8.7 Protection functions
The I-max controller influences the output frequency and the motor voltage.
If the motor current reaches the current limit during acceleration, the I-max controller extends
the acceleration operation.
If the load of the motor is so large during stationary operation that the motor current reaches
the current limit, the I-max controller reduces the speed and the motor voltage until the motor
current is in the permissible range again.
If the motor current reaches the current limit during deceleration, the I-max controller extends
the deceleration operation.
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 if it is shut down due to overcurrent.
Table 8- 16
For more information about this function, see function diagram 6300 in the List Manual.
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 energy into electrical energy. The electrical energy flows back into the
inverter. If the inverter cannot dissipate the electrical energy, for example in a braking
resistor, then the DC link voltage Vdc increases in the inverter.
Above a critical DC-link voltage both the inverter and the motor will be damaged. Before the
voltage can reach critical levels, however, the inverter switches the motor off with the fault
message "DC-link overvoltage".
I-max controller parameters
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.
SINAMICS G110M Operating Instructions
Operating Instructions, 04/2015, FW V4.7.3, A5E31298649B AD