130 01-6203-01R3, CG Drives & Automation
7.2.1.2. Square-law V/f characteristic
The square-law V/f characteristic is typically used in heating, ventilation and climate
applications 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.
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) = "V/f characteristic control (VFC open loop)
[6]"
2. V/f characteristic shape 0x2B00 (P302.00) = "Quadratic [1]"
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