Siemens SINAMICS G120 Operating Instructions Manual page 295

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.
In a negative direction of rotation:
Moment of inertia J = p5314 × load torque M
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 quick
commissioning, we recommend leaving the moment of inertia estimator deactivated.
Preconditions
● 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.
Converter with the CU240B-2 and CU240E-2 Control Units
Operating Instructions, 01/2017, FW V4.7 SP6, A5E34259001B AD
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
+ p5315
L
Advanced commissioning
6.18 Motor control
+ p5313
L
295