Distributed generation (DG), such as solar panels and wind turbines, is increasing around the world. While DG provides benefits, it also presents challenges for the existing electric grid which was designed for one-way power flow. To help manage these challenges, the document proposes installing AMSC's D-VAR VVO devices on distribution feeders. The D-VAR VVO uses power electronics to dynamically inject or absorb reactive power and regulate voltage across hundreds of customers, providing a more cost-effective solution than regulating voltage at each DG site individually. The D-VAR VVO aims to improve power quality issues caused by the intermittent nature of DG sources like solar and wind.

1. 1
Overview of Distributed
Generation
What is DG?
Distributed Generation (also called
Distributed Energy Resources, or DER) is
electricity generated within the distribution
grid, i.e., close to or directly at the
consumer level. It is energy produced and
used in contrast to the typical system of
electricity generated in far-off central
station power plants, sent through
transmission lines, and finally through a
distribution system to the end users. Types
of DG include biomass, wind turbines and
solar (photovoltaic, PV) panels.
Nations around the world confirm policy
changes toward renewable energy targets
as high as 20% by 2030. DG specifically is
estimated to rise globally to 165 gigawatts
of power by 2023, with the predominate
increase coming from solar (PV). The
growth of DG is due to several factors,
including political movements towards
renewable energy, economic incentives,
and reliability and security concerns related
to the centralized model. DG’s continued
penetration revolves around the lowering
cost of pertinent technologies, e.g., solar
panels. This cost curve implies that DG
(particularly PV) will become utilized more
and more by consumers as technology
improves.
What Does DG Mean for the
Distribution Grid?
The power distribution grid was designed
to deliver consistent energy to loads in
industrial, residential and commercial areas
– a one-way street. However, energy
production within the distribution network,
rather than at a power plant, is a game
changer. For instance, photovoltaic (PV) and
wind energy generate inherently irregular
and unpredictable output; day-to-day
weather patterns and cloud pass vary
generation output wildly across even one
distribution area. Because a large
percentage of DG is from wind and PV, grid
operation in turn becomes laden with
voltage flicker, voltage swells, poor power
factor, harmonics and other power quality
issues for which established equipment
simply cannot respond quickly, effectively or
often enough.
Maintaining voltage within a desirable
bandwidth to consumers requires a
comprehensive equipment strategy. Largely,
they are devices that manipulate the two
elements of AC current; “real” power
(typically expressed as Watts or
Megawatts), which is the component that
actually does wok. Real power is realized
when voltage and current are in phase with
each other. Conversely, “reactive” power
(expressed in VARs or MVARs) manifests
when voltage and current are not in phase.
Reactive power is unable to provide actual
work, but by either injecting or absorbing
it, VARs are a potent and proven method of
regulating voltage. This is called VAR
compensation.
Distributed Generation Revolution:
Dynamic Solutions for Grid Adaptation
A white paper by AMSC
Executive Summary
The driving elements of the power grid are shifting due to
technological innovations. For instance, steady cost reductions of
solar panels, coupled with their increased efficiency, have turned
rooftop solar installation from a trend to a veritable energy staple.
Growing economic benefits are transforming former energy
consumers into energy generators. However, consumer-based
generation is not what the grid was built for.
Originally designed in the early 20th Century, the grid brought
electricity by means of load-distant generation, through long
transmission lines, and finally to end users via a distribution
network. The 21st Century introduction of energy generation within
the distribution grid itself, called Distributed Generation (DG) or
Distributed Energy Resources (DER), has required a system built for
one-way delivery to be a bi-directional one. This white paper will
explore these dynamic changes to the grid, leading to
considerations for the future of distributed generation, and provide
strategic solutions, including the application of dynamic volt/VAR
compensation units, as manufactured by AMSC, purposefully
designed for increasing DG grid adaptation.
As DG penetration continues to rise, managing reliability and power
quality have become defining issues for the utilities industry. Of
particular concern is the intermittent nature of wind and solar DG
output. Changes in sunlight strength due to cloud pass events, and
lags and bursts of wind vary voltage generation for some sites,
while other sites continue normal operation within the same
distribution area. Conventional equipment (capacitor banks, voltage
regulators) will be unable to compensate for increased DG
penetration that is already demanding a more responsive grid
infrastructure. As part of solar installations, smart inverters provide
some localized grid support functions; however, utilities do not
typically own them, leaving these devices outside of a utility-
coordinated, tactical control scheme.
AMSC’s innovative dynamic volt ampere reactive (VAR) technology
has been applied successfully transmission systems for the past 15
years. These systems manage voltage irregularities, mitigating
capacitor bank switches, thus extending grid equipment lifespans.
With the growing adoption of DG, utilities now need effective
solutions to upgrade distribution grid infrastructure in a way that
doesn’t impact service costs to customers. Appointing small,
utility-owned volt/VAR compensation devices directly to the low
voltage DG site (typically 120V to 480V) would be inefficient, costly
and difficult to maintain. Application of such technology on
distribution feeders, however, could be used to manage voltage
flicker, voltage swells and other power quality concerns for
neighborhoods, business parks, and communities with a single
installation.
®TM

2. 2
Historically, the compensation for
fluctuations caused by demand/supply
shifts or other events have been managed
by devices that either coarsely add or
remove VARs (capacitor banks), or voltage
regulators that step-adjust to keep voltage
within an acceptable range. Being
mechanical in nature, all of these methods
are relatively slow to act. Step voltage
regulators (VR) are suitable to compensate
load deviations of greater than 10 minutes
in duration, while switched caps are
suitable for compensating for daily load
fluctuations. In practice, VR and cap banks
typically operate no more than 30 and 4
times per day, respectively.
Even with such technological impairments,
capacitor banks and VRs have been highly
effective in the past. Utilities have been able
to predict large changes in loads due to
day/night cycles, making the slow operation
of these devices relatively unproblematic.
They are also inexpensive to install.
Nonetheless, the dynamic response
limitations of these power quality
management systems are incompatible with
minute-to-minute voltage fluctuations
caused by renewable energy generation. If
the infrastructure doesn’t adapt, the
chances of poor power quality are widened
and the equipment will wear at a rate much
faster than anticipated.
Smart Inverters Help,
But Aren’t Utility-Controlled
Placed at solar panels, smart inverters are a
component of every PV installation to
convert the DC current produced by
sunlight into grid-ready AC current. As
DG-related grid complications can be
reduced at the point of interconnection,
smart inverters possess software that
provides grid support functions locally,
including limiting power ramp rate and
fixing power factor for a single site.
Configuring these functions at installation
time can be a cost-effective tool for
utilities to leverage. However, they are not
typically owned by the utility but rather by
the PV-generating customer themselves,
which makes them difficult tools to
strategically utilize.
In terms of VAR capacity, smart inverters
have significant limitations. The ratings
vary from manufacturer to manufacturer,
as well as differing due to installation site
and control settings (the sizing and rating
of a smart inverter is dependent on the PV
panel being used). As they are not
utility-operated, this leaves a smart
inverter’s capabilities, however helpful, out
of the utility’s control scheme. Since the
utility understands the full-picture
demands of distribution network, i.e.,
where certain power quality concerns are
most pressing, it is imperative that they
have dynamic equipment that they not
only own and control, but is also flexible
enough to respond to the unique power
quality issues of DG.
Utility-owned, Secondary Power
Electronics Are Uneconomical at Scale
In order to have optimal control, it may
seem prudent to apply utility-owned volt/
VAR compensation devices right at the DG
site on the secondary circuits. This would
manage instability before it affects the grid,
and give utilities administrative control as
well. However, installing so many units
(potentially as many sites as there are
consumers, in the case of rooftop solar) is
unrealistic in scale, time and cost.
Additionally, having so many units would
entail heavy maintenance; the more devices
within the network, the greater the
probability of failure due to malfunction or
environmental damage, resulting in
increased maintenance costs.
A highly effective solution at scale would be
powerful and flexible enough to control
voltage and power factor from multiple,
diverse sources, rather than for each DG
installation. This optimal device would be
installable upstream from DG sources on
15kV-class feeders, the most widely utilized
feeders in distribution system. This location
is ideal because it would act upon the
principal DG sites that cause power quality
concerns along the distribution grid, e.g.,
small industry, residential, agricultural and
offices, while requiring the least amount of
installations.
The Ideal,
Utility-Controlled Solution
D-VAR VVO
AMSC’s dynamic volt ampere reactive
technology solution, called D-VAR, has
effectively been used to manage voltage
profiles and power factor in wind farms, in
solar plants, and utility grids globally. Using
D-VAR systems, utility scale renewable
generation has been able to meet POI
voltage/PF regulating requirements, assist in
high and low voltage ride-through
capabilities, solve harmonic problems, and
improve power quality related grid
interconnection. Additionally, grid planners
have benefited from D-VAR’s dynamic
voltage regulation capability system and
advanced controls to reduce voltage
stability problems and optimize T&D
networks.
In response to increasing distribution grid
complexity, AMSC offers a specialized
edition of its D-VAR line called “D-VAR
VVO.” D-VAR VVO possesses the patented
volt/VAR compensating capabilities of its
parent technology such as moderating
step-voltage changes smoothly and rapidly,
Fig. 1 The D-VAR VVO installed in an above ground distribution feeder.

3. 3
and mitigating the stress on current
infrastructure. Whereas capacitor banks are
binary, and only able to add or remove fixed
VAR quantities, AMSC’s dynamic Volt/VAR
compensation technology gives D-VAR VVO
the ability to add or absorb VARs in an
adjustable, “dial-like” fashion.
D-VAR VVO is a unique, purpose-built
device that is designed to integrate
effortlessly into the distribution system with
the appropriate capabilities, the right size,
and at the optimal location for installation.
Rather than attempting to manage DG
interconnection at numerous sites with a
device at each, D-VAR VVO is installed on
15kV-class feeders to regulate voltage for a
whole region of the distribution circuit, i.e.,
the power quality for hundreds of
customers can be managed with each
installation. This means that there are less
devices needed to optimize the distribution
grid, minimizing cost while providing
precise voltage and power factor control.
Due to an innovative design with no
moving parts (e.g., no fans or pumps,
naturally cooled), D-VAR VVO requires no
routine maintenance and operates without
any perceptible acoustic noise. It also needs
no outside communication or controls to
perform its dynamic functionality, unless
desired as part of a utility’s control strategy.
AMSC’s strategic innovations sum up to a
cost-effective, practical solution to the
inevitable impediments of DG.
How D-VAR VVO Works
D-VAR VVO is a dynamic reactive power
compensator based on power electronics
technology. The D-VAR VVO manages
variability caused by DG/DER and other
threats to distribution voltage control by
injecting or by absorbing VARs as needed
with sub-cycle response time (compared to
60 seconds of typical VR and switched
caps), with limitless daily operations
(compared to <30 for VR and <4 for
switched caps). Because the power
electronics operate continuously, there are
no time intervals between volt/VAR
compensation tasks (compared to 10
minutes typical for switched caps), which is
ideal for the increasingly dynamic
distribution grid.
D-VAR VVO is a shunt device, making
installation directly on H-pole 15kV-class
feeders seamless. With this arrangement, it
adds no series impedance as voltage
regulators do, and minimizes BoS costs (i.e.,
no transformers, substations, fences, etc.)
Since 15kV feeders are an optimal
installation location where power quality
can be managed for hundreds of DG sites
simultaneously, D-VAR VVO is purposely
designed with 15kV standards in mind,
including protection gear.
While 15kV feeder application has clear
economical advantage, the varied DG
engagements occurring along many feeder
miles necessitates a customizable device;
on one lateral of the distribution grid, there
may be thirty rooftop solar DG, and at
another there may be only ten. Being a
“one-stop” DG solution, D-VAR VVO has
the flexibility to be installed in either single
phase or three phase formats. These
systems can compensate at the sub-cycle in
the range of 333kVAR, +/-500kVARs up to
+/-2MVARs, respectively, at a single
location.
Events triggering voltage flicker, voltage
swells, harmonic delinquencies and poor
power factor can be autonomously
stabilized through D-VAR VVO’s dynamic
control modes. D-VAR VVO can be
configured to operate in whichever mode
best suits the application (volt/VAR, grid PF,
or grid VAR), and also allows for scheduled
sequencing between modes. While no
external control is required, D-VAR VVO
provides utilities with secure access to its
control functions. This means it can be a
standalone, autonomous unit or can be
installed within a fleet of devices operating
towards a centralized control scheme.
D-VAR VVO incorporates AMSC’s proven
secure DnP3.0 network interface, which
can be readily configured to communicate
via preferred SCADA, DMS, and
distribution automation protocols.
DG
(PV)
DG
(PV)
DG
(PV)
D-VAR
VVO
Step VR
15kV Feeder
Substation
Loads
(customers)
Loads
(customers)
D-VAR VVO Switched caps
Partly Cloudy Days:
“Megawatts a
Minute”
Corrects for load
changes (time)
Daily operations
limit (type)
Reverse power
conditions
> 10 mins. 3-4 cycles
No limit
Robust
> 60 minutes
< 4
Can’t reduce
voltage
< 30
“Sensitive”
Fig. 2 The performance capability of the power-electronics based D-VAR VVO.

4. 4
Summary
Century-old techniques of managing utility
load – in one direction – are unfit for the
new age of distributed generation. The
distribution system requires new
innovations that are not only cost-effective
and dynamic to adapt it to the ever-
increasing penetration of DG, but also
utility-controlled towards the greatest
efficacy. Employing volt/VAR compensation
equipment on-site could reduce voltage
variations; however, this would require
numerous (and growing) devices, which in
turn would escalate installation,
maintenance and operating costs. The best
solution would have the flexibility and
power to serve expansively – with one to a
few installations required in a feeder. At the
seamless meeting of utility industry needs
and responsive solutions, AMSC’s D-VAR
VVO provides essential stability to the
increasingly dynamic distribution grid,
offering voltage and power factor control
for DG outputs at the ideal location on
15kV feeders.
D-VAR VVO Advantages for DG Grid Adaptation Include:
• DG & DER voltage instability concerns
are mitigated
• Ability to manage voltage violations
from multiple, diverse DG sources
• Shunt device, easily integrated,
optimal location on 15kV feeders
• Solves resonance issues associated
with cap banks
• No routine maintenance
• Unique, dynamic device, acting
in milliseconds
About AMSC
AMSC (NASDAQ: AMSC) generates the ideas, technologies and solutions that
meet the world’s demand for smarter, cleaner … better energy. Through its
Windtec Solutions, AMSC enables manufacturers to launch best-in-class wind
turbines quickly, effectively and profitably. Through its Gridtec Solutions, AMSC
provides the engineering planning services and advanced grid systems that
optimize network reliability, efficiency and performance. The company’s solutions
are now powering gigawatts of renewable energy globally and enhancing the
performance and reliability of power networks in more than a dozen countries.
Founded in 1987, AMSC is headquartered near Boston, Massachusetts with
operations in Asia, Australia, Europe and North America.
www.amsc.com
© 2017 AMSC. AMSC, GRIDTEC, GRIDTEC SOLUTIONS,
D-VAR, D-VAR VVO and SMARTER, CLEANER… BETTER
ENERGY are trademarks or registered trademarks of
American Superconductor Corporation or its subsidiaries.
DVARVVO_WP_0117
®