Advanced commissioning
7.5 Motor control
Friction characteristic
Function
In many applications, e.g. applications with geared motors or belt conveyors, the frictional
torque of the load is not negligible.
The inverter provides the possibility of precontrolling the torque setpoint, bypassing the
speed controller. The precontrol reduces overshooting of the speed after speed changes.
Figure 7-23 Precontrol of the speed controller with frictional torque
The inverter calculates the current frictional torque from a friction characteristic with 10
intermediate points.
Figure 7-24 Friction characteristic
The intermediate points of the friction characteristic are defined for positive speeds. In the
negative direction of rotation, the inverter uses the intermediate points with a negative sign.
Recording a friction characteristic
After basic commissioning, the inverter sets the speeds of the intermediate points to values
suitable for the rated speed of the motor. The frictional torque of all intermediate points is still
equal to zero. On request, the inverter records the friction characteristic: The inverter
accelerates the motor step by step up to the rated speed, measures the frictional torque und
writes the frictional torque into the intermediate points of the friction characteristic.
The motor is permitted to accelerate up to the rated speed without endangering persons or
property.
To record the friction characteristic, proceed as follows:
1. Set P3845 = 1: The inverter accelerates the motor successively in both directions of
rotation and averages the measurement results of the positive and negative directions.
2. Switch on the motor (ON/OFF1 = 1).
Converter with control units CU240D-2
Operating Instructions, 04/2015, FW V4.7.3, A5E34262100B AB
157
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