Siemens SINAMICS S120 Function Manual page 585

Drive functions

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Determining the moment of inertia

For larger speed changes, the converter initially calculates the accelerating torque M

difference between the motor torque M

The moment of inertia J of the motor and load is then obtained from the accelerating torque

– and the angular acceleration α

The following conditions must be fulfilled for this calculation:

If the load estimation has taken place and the moment of inertia does not settle (stabilize)

(r1407.24/26 = 0), then increasing the acceleration (p2572/p2573) is recommended.

If the load moment of inertia is significantly greater than the motor moment of inertia, then

the transient event can also be improved via parameterization of the load moment of inertia

Drive functions

Function Manual, 11/2017, 6SL3097-4AB00-0BP5

Acceleration torque M

> than p1560 · r0333 (rated motor torque) and

> than 80 % of the friction torque (0.4 · (p1563 - p1564)).

For operation without encoder, the speed must be > p1755 (in closed-loop controlled

The converter calculates the load torque again after acceleration.

, load torque M

Function modules

8.12 Moment of inertia estimator

and frictional torque M

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