Optimizing Motor Starting - Siemens SINAMICS G120 Operating Instructions Manual

Advanced commissioning
6.21 Motor control
6.21.2.2

Optimizing motor starting

After selection of the U/f characteristic, no further settings are required in most applications.
In the following circumstances, the motor cannot accelerate to its speed setpoint after it has
been switched on:
● Load moment of inertia too high
● Load torque too large
● Ramp-up time p1120 too short
To improve the starting behavior of the motor, a voltage boost can be set for the U/f
characteristic at low speeds.
Setting the voltage boost for U/f control
The inverter boosts the voltage corresponding to the starting currents p1310 ... p1312.
Figure 6-50
Preconditions
● Set the ramp-up time of the ramp-function generator to a value 1 s (< 1 kW) ... 10 s
(> 10 kW), depending on the power rating of the motor.
● Increase the starting current in steps of ≤ 5%. Excessively high values in p1310 ... p1312
can cause the motor to overheat and switch off (trip) the inverter due to overcurrent.
If message A07409 appears, it is not permissible that you further increase the value of any
of the parameters.
Procedure
1. Switch on the motor with a setpoint of a few revolutions per minute.
2. Check whether the motor rotates smoothly.
3. If the motor does not rotate smoothly, or even remains stationary, increase the voltage
boost p1310 until the motor runs smoothly.
4. Accelerate the motor to the maximum speed with maximum load.
5. Check that the motor follows the setpoint.
6. If necessary, increase the voltage boost p1311 until the motor accelerates without problem.
294
The resulting voltage boost using a linear characteristic as example
Converter with the CU250S-2 Control Units
Operating Instructions, 04/2018, FW V4.7 SP10, A5E31759476B AG