Square-Law V/F Characteristic - Lenze i55AE125B Manual

Motor control
Motor control selection
V/f characteristic control (VFC)
8.2.1.2

Square-law V/f characteristic

The square-law V/f characteristic is typically used in heating, ventilation and climate applica-
tions to control the speed of fans and pumps.
Details
Each application that is provided with the features according to the affinity laws may possibly
benefit from a square-law V/f characteristic.
The affinity laws describe the relation between the speed and other variables:
The volume flow increases proportionately to the speed.
•
The required pressure behaves proportionately to the square of the speed.
•
The power input is proportionately to the cube of the speed. This means that already a
•
minimal reduction of the speed may lead to substantial savings in energy consumption.
Volume flow
[%]
100
50
0
0 50
By approximation, the square-law V/f characteristic 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 sufficient to generate the required power. All in all, this results in an energy-efficient
system.
Select V/f characteristic control with square-law characteristic:
1. Motor control mode 0x2C00 (P300.00)
2. V/f characteristic shape
Setting of the V/f characteristic:
Limiting factors for the V/f characteristic are rated mains voltage
•
minimum frequency 0x2915 (P210.00)
The base voltage 0x2B01:001 (P303.01)
•
nameplate data). The base voltage is preset to the rated mains voltage. This again is preset
according to the product key of the inverter.
The base frequency 0x2B01:002 (P303.02)
•
(motor nameplate data).
The current output frequency can exceed the set maximum frequency if the
gain for the slip compensation in
than 0.
Next steps
The inverter provides different functions by means of which the drive behaviour can be
•
further optimised.4Optimisation of motor control
An optimisation of the control loops is not mandatory for this motor control type but may
•
lead to a better control mode.
168
Pressure
[%]
100
50
0
100 [%] 0
Speed
= "V/f characteristic control (VFC open loop) [6]"
0x2B00 (P302.00) = "Quadratic [1]"
and maximum frequency
is usually set to the rated motor voltage (motor
4Mains voltage
is usually set to the rated motor frequency
[V]
0x2540 001 :
0x2B01 001 :
0
0
0x2915
0x2B09:001 (P315.01)
4Optimisation of the control loops
Power input
[%]
100
50
0
50 100 [%] 0
Speed
0x2540:001 (P208.01),
0x2916 (P211.00).
^ 144
0x2B01 002 :
[Hz]
0x2916
is set to a value higher
^ 182
^ 193
50 100 [%]
Speed