Dear experts,

I am facing an issue during the commissioning of a Sinamics DCM in 2Q mode (6RA8087-6DS22-0AA0) driving a Siemens DC motor 1GG6256-0NF46-1WV1 in field weakening.

During commissioning I performed:

• armature identification,
• field excitation identification,
• flux-weakening characteristic identification.
• Speed Controller optimization

After the automatic identification the motor could run in field-weakening disconnected from the load.

After we connected the motor to load it could not reach even the nominal speed (1660 rpm). The current was only around 400A.
I manually recorded the field-weakening curve according to the document in the zip file. With these settings, the motor now enters field-weakening range, but it behaves with oscillations (see in archive attached pictures from the trace and the starter archive).

To reduce these oscillations, I lowered the EMF controller gain to very small values and set a very large integration time. However, this does not seem to be an optimal solution, because the behavior is still unstable in the field-weakening range.

To mention is that until the nominal speed of the motor it runs very smoothly without setpoint deviations.

My question is:
How can I properly tune the drive (or other relevant parameters) to eliminate the oscillations while maintaining the required performance in the field-weakening range?

Operating condition: Maximum required speed is 1910 rpm.

Thank you in advance for your support!