Siemens SINAMICS G120C USS/MB - Page 277

When using the moment of inertia estimator, we recommend that you also activate the friction
characteristic.
Friction characteristic (Page 274)
Calculating the load torque
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At low speeds, the inverter calculates the load torque
M
L
from the actual motor torque.
The calculation takes place under the following condi‐
tions:
● Speed ≥ p1226
● Acceleration setpoint < 8 1/s
2
(≙ speed change
480 rpm per s)
● Acceleration × moment of inertia (r1493) < 0.9 ×
p1560
Calculating the moment of inertia
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For higher speed changes, the inverter initially
calculates the accelerating torque M
B
as differ‐
ence between the motor torque M
M
, load tor‐
que M
L
and frictional torque M
R
:
M
B
= M
M
- M
L
- M
R
Moment of inertia J of the motor and load is ob‐
tained from the accelerating torque M
B
and angu‐
lar acceleration α (α = rate at which the speed
changes):
J = M
B
/ α
If all of the following conditions are met, the inverter calculates the moment of inertia:
● ① The rated accelerating torque M
B
must satisfy the following two conditions:
– The sign of M
B
is the same as the direction of the actual acceleration
– M
B
> p1560 × rated motor torque (r0333)
● ② speed > p1755
● The inverter has calculated the load torque in at least one direction of rotation.
● Acceleration setpoint > 8 1/s
2
(≙ speed change 480 rpm per s)
③ The inverter calculates the load torque again after acceleration.
Advanced commissioning
6.19 Motor control
SINAMICS G120C converter
Operating Instructions, 09/2017, FW V4.7 SP9, A5E34263257B AF 277