It is possible to program the U/f curve with 3 different points:
the zero frequency voltage (P1), the midpoint voltage/
frequency (P2), and the field weakening point (P3). You can
use the programmable U/f curve at low frequencies if it is
necessary to have more torque. You can find the optimal set-
tings automatically with an identification run (ID631). See
Fig. 25.
3 Linear with flux optimisation
The AC drive starts to search for the minimum motor current
in order to save energy and to lower the motor noise. This
function can be used in applications such as fans, pumps etc.
VACON · 236 PARAMETER DESCRIPTIONS
8
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