Advanced commissioning
7.11 Motor control
SIMATIC ET 200pro FC-2 converter
164
Operating Instructions, 04/2018, FW V4.7 SP10, A5E34257324B AF
For higher speed changes, the inverter initially calculates the accelerating torque M
B
as
difference between the motor torque M
M
, load torque 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 obtained from the accelerating torque M
B
and
angular 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.
Moment of inertia precontrol
In applications where the motor predominantly operates with a constant speed, the inverter
can only infrequently calculate the moment of inertia using the function described above.
Moment of inertia precontrol is available for situations such as these. The moment of inertia
precontrol assumes that there is an approximately linear relationship between the moment of
inertia and the load torque.
Example: For a horizontal conveyor, in a first approximation, the moment of inertia depends
on the load.
Figure 7-36 Moment of inertia precontrol
The relationship between load torque and torque is saved in the inverter as linear
characteristic.
●
In a positive direction of rotation:
Moment of inertia J = p5312 × load torque M
L
+ p5313
●
In a negative direction of rotation:
Moment of inertia J = p5314 × load torque M
L
+ p5315
