Siemens SINAMICS G120C Operating Instructions Manual page 214

Advanced commissioning
6.5 Motor control
Moment of inertia precontrol
In applications where the motor predominantly operates with a constant speed, the inverter
can only infrequently calculate the moment of inertia using the function described above.
Moment of inertia precontrol is available for situations such as these. The moment of inertia
precontrol assumes that there is an approximately linear relationship between the moment of
inertia and the load torque.
Example: For a horizontal conveyor, in a first approximation, the moment of inertia depends
on the load.
You have the following options to determine the characteristic:
• You already know the characteristic from other measurements. In this case, you must set
the parameters to known values when commissioning the system.
• The inverter iteratively determines the characteristic by performing measurements while
the motor is operational.
Activating the moment of inertia estimator
The moment of inertia estimator is deactivated in the factory setting. p1400.18 = 0,
p1400.20 = 0, p1400.22 = 0.
If you performed the rotating measurement for the motor identification during basic
commissioning, we recommend leaving the moment of inertia estimator deactivated.
Preconditions
● You are using a 1FK7 encoderless permanent-field synchronous motor.
● You have selected encoderless vector control.
● The load torque must be constant whilst the motor accelerates or brakes.
Typical of a constant load torque are conveyor applications and centrifuges, for example.
Fan applications, for example, are not permitted.
● The speed setpoint is free from superimposed unwanted signals.
● The motor and load are connected to each other with an interference fit.
Drives with slip between the motor shaft and load are not permitted, e.g. as a result of
loose or worn belts.
If the conditions are not met, you must not activate the moment of inertia estimator.
210
The relationship between load torque and torque
is saved in the inverter as linear characteristic.
In a positive direction of rotation:
Moment of inertia J = p5312 × load torque M
p5313
In a negative direction of rotation:
Moment of inertia J = p5314 × load torque M
p5315
Operating Instructions, 07/2015, FW V4.7 SP3, A5E34263257B AC
+
L
+
L
SINAMICS G120C converter