Overcurrent Protection; Limiting The Maximum Dc Link Voltage - Siemens SINAMICS G120 Operating Instructions Manual

Setting functions
8.6 Protection functions
8.6.3

Overcurrent protection

During vector control, the motor current remains within the torque limits set there.
During V/f control, the maximum current controller (I-max controller) protects the motor and
converter against overload by limiting the output current.
I-max controller operation
If an overload situation occurs, the speed and stator voltage of the motor are reduced until
the current is within the permissible range. If the motor is in regenerative mode, (i.e. it is
being driven by the connected machine), the I-max controller increases the speed and stator
voltage of the motor to reduce the current.
Note
The converter load is only reduced if the motor torque decreases at lower speeds (e.g. for
fans).
In the regenerative mode, the current only decreases if the torque decreases at a higher
speed.
Settings
You only have to change the factory settings of the I-max controller if the drive tends to
oscillate when it reaches the current limit or it is shut down due to overcurrent.
Table 8- 25
Parameter
p0305
p0640
p1340
p1341
r0056.13
r1343
For more information about this function, see function diagram 1690 in the List Manual.
8.6.4

Limiting the maximum DC link voltage

How does the motor generate overvoltage?
An induction motor operates as a generator if it is driven by the connected load. A generator
converts mechanical power into electrical power. The electrical power flows back into the
inverter and causes V
258
I-max controller parameters
Description
Rated motor current
Motor current limit
Proportional gain of the I-max controller for speed reduction
Integral time of the I-max controller for speed reduction
Status: I-max controller active
Speed output of the I-max controller
Shows the amount to which the I-max controller reduces the speed.
in the inverter to increase.
DC
Converter with the CU250S-2 Control Unit (vector)
Operating Instructions, 06/2013, FW V4.6, A5E31759476B AB