Closed-loop thyristor current control
5-64 System- and communication configuring D7-SYS - SIMADYN D
Edition 06.2002
PA6.NCM = 2: The line supply period is converted into an internal line
supply value. From the last (max. 8) line supply values, the number of
which is defined at PA6.FAM, the average value is generated and
transferred to the synchronizing function. The average value is
continuously generated {1 ≤ PA6.FAM ≤ 8}.
This means that changes in the line supply value appear smooth for the
internal monitoring. This allows low frequency fluctuations to be
suppressed using an n x duration of the line supply periods
(e.g. a 12.5 Hz fluctuation does not appear in the frequency-dependent
quantities when using an average value generated over 4 values).
PA6.NCM = 3: Period and therefore line supply value fluctuations are
corrected using the PLL method (P controller). The phase difference is
only taken into account with 1/FAM. {1 ≤ PA6.FAM ≤ 1000}.
PA6.NCM = 4: Period and therefore line supply value fluctuations are
corrected using the PLL method (PI controller). The phase difference is
weighted only with 1/FAM and the last average with (FAM-1)/FAM.
NCM=4 with FAM=20…40 is most suitable for single, one-off faults of the
synchronizing voltage.
• The average value generation of the line supply period must be
adapted to the line frequency fluctuation by making a suitable entry at
PA6.FAM.
• Trace several periods of the non-averaged line supply frequency
(connection PA6.XFN, actual frequency)
Determine the factor n:
duration periodsupply Line
nfluctuatio theofduration Period
=n
NOTE
If the line supply values are smoothed, this reduces the probability that
the system oscillates, but it can also mean that the gating unit becomes
slower (dynamic response) when synchronizing for real (e.g. load-
related) frequency dips and then shuts-down with a pulse position
error.
Separate sensing is required for more significant fluctuations of the line
supply voltage at the power feed.
The normalized signal is connected to connection EMF.AAV and corrects
the gating unit firing angle.
5.4.3 Communications utility, time synchronization
All of the time functions (FB RTC…) cannot be used when using the
closed-loop thyristor current control in conjunction with the ITDC
expansion module.
In order that the time-critical closed-loop current control is not interrupted
by "external" interrupts (clock interrupts), then these interrupts are
suppressed by programming FBs on the processor. This means that the
time utility is no longer available!
Line supply voltage
fluctuations
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