Eliminated from:
9400 HighLine Single Drive SW V7.0, sizes 1 to 7
Behaviour of the new version?
The filtering function for generating the DC-bus voltage signal can be deactivated by means of a new code C0281 (default setting: filter deactivated).
This means that the DC-bus voltage can start influencing the PWM generation process (switch-on/switch-off ratio of the IGBTs) immediately, without filtering causing any delay. Deviations between the actual DC-bus voltage and the (if applicable) filtered signal value no longer have to be compensated via the motor control, which runs in a correspondingly stable manner.
Filtering remains active for the large types 8 to 10; code C0281 has no effect on devices of this size.
Which products does the problem affects?
HighLine Single Drive SW ≤ V5.1, sizes 1 to 7
Description of the problem
The drive follows the setpoints with deviations and demonstrates torque/speed variations when voltage peaks occur in the DC bus. If monitoring thresholds have been set accordingly, following error and speed error messages will be issued.
The deviation between the actual DC-bus voltage and the filtered signal value must be compensated by the motor control, which results in the fluctuations already described.
When does the problem occur?
This behaviour has been observed in applications where the DC-bus voltage undergoes sudden changes (e.g. due to fast motor braking operations or to switching operations on the supply side). The abrupt change in the DC-bus voltage results in the motor being temporarily supplied with too little/too much power, as the PWM has not been adapted to the fluctuating DC-bus level dynamically enough. This can lead to corresponding torque variations on the drive.
Diagnostics options?
The drive demonstrates variations in both speed and torque, which are linked to fluctuations in the DC-bus voltage.
Short-term measures/recommendations?
None.
Evaluation:
The behaviour can lead to variations in the control loops of the motor control, since an input variable for generating the PWM (level of the DC-bus voltage signal) does not correspond to the actual, physical value for a short time. This behaviour is caused by the deviation between the actual DC-bus voltage and the filtered DC-bus voltage signal which is used to generate the PWM. The incorrectly calculated PWM results in the motor being supplied with power that varies slightly and so leads to fluctuations in the actual torque/actual speed value.
Published with Service Message No. 38/2009
