1-14 Functional Description
7000-TD002A-EN-P – September 2007
Line Converter Feedback The function of the line converter feedback block is to process (scale
and filter) the liner side voltage and current feedback signals to the
form required by the drive control software. The circuitry for
realizing this is built in the Analog Control Board (ACB).
The first Voltage Sensing Board (VSB) provides three line voltage
feedback signals (V
2u
, V
2v
, V
2w
), the second VSB provides two dc
(V
L+
, V
L-
) and one line side filter capacitor voltages referenced to
ground. The three line-to-ground voltages are subtracted from each
other to produce the three line-to-line voltages (V
2uv
, V
2vw
, V
2wu
). Two
of those line voltages (V
2uv
, V
2vw
) are filtered and sampled by
software for synchronization and protection. The three line voltages
are used to find the peak input voltage (V
2-pk
). This value is then
compared with trip setting (V
ltrp
) for instantaneous hardware ac over
voltage protection. In PWM drives, the neutral point of the line filter
capacitor is measured (V
n1
) and used for line side neutral over
voltage protection. The two dc voltages are subtracted to determine
the line side dc link voltage (V
dcr1
), which is then sampled by the
drive.
Current transformers (CT) in two of the ac input lines provide the
input line current feedback (I
2u
, I
2w
). Inverting and adding the two
current feedback signals reproduces the current in the remaining
phase. A Hall Effect Current Sensor (HECS) is used for monitoring
the dc link current and used for hardware overcurrent protection. In
addition the average value of the dc link current feedback is
measured using a V-f converter and used by the dc link current
controller to calculate the firing angle for the rectifier.
The preceding description applies to 6-SCR and PWM rectifier
options. For drives with the 18 pulse front-end, another VSB is daisy
chained with the first one providing additional six line-to-ground
voltages from the slave bridges. The slave 1 voltages are monitored
using (V
3uv
, V
3vw
, V
3wu
) while slave 2 voltage are monitored using
(V
4uv
, V
4vw
, V
4wu
). In addition current feedback from slave bridges I
3u
,
I
3w
and I
4u
, I
4w
are also brought in for protection. As in 6-pulse drives,
inverting and adding the two current feedback signals reproduces the
current in the remaining phase. Also for 18-pulse drives, the three ac
line-to-ground voltages are summed together to determine the neutral
to ground voltage on the input transformer.
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