V/F Control Or Vector Control (Speed/Torque) - Siemens SINAMICS G120 Operating Instructions Manual

5.2.5

V/f control or vector control (speed/torque)?

For induction motors, there are two different open-loop control or closed-loop control
techniques:
● V/f control (calculation of the motor voltage using a characteristic curve)
● Closed-loop speed control (also: field-oriented control or vector control)
Criteria for selecting either V/f control or vector control
In many applications, the V/f control suffices to change the speed of induction motors.
Examples of typical applications for V/f control include:
● Pumps
● Fans
● Compressors
● Horizontal conveyors
When compared to V/f control, vector control offers the following advantages:
● The speed is more stable for motor load changes.
● Shorter accelerating times when the setpoint changes.
● Acceleration and braking are possible with an adjustable maximum torque.
● Improved protection of the motor and the driven machine as a result of the adjustable
● Full torque is possible at standstill.
Examples of typical applications in which speed control is used:
● Hoisting gear and vertical conveyors
● Winders
● Extruders
It is not permissible to use vector control in the following cases:
● If the motor is too small in comparison to the converter (the rated motor power must not
● When you operate several motors on one converter
● If a power contactor is used between the converter and motor, and is opened while the
● When the maximum motor speed exceeds the following values:
Converter with the CU250S-2 Control Unit (vector)
Operating Instructions, 06/2013, FW V4.6, A5E31759476B AB
torque limiting.
be less than one quarter of the rated converter power)
motor is powered up
Converter pulse frequency
Pole number of the motor
Maximum motor speed [rpm]
5.2 Preparing for commissioning
2 kHz
2-pole 4-pole 6-pole
9960 4980 3320
Commissioning
4 kHz and higher
2-pole 4-pole 6-pole
14400 7200 4800
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