IEEE PES T&D Conference & Exposition 2022 - 103

Overall, these results validated the flicker mitigation
control mode using feeder voltage feedback only for use in
the field. As previously mentioned, the mode can use either
voltage feedback, grid current feedback, or a combination
to perform the mitigation. In HIL simulation and lab testing
using the combined voltage and current feedback, mitigation
percentages of up to 82% were recorded in this same
test procedure.
Field Validation and Mitigation
Power Quality Compensator Installation
A field installation of a 1MVAR power quality compensator
on a distribution network used primarily for voltage regulation
and flicker mitigation is shown in Figure 7. This installation
is tied to the PCC of a multi-MW PV plant on a rural 12.5kV
distribution grid in the eastern United States. This unit can be
remotely parameterized and controlled by the utility through
DNP3 ethernet communications to start/stop, adjust the voltage
setpoint, provide a constant reactive power command, or
enable and disable various control modes.
Field Performance
A power quality meter on-site at the output of a power quality
compensator installation provided real-time and trending
data showing the effectiveness in solving voltage regulation
and flicker issues. An example of the steady-state voltage
regulation at the PCC of the PV plant is shown in Figure 8.
In the top subplot of Figure 8 in blue, the line-to-line voltage
is shown on a per-unit basis without the power quality
compensator. For a similar day of PV production, the voltage
with the power quality compensator is shown in red. The
system was parameterized with a voltage reference of 1.02pu
and a dead-band of +/−0.004pu, shown in black and dashed
green lines on the top subplot, respectively. With the compensator
on, the voltage stays on the edge of the dead-band,
minimizing the kvar output throughout the day while still
adhering to the programmed setpoints. The bottom subplot
shows the kvar output of the power quality compensator
throughout that same day. This follows the classic PV " duck "
curve typically referred to when discussing renewable power
generation. The compensator absorbs VARs throughout the
day to pull down the grid voltage, and as the sun goes down
and the load on the grid increases, it provides positive kvar
to boost the voltage. During the evening and early morning,
kvar output/absorption of the power quality compensator is
kept to a minimum as the PV production is limited.
In addition to voltage regulation, the power quality compensator
at this site is also tasked with flicker mitigation.
The power quality meter reports trends of instantaneous
flicker, short-term flicker, and long-term flicker based on
IEC flicker measurement standards. Figure 9 below shows a
weeklong trend of flicker values two weeks apart-one with
the compensator's flicker mitigation turned off and the other
with it on.
April 2022 Show Issue
The flicker values previously had been increasing
throughout the day correlating with the PV output and
increased loading during the day. The analysis described in
IEEE 1453 can be used to determine compliance with the
flicker emission limits. This distribution grid falls under the
medium-voltage range, so the emission limits for Pst and Plt
are 0.9 and 0.7, respectively. Statistical analysis results are
shown in Table 2. Between these weeks, there was a ~37%
reduction in the Pst 95% probability value and a ~39% reduction
in the Plt 95% probability value, which brought the Pst
and Plt emission levels below the recommended limit.
Overall, the field data continued to validate the flicker mitigation
response shown in simulation and lab tests. The results
in both voltage regulation and flicker mitigation show how
effectively a power quality compensator at a large-scale PV
renewable generation site minimizes their negative effects on
distribution feeders and provides utilities with another tool to
enable more renewable penetration in their markets.
Conclusion
If the trends continue, DGPV will experience significant
growth in the coming years. The complexity of grid
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Parameter Set 1
Parameter Set 2
Parameter Set 3
246 81012
Frequency (Hz)
figure 6. Laboratory test results for flicker mitigation validation
- voltage feedback only.
figure 7. Field installation of 1MVA power quality compensator
(Source: Dominion Energy).
ieee power & energy magazine
103
Percent Flicker Mitigation (%)
IEEE PES T&D Conference & Exposition 2022

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