Siemens SINAMICS G120 Operating Instructions Manual page 58

Basic commissioning
6.1 Preparing basic commissioning
Criteria for selecting either U/f control or speed control
U/f control is suitable for most applications in which the speed of induction motors is to be
changed. Examples of typical applications for U/f control include:
● Pumps
● Fan
● Compressors
● Horizontal conveyors
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.
● The full torque is possible at standstill.
● 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 inverter (the rated motor power may not be
● If several motors are connected to one inverter
● If a power contactor is used between the inverter and motor and is opened while the
● If the maximum motor speed exceeds the following values:
Pole number of the motor
Maximum motor speed [rpm]
56
less than one quarter of the rated inverter power)
motor is powered up
Inverter pulse frequency 2 kHz
2-pole 4-pole 6-pole
9960 4980 3320
SINAMICS G120C frequency converter
Operating Instructions, 03/2012, FW V4.5, A5E02999804B AB
4 kHz and higher
2-pole 4-pole 6-pole
14400 7200 4800