6. Optimize the controller by adapting the ratio of the moments of inertia of the load and motor
(p0342):
Initially, the speed actual value follows the speed setpoint with
some delay, and then overshoots the speed setpoint.
● Increase p0342
Initially, the speed actual value increases faster than the speed
setpoint. The setpoint passes the actual value before reaching its
final value. Finally, the actual value approaches the setpoint with‐
out any overshoot.
● Reduce p0342
7. Switch off the motor.
8. Set p0340 = 4. The inverter again calculates the speed controller parameters.
9. Switch on the motor.
10.Over the complete speed range check as to whether the speed control operates
satisfactorily with the optimized settings.
You have optimized the speed controller.
When necessary, set the ramp-up and ramp-down times of the ramp-function generator
(p1120 and p1121) back to the value before optimization.
Mastering critical applications
The drive control can become unstable for drives with a high load moment of inertia and
gearbox backlash or a coupling between the motor and load that can possibly oscillate. In this
case, we recommend the following settings:
● Increase p1452 (smoothing the speed actual value).
● Increase p1472 (integral time T
I
): T
I
≥ 4 · p1452
● If, after these measures, the speed controller does not operate with an adequate dynamic
performance, then increase p1470 (gain K
P
) step-by-step.
The most important parameters
Table 6-51 Encoderless speed control
Parameter Description
p0342 Moment of inertia ratio, total to motor (factory setting: 1.0)
p1496 Acceleration precontrol scaling (factory setting: 0 %)
For the rotating measurement of the motor data identification the inverter sets the pa‐
rameters to 100 %.
p1452 Speed controller speed actual value smoothing time (without encoder) (factory setting:
10 ms)
p1470 Speed controller operation without encoder P gain (factory setting: 0.3)
p1472 Speed controller operation without encoder integral action time (factory setting: 20 ms)
Advanced commissioning
6.19 Motor control
SINAMICS G120C converter
272 Operating Instructions, 09/2017, FW V4.7 SP9, A5E34263257B AF
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