IEEE PES T&D Conference & Exposition 2022 - 97

different time scales: long-term following the day and night
cycle; seconds and minutes with effects such as clouding;
and in milliseconds due to slow voltage correction loops in
the DGPV plant controls. The combination of the different
effects on voltage at these different time scales may cause
these slower regulator technologies to experience many
switching cycles throughout the day, leading to early wearout,
if more appropriate control action is not taken.
Even with advanced controls to help prevent early wearout,
these technologies cannot mitigate all the issues that
accompany the more rapid voltage fluctuations, and these
issues will only compound as more photovoltaic (PV) or
similar intermittent generation is introduced to the grid in
the coming years. The United States solar industry alone
has seen an annual 42% increase in installed solar capacity
since 2011 and the inception of the SunShot Initiative by the
U.S. Department of Energy. Of this capacity, nearly 50% to
60% falls under the DGPV classification, meaning that more
of the slower regulator technologies at the distribution level
could be facing increased switching cycles and early wearout
while voltage fluctuation issues go unaddressed if faster
voltage regulation technology is not implemented.
Another factor is the location of typical DGPV sites.
These sites in rural areas may operate into higher impedance
lines leading to wide voltage variation and fluctuation with
generation. Network contingency conditions can also cause
greater impedance variations seen by these sites, requiring
variability in compensation for harmonics and unbalanced
loads. Also, reducing traditional generation results in the
operation of DGPV in higher impedance networks in both
typical distribution grids and micro-grids, potentially causing
higher rapid waveform changes when trying to optimize
the energy capture. Thus, the growth over the past decade has
consequently been driving the need for dynamic correction
capabilities provided by power electronics technologies such
as the static synchronous compensator (STATCOM) at distribution
level voltages, also known as a D-STATCOM. However,
many of these devices are limited in the power quality
issues that they can support, focusing primarily on fast voltage
regulation. In addition, these power electronics devices
compound the harmonics issues on the grid if not addressed.
The next step in technology and controls is providing a
solution that covers multiple power quality issues to eliminate
the need for the operator to specify and coordinate
varying power quality devices. This article describes an
advanced power quality compensator to provide fast-acting
voltage support,
flicker mitigation, harmonics mitigation,
current imbalance support, and power factor support with
additional benefits such as frequency regulation and peakshaving
when a real power energy storage element is added.
An introduction to this power quality compensator and its
design goals, control verification process, and field validation
when installed at a PV site are discussed in this article.
First, a few of the major power quality issues and their relaApril
2022 Show Issue
tion to DGPV are provided below to gain an appreciation of
the complex issues that the grid is facing.
Power Quality Compensator
Capabilities
Voltage Regulation
Voltage regulation techniques and technologies take many
forms depending on application-specific factors such as the
type of voltage event, the duration of the event, the fault isolation
strategy, and the robustness of the load to voltage perturbations
or excursions. For reference, a survey of different
voltage regulation technologies can be seen in Table 1. Classical
voltage regulation relies mostly on the ability to inject or
absorb reactive power or change the taps of regulating transformers
in the case of slower, steady-state voltage regulation.
A caveat in sizing these regulation devices is understanding
the feeder and impedance characteristics of the grid, local to
the loads that require voltage regulation. In many cases, it is
infeasible to support voltage sags with a shunt reactive power
device alone, and a series reactor or real power support will
be needed to boost the voltage enough to avoid interrupting
service to critical loads. Also, for long distribution lines with
a low X/R ratio, reactive power will be less effective on voltage
regulation, presenting the need for real power to boost
the voltage. In summary, understanding the application and
different types of voltage events is necessary when specifying
the best voltage regulation device.
IEEE 1159 classifies voltage events based on voltage magnitude
and typical duration. Voltage transients are defined as
high-magnitude (between 0-8 per unit) impulsive or oscillatory
events that will typically not exceed 8ms in duration. In
this range, many voltage regulation technologies will not be
able to react, and in cases such as a passive reactor or capacitor
bank, an oscillatory transient may induce a resonance
that amplifies the event. The only way to fully protect a load
from this type of event would be using a double-conversion
full voltage outage solution.
The next type of voltage event is a short-duration rootmean
square (RMS) variation, which is classified based on
the following: interruptions below 0.1 per unit (pu), sags
between 0.1-0.9pu, and swells above 1.1pu. The duration of
these events is defined as instantaneous between 8ms and
0.5s (0.5-30 cycles), momentary between 0.5 and 3s, and
temporary between 3s and 1m. If a distribution grid sees
excessive short-duration variations, a fast-acting voltage
regulation device may be used to eliminate some or all the
events, depending on the severity.
The voltage regulation device used in a particular situation
is highly dependent on the criticality of the loads on
the grid, other generation sources, and contingencies. For
example, if a distribution system depends on a high amount
of DGPV for generation, a severe voltage sag longer than
~1.25s may cause solar inverters to exceed the must-trip
ieee power & energy magazine
97
IEEE PES T&D Conference & Exposition 2022

Table of Contents for the Digital Edition of IEEE PES T&D Conference & Exposition 2022
