Siemens SINAMICS S120 Function Manual page 544

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Function modules

9.12 Moment of inertia estimator

The load torque has stabilized (settled) once one of the following conditions is satisfied.

● Condition 1:

● Condition 2:

The moment of inertia can be calculated in the acceleration phases after the load torque has

settled. The start value for the moment of inertia estimator thus corresponds with the

parameterized moment of inertia (J = p0341 · p0342 + p1498).

Remaining calculation

If the source of p1502 has a 1 signal, the moment of inertia is not estimated.

Accuracy of calculation

The accuracy of the moment of inertia estimation increases as the acceleration rate increases.

Estimating 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 M

– and the angular acceleration α

The following conditions must be satisfied to calculate the moment of inertia:

● The acceleration torque M

friction torque (0.4 · (p1563 - p1564)).

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

● The setpoint acceleration must be > 3.2 / number of pole pairs 1/s

Direction: Measurement is performed in the di‐

rection of travel.

Instant in time: Measurement is performed after

If the load was measured for a minimum duration

of 3 · p1562.

If p1563 and p1564 are entered from a previous

measurement and saved.

, load torque M

must be > p1560 · r0333 (rated motor torque) and > 80% of the

and frictional torque M

or 3.2 · pole pair width m/

Function Manual, 06/2019, 6SL3097-5AB00-0BP2

Drive functions