Siemens SINAMICS G120D Series Operating Instructions Manual page 160

Advanced commissioning
7.5 Motor control
Calculating the load torque
Calculating the moment of inertia
If all of the following conditions are met, the inverter calculates the moment of inertia:
①
•
– The sign of M
– M
②
•
• The inverter has calculated the load torque in at least one direction of rotation.
• Acceleration setpoint > 8 1/s
③
The inverter calculates the load torque again after acceleration.
160
The rated accelerating torque M
is the same as the direction of the actual acceleration
B
> p1560 × rated motor torque (r0333)
B
speed > p1755
At low speeds, the inverter calculates the load torque
M from the actual motor torque.
L
The calculation takes place under the following con-
ditions:
• Speed ≥ p1226
• Acceleration setpoint < 8 1/s
480 rpm per s)
• Acceleration × moment of inertia (r1493) < 0.9 ×
p1560
For larger changes, the inverter initially cal-
culates the accelerating torque M
ence between the motor torque M
torque M
M = M
B
The moment of inertia J of the motor and
load is then obtained from the accelerating
torque M
(α = rate of change of speed):
J = M
B
must satisfy the following two conditions:
B
(≙ speed change 480 rpm per s)
2
Operating Instructions, 04/2015, FW V4.7.3, A5E34262100B AB
(≙ speed change
2
and frictional torque M
L
- M - M
M L R
– and the angular acceleration α
B
/ α
Converter with control units CU240D-2
as differ-
B
, load
M
:
R