Siemens SINAMICS S120 - Page 585

Function modules
8.12 Moment of inertia estimator
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
585
Determining the moment of inertia
For larger speed changes, the converter initially calculates the accelerating torque M
B
as the
difference between the motor torque M
M
, load torque M
L
and frictional torque M
R
:
M
B
= M
M
- M
L
- M
R
The moment of inertia J of the motor and load is then obtained from the accelerating torque
M
B
– and the angular acceleration α
J = M
B
/ α.
The following conditions must be fulfilled for this calculation:
①
Acceleration torque M
B
must be
> than p1560
· r0333 (rated motor torque) and
> than 80 % of the friction torque (0.4 · (p1563 - p1564)).
②
For operation without encoder, the speed must be > p1755 (in closed
-loop controlled
operation).
③
The converter calculates the load torque again after acceleration.
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
(p1498).