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KFU 2-/4-
184
15 V/f-Characteristic
The sensorless control in configurations 110 and 111 is based on the proportional
change of output voltage compared to the output frequency according to the config-
ured characteristic.
By setting the V/f-characteristic, the voltage of the connected 3-phase motor is con-
trolled according to the frequency. The torque to be applied by the motor at the corre-
sponding operating point demands the control of the output voltage proportional to
the frequency. At a constant output voltage / output frequency ratio of the frequency
inverter, the magnetization is constant in the nominal operating range of the 3-phase
motor. The rating point of the motor or end point of the V/f-characteristic is set via the
guided commissioning with the parameter
Cut-off voltage
603
and the parameter
Cut-off frequency
604
.
The lower frequency range, where an increased voltage is necessary for the start of
the drive, is critical. The voltage at output frequency = zero is set with the parameter
Starting voltage
600
. An increase in voltage deviating from the linear course of the
V/f-characteristic can be defined by the parameters
Voltage rise
601
and
Rise fre-
quency
602
. The percentage parameter figure is calculated from the linear V/f-char-
acteristic. Via the parameters
Minimum frequency
418
and
Maximum frequency
419
, the working range of the machine or the V/f-characteristic is defined.
603 (UC)
601 (UK)
600 (US)
U
418 (FMIN)
419 (FMAX)
602 (FK)
604 (FC)
f
Working range
(FMIN):
Minimum frequency
418
, (FMAX):
Maximum frequency
419
,
(US):
Starting voltage
600
,
(UK):
Voltage rise
601
, (FK):
Rise frequency
602
(UC):
Cut-off voltage
603
, (FC):
Cut-off frequency
604
Parameter
Settings
No.
Description
Min.
Max.
Fact. sett.
600 Starting voltage
0.0 V
100.0 V
5.0 V
601 Voltage rise
-100 %
200 %
10 %
602 Rise frequency
0 %
100 %
20 %
603 Cut-off voltage
60.0 V
560.0 V
400.0 V
604 Cut-off frequency
0.00 Hz
999.99 Hz
50.00 Hz
Note:
The guided commissioning takes the parameterized rated motor values and
reference data of the frequency inverter into account when it comes to pre-
setting the V/f-characteristic. In the case of three-phase machines, the speed
can be increased at a constant torque if the motor winding can be switched
over from star to delta connection. If the data for delta connection indicated
on the rating plate of the three-phase motor were entered, the cut-off fre-
quency is increased automatically by the square root of three.