WEG CFW501 V1.8X, Programming Manual, Page: 77 / 192

V/f Scalar Control
CFW501 | 9-1
9
9 V/f SCALAR CONTROL
This is the classical control method for three-phase induction motors, based on a curve that relates output
frequency and voltage. The inverter works as a variable frequency voltage source, generating a combination of
voltage and frequency according to the configured curve. It is possible to adjust this curve for standard 50 HZ or
60 HZ or special motors.
According to the block diagram of Figure 9.1: Block diagram of V/f scale control on page 9-2 , the speed reference
f* is limited by P0133 and P0134 and applied to the input of “V/f CURVE” block input, where the output voltage
amplitude and frequency imposed to the motor are obtained. For further details on the speed reference, refer to
chapter 7 LOGICAL COMMAND AND SPEED REFERENCE on page 7-1 .
By monitoring the total and active output current, and the DC link voltage, compensators and controllers which
help protect the V/f control performance are implemented. The operation and parameterization of those blocks
are detailed in
section 11.2 - DC Link Voltage and Output Current Limitation .
The advantage of the V/f control is its simplicity and the need of few settings. The start-up is quick and simple
and the factory default, and the factory default normally requires little or no modification. Besides, in cases where
the application allows the proper adjustments of the V/f curve, you save energy.
The V/f or scalar Control is recommended for the following cases:
„
Drive of several motors with the same inverter (multi-motor drive).
„
Energy saving in the drive of loads with quadratic torque/speed relationship.
„
Motor rated current lower than 1/3 of the inverter rated current.
„
For test purposes, the inverter is turned on without motor or with a small motor with no load.
„
Applications where the load connected to the inverter is not a three-phase induction motor.