8.2.2 Open Loop
P3.1.4.1 U/f ratio
Selection
number
Selection name Description
0 Linear
The voltage of the motor changes linearly as a function of output
frequency from zero frequency voltage (P3.1.4.6) to the field weakening
point (FWP) voltage (P3.1.4.3) at FWP frequency (P3.1.4.2) This default
setting should be used if there is no special need for another setting.
1 Squared
The voltage of the motor changes from zero point voltage (P3.1.4.6)
following a squared curve form from zero to the field weakening point
(P3.1.4.2) The motor runs undermagnetised below the field weakening
point and produces less torque. Squared U/f ratio can be used in
applications where torque demand is proportional to the square of the
speed, e.g. in centrifugal fans and pumps.
2 Programmable
The U/f curve can be programmed with three different points (see
Programmable U/f curve): Zero frequency voltage (P1), Midpoint
voltage/frequency (P2) and Fieldweakening point (P3). Programmable
U/f curve can be used if more torque is needed at low frequencies. The
optimal settings can automatically be achieved with Motor identification
run (P3.1.2.4).
U[V]
f[Hz]
Un
ID603
ID602
2
3
5
1
4
9094
Linear and squared change of motor voltage
Pos. Description
1 Default: Nominal voltage of the motor
2 Linear
3 Squared
4 Field weakening point
5 Default: Nominal frequency of the motor
131
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