Rockwell Automation Publication 7000L-UM301F-EN-P - March 2020 239
Commissioning Chapter 4
T DC Link
The tuning of the current regulator is controlled by three parameters – two in the
Current Control group, and one in the Drive Hardware group:
1. Current regulator bandwidth CurReg Bandwidth
2. DC Link time constant T DC Link
3. DC Link inductance in per unit DCLnk Induct pu
Of these three parameters, inductance DCLnk Induct pu is calculated from its
nameplate rating, the current regulator bandwidth should be set to its default
value of 200 rad/sec, and only T DC link is unknown and must be measured.
Although the current regulator was tuned during factory test, it should be
retuned during commissioning because the dc link time constant is affected by
the impedance of the drive input transformer.
The following auto-tune procedure is used to complete the rectifier side tuning:
Rectifier Auto-tuning
1. Ensure that the parameters in the Drive Hardware and Motor Ratings
groups have been set to the correct values.
2. Set parameter Autotune Select in the Autotuning parameter group to
Rectifier. The drive will go into DC Current test mode. The current
regulator bandwidth is set to Autotune Idc BW (212).
3. Start the drive. The dc current will increase to 0.2pu and stay at that level
for couple of seconds. The drive records the data under this condition and
then ramps up to approximately rated current. After staying at the level for
couple of seconds, the drive will again record the measured data and then
ramp the current to zero. The current regulator bandwidth is set back to
the original value. From the recorded data, the drive will calculate the
Autotune L Input (P217) and Autotune T DC Link (218). At the end of
the tuning Input Impedance is set to Autotune L Input and TDCLink is set
to Autotune T DC Link. During tuning if the values are determined to be
out of range, the drive will issue warnings indicated below. Try to tune the
drive again, but if the warnings persist, verify the result by tuning the drive
manually.
Warnings during Rectifier tuning and their interpretation:
L Input Low - indicates that the measured L Input is less than 0.02 pu. The L
Input must be tuned using the manual method described below.
L Input High - indicates that the measured L Input is greater than 0.5 pu. The L
Input must be tuned using the manual method described below.
T DC Link Low - indicates that the measured dc link time constant is less than
0.020 second. The step response of the current regulator should be checked using
the manual method described below.
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