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The moment of inertia J of the motor and load is then obtained from the accelerating torque
M
and angular acceleration α (α = rate at which the speed changes):
B
J = M
If all of the following conditions are met, the converter calculates the moment of inertia:
①
•
– The sign of M
– M
②
•
• The converter has calculated the load torque in at least one direction of rotation.
• Acceleration setpoint > 8 1/s
③
The converter calculates the load torque again after acceleration.
Moment of inertia precontrol
In applications where the motor predominantly runs at constant speed, the converter can
rarely 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.
Figure 14-157
The relationship between load torque and torque is stored as a linear characteristic in the
converter.
• In positive direction of rotation:
Moment of inertia J = p5312 × load torque M
• In 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 the known values when commissioning the system.
• The converter iteratively determines the characteristic by performing measurements during
motor operation.
Parameters
The following list contains the parameters of the "Moment of inertia estimator" function.
SINAMICS G220 converter
Operating Instructions, 04/2024, FW V6.2, A5E51781573B AB
/ α
B
The measured accelerating torque M
is the same as the direction of the actual acceleration
B
> p1560 × rated motor torque (r0333)
B
Speed > p1755
Moment of inertia precontrol
must satisfy the following two conditions:
B
(≙ speed change 480 rpm per s)
2
+ p5313
L
+ p5315
L
Functions
14.10 Closed-loop drive control
559
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