V/F Control Or Speed Control - Siemens SINAMICS G110M Getting Started

4.4

V/f control or speed control

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 speed 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
torque limiting.
● Torque control is only possible with vector control.
Examples of typical applications in which speed control is used:
● Hoisting gear and vertical conveyors
● Winders
● Extruders
It is not permissible to use speed control in the following cases:
● If the motor is too small in comparison to the converter (the rated motor power must not
be less than one quarter of the rated converter power)
● When you operate several motors on one converter
● When the maximum motor speed exceeds the following values:
Pole number of the motor
Maximum motor speed [rpm]
SINAMICS G110M Getting Started
Getting Started, 09/2014, FW V4.7, A5E31298643B AC
Converter pulse frequency
4.4 V/f control or speed control
2 kHz 4 kHz and higher
4-pole
4980
Commissioning
4-pole
7200
67