Lenze i550

10.4.3.2 Square-law V/f characterisc
The square-law V/f characterisc is typically used in heang, venlaon and climate applica-
ons to control the speed of fans and pumps.
Details
Each applicaon that is provided with the features according to the anity laws may possibly
benet from a square-law V/f characterisc.
The anity laws describe the relaon between the speed and other variables:
•
The volume ow increases proporonately to the speed.
•
The required pressure behaves proporonately to the square of the speed.
•
The power input is proporonately to the cube of the speed. This means that already a
minimal reducon of the speed may lead to substanal savings in energy consumpon.
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[%]
[%]
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100
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[%]
[%]
0 50 100
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[%]
[%]
0 50 100
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100
SpeedSpeedSpeed
Power inputPressureVolume flow
By approximaon, the square-law V/f characterisc corresponds to the curve for power input
shown above. At low frequencies, the voltage is reduced since due to the type of load a lower
voltage is sucient to generate the required power. All in all, this results in an energy-ecient
system.
Select V/f characterisc control with square-law characterisc:
1.
Motor control mode 0x2C00 (P300.00) = "V/f characterisc control (VFC open loop) [6]"
2.
V/f characterisc shape 0x2B00 (P302.00)= "Quadrac [1]"
Seng of the V/f characterisc:
•
Liming factors for the V/f characterisc are the rated mains voltage 0x2540:001
(P208.01), the minimum frequency 0x2915 (P210.00) and the maximum frequency
0x2916 (P211.00).
•
The base voltage 0x2B01:001 (P303.01) is usually set to the rated motor voltage (motor
nameplate data). The base voltage is preset to the rated mains voltage. This in turn is pre-
set according to the product key of the inverter. 4Mains voltage ^ 39
•
The base frequency 0x2B01:002 (P303.02) is usually set to the rated motor frequency
(motor nameplate data).
0
[V]
[Hz]
0
0x2540 001:
0x2B01 001:
0x2B01 002:
0x29160x2915
The current output frequency can exceed the set maximum frequency if the
gain for the slip compensaon in 0x2B09:001 (P315.01) is set to a value higher
than 0.
Conguring the motor control
V/f characterisc control for asynchronous motor (VFC open loop)
Dene V/f characterisc shape
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