Selecting U/F Control Or Speed Control - Siemens SINAMICS G115D Operating Instructions Manual

Commissioning
5.3 Preparing for commissioning
5.3.3

Selecting U/f control or speed control

For reluctance motors, sensorless vector control (SLVC) is mandatory (p1300 = 20).
For asynchronous motors (2KJ8 asynchronous motors excluded), there are two different
open-loop control or closed-loop control techniques:
• U/f control (calculation of the motor voltage using a characteristic curve)
• Closed-loop speed control (i.e. field-oriented control or vector control)
For 2KJ8 asynchronous motors, sensorless vector control (SLVC) is recommended (p1300 =
20).
Criteria for selecting either U/f control or speed control
In many applications, U/f control suffices to change the speed of asynchronous motors.
Examples of typical applications for U/f control include:
• Horizontal conveyors
• Pumps
• Fans
• Compressors
When compared to U/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 (4-pole) speed exceeds the following values:
88
Maximum motor speed
Converter pulse frequency
2 kHz
4980 rpm
Operating Instructions, 09/2020, FW V4.7 SP13, A5E48681219B
4 kHz and higher
7200 rpm
SINAMICS G115D distributed drive