Describes a future in which the transmission grid can be controlled to optimize the use of cost-effective, clean generation resources while providing high-quality, reliable power. Summarizes the research that the Advanced Research Projects Agency - Energy (ARPA-E) is undertaking into hardware and software technologies that could significantly change the ability to control the flow of electricity in the power grid. This analysis is intended to describe potential benefits of a flexible transmission system achieved through power flow control technologies. Specifically, it categorizes the benefits of power flow control technologies and defines the impact of technologies used for power flow control. It also makes recommendations for further studies and analyses on power flow control. Written by ARPA-E interns Lotte Schlegel and Chris Babcock under the guidance of Josh Gould.

1.
Advanced
Research
Projects
Agency
for
Energy,
U.S.
Department
of
Energy
Benefits
of
Power
Flow
Control
Hardware
and
Software
Technologies
Lotte
Schlegel,
Chris
Babcock
and
Josh
Gould
9/27/2013

2. Contents
Purpose
and
Scope
......................................................................................................................................
3
Characteristics,
Capabilities
and
Technologies
of
a
Flexible
Grid
................................................................
3
Power
Flow
Control
Technology
Defined
................................................................................................
4
Hardware
.............................................................................................................................................
5
High
Voltage
Direct
Current
...............................................................................................................
5
HVAC
Power
Transmission
Controllers
(PTC)
.....................................................................................
7
Software
.............................................................................................................................................
9
Topology
Control
Algorithms
(TCAs)
..................................................................................................
9
Value
Analysis
of
Power
Flow
Control
.......................................................................................................
11
Identification
of
Value
Propositions
......................................................................................................
12
Asset
Management
............................................................................................................................
12
Reliability
and
Security
.......................................................................................................................
13
Congestion
Relief
...............................................................................................................................
14
Integration
of
renewable
energy
.....................................................................................................
14
Economic
Efficiency
.........................................................................................................................
15
Summary
of
Power
Flow
Control
Technology
Value
..............................................................................
18
Stakeholders
in
the
Transmission
Grid
Influence
Technology
Investment
Decisions
............................
18
Conclusion/Next
steps
...............................................................................................................................
21
References
.................................................................................................................................................
24
2

3. Purpose
and
Scope
Electricity
is
dynamic
–
supply
must
meet
demand
that
changes
by
the
second
in
the
electric
grid.
While
electricity
markets
have
evolved
to
price
supply
dynamically
and
demand
response
systems
have
developed
to
manage
demand
on
a
dynamic
basis,
the
transmission
grid
is
inflexible.
When
the
flow
of
electrons
is
disrupted
by
a
storm,
an
accident,
or
congestion
choking
the
lines
like
cars
on
an
interstate,
it
affects
the
wallets
of
people
and
businesses.
The
electric
transmission
grid
costs
consumers
billions
in
congestion
costs,
is
difficult
and
expensive
to
upgrade,
and
does
not
respond
quickly
to
contingency
events
–
costing
$79
billion
annually
in
power
interruptions
(Hamachi
LaCommare,
2004).
Transmission
infrastructure
in
the
U.S.
is
aging
-­‐
as
of
2008,
70%
of
transmission
lines
and
transformers
are
25
years
or
older
and
60%
of
circuit
breakers
are
30
years
or
older
(DOE,
2008).
The
electric
grid
of
the
future
will
need
to
be
sufficiently
flexible,
responsive,
and
reliable
to
support
variable
generation
resources,
reduce
areas
of
transmission
congestion,
and
respond
quickly
to
system
disruptions
due
to
severe
weather
events.
The
impending
upgrades
to
infrastructure
present
an
opportunity
to
include
technologies
to
improve
resiliency
of
the
grid.
Increasing
the
flexibility
of
the
electric
transmission
grid
can
be
the
cornerstone
to
addressing
all
of
these
challenges.
ARPA-­‐E’s
Green
Electricity
Network
Integration
“GENI”
program
envisions
a
future
in
which
the
transmission
grid
can
be
controlled
to
optimize
the
use
of
cost-­‐effective,
clean
generation
resources
while
providing
high-­‐quality,
reliable
power1.
To
that
end,
ARPA-­‐E
is
funding
research
into
transformative
hardware
and
software
technologies
that
could
significantly
change
the
ability
to
control
the
flow
of
electricity
in
the
power
grid.
This
analysis
is
intended
to
add
to
the
conversation
about
the
benefits
of
a
flexible
transmission
system
achieved
through
power
flow
control
technologies.
Specifically,
it
will
describe
and
categorize
the
benefits
of
power
flow
control
technologies
and
define
the
impact
of
technologies
used
for
power
flow
control.
It
will
also
make
recommendations
for
further
studies
and
analyses
on
power
flow
control.
Characteristics,
Capabilities
and
Technologies
of
a
Flexible
Grid
Historically,
the
electric
grid
was
designed
to
be
a
passive,
one-­‐directional
system.
To
improve
the
grid’s
reliability
and
turn
intermittent
power
sources
into
major
contributors
in
the
U.S.
energy
mix,
the
grid
needs
to
be
designed
and
operated
to
be
smarter
and
more
flexible.
Power
flow
control
is
one
way
to
increase
the
flexibility
and
resiliency
of
the
electric
grid.
Power
flow
is
determined
by
the
impedance
of
a
transmission
line
and
the
difference
in
voltage
at
each
end
(M.I.T.,
2011)2.
Power
flow
control
is
the
1
More
at
http://arpa-­‐e.energy.gov/?q=arpa-­‐e-­‐programs/geni
From
MIT’s
Future
of
the
Electric
Grid.
“Two
factors
determine
power
flow:
the
impedance
of
a
line
and
the
difference
in
the
instantaneous
voltages
at
its
two
ends.
Impedance
is
the
combination
of
resistance
and
reactance.
Resistance
accounts
for
energy
that
is
lost
as
heat
in
the
line.
It
is
analogous
to
the
physical
resistance
exerted
by
water
on
a
swimmer
or
wind
on
a
cyclist.
Energy
lost
in
this
way
can
never
be
recovered.
Reactance
accounts
for
energy
associated
with
the
electric
and
magnetic
fields
around
the
line.
This
energy
is
analogous
to
2
3

4. ability
to
change
the
way
that
power
flows
through
the
transmission
grid
using
hardware
and
software
to
maximize
system
value.
These
technologies
can
change
the
effective
impedance
of
the
network
or
the
sending
and
receiving
voltages
to
influence
the
path
of
electrons
flowing
through
the
transmission
grid.
This
enables
the
ability
to
hold
power
on
a
transmission
line
at
a
certain
level
or
direction.
Electrons
follow
the
path
of
least
resistance
(or
lowest
impedance),
and
the
result
of
changing
the
pathways
of
the
grid
is
to
change
the
way
that
power
flows
through
the
transmission
system.
Specifically,
power
flow
control
can
be
used
to
remove
congestion,
respond
to
contingency
events
(e.g.
loss
of
a
generator
or
transmission
line),
and
mitigate
power
quality
issues.
Power
flow
control
includes
the
faculties
to
control
the
voltage
or
impedance
on
given
major
transmission
lines,
switch
lines
on
and
off,
direct
power
from
one
line
to
another
to
increase
the
capacity
of
a
transmission
route,
provide
voltage
support,
transport
power
efficiently
over
long
distances,
and
quickly
reverse
the
direction
of
power
flow
from
one
area
to
another
in
response
to
contingencies.
A
system
planner
can
optimize
power
flow
on
a
system
by
choosing
among
technologies
to
enable
each
of
these
capabilities
as
appropriate.
In
order
to
fully
integrate
power
flow
control
at
the
system
level,
information
systems,
hardware
technology,
and
human
operators
at
ISOs/RTOs,
generators,
and
transmission
and
distribution
companies
coordinate
to
match
system
supply
and
demand
at
every
moment.
For
instance,
information
(such
as
forecasting
of
weather,
supply
and
demand),
sensors,
communication
devices,
and
control
technology
work
together
to
enable
physical
changes
to
the
transmission
grid.
As
power
flow
control
hardware
technologies
are
added
to
the
system,
coordinated
control
of
the
transmission
grid
will
maximize
the
efficacy
of
power
flow
control
and
ensure
reliability
across
the
system.
Changes
are
likely
required
to
optimize
the
coordination
of
the
grid
with
the
addition
of
power
flow
control
technologies
-­‐
for
instance,
as
variables
and
options
are
added
to
the
system,
either
a
central
operator
with
sufficient
computational
power
to
respond
to
dynamic
grid
conditions
or
coordinated
distributed
control
will
be
necessary
to
ensure
system
optimization.
Power
flow
control
can
increase
reliability
and
resiliency,
optimize
transmission
asset
efficiency
and
help
prioritize
new
transmission
construction
by
increasing
the
capacity
of
the
transmission
grid,
reduce
cost
to
electric
consumers,
facilitate
grid-­‐interconnection
of
generation,
storage,
demand
response,
and
detect
and
minimize
the
impact
of
unforeseen
disruption
events
such
as
extreme
weather.
The
following
sections
will
describe
the
technologies
that
enable
power
flow
control
and
the
value
that
power
flow
control
capabilities
afford
to
different
stakeholders
in
the
electric
grid.
Power
Flow
Control
Technology
Defined
Both
hardware
and
software
technologies
have
power
flow
control
applications.
This
analysis
will
focus
on
two
types
of
hardware
technologies
–
High
Voltage
Direct
Current
(HVDC)
transmission
cables
and
the
potential
energy
stored
when
riding
a
bicycle
up
a
hill.
It
is
recovered
(in
the
ideal
case)
when
going
down
the
other
side.
In
an
AC
line
in
the
U.S.,
this
energy
is
stored
and
recovered
120
times
per
second,
and
thus
is
quite
different
from
the
behavior
of
energy
stored
in
devices
such
as
batteries.
The
resistance
of
a
line
is
determined
by
the
material
properties,
length,
and
cross-­‐section
of
the
conductor,
while
reactance
is
determined
by
geometric
properties
(the
position
of
conductors
relative
to
each
other
and
ground).
In
practical
transmission
lines,
resistance
is
small
compared
to
reactance,
and
thus
reactance
has
more
influence
on
power
flow
than
resistance.”
4

5. substation
equipment;
and
High
Voltage
Alternating
Current
(HVAC)
power
transmission
controllers
that
use
power
electronics
to
augment
the
existing
AC
grid.
In
addition,
the
capabilities
enabled
by
software
control
algorithms
such
as
topology
control
are
discussed.
Hardware
Hardware
can
efficiently
direct
the
flow
of
power
on
the
grid,
help
stem
energy
losses,
and
enable
the
grid
to
be
more
responsive
and
resilient.
Advances
in
materials
and
engineering
are
decreasing
the
costs
of
power
flow
hardware;
many
of
the
concepts
of
which
have
been
around
for
a
long
time.
The
descriptions
below
include
power
flow
control
technologies
that
already
exist
and
are
in
wide
spread
use
in
the
grid
today,
as
well
as
emerging
technologies
not
yet
in
use
that
show
tremendous
promise
for
power
flow
control
applications.
High
Voltage
Direct
Current
transmission
systems
are
composed
of
one
or
more
DC
transmission
lines
or
cables
between
a
converter
(combined
rectifier
and
inverter),
which
converts
AC
to
DC
or
vice
versa.
The
DC
lines/cables
in
concert
with
the
most
recent
voltage
source
converter
(VSC)
technology
enable
rapid
control
of
the
direction
of
power
flow.
Both
voltage
and
current
source
converters
can
invert
DC
to
a
matching
AC
frequency
of
an
interconnected
AC
grid,
which
affords
HVDC
the
ability
to
connect
two
asynchronous
AC
systems.
DC
poses
fewer
technical
challenges
compared
to
AC
because
it
is
not
necessary
to
match
frequency,
phase
or
voltage.
DC
can
be
configured
as
a
monopolar
(one
cable)
or
bipolar
(two
cable)
system
which
offers
cost
savings
over
tripolar
AC
designs
which
require
one
cable
for
each
of
the
three
phases.
Because
of
this
and
the
lower
line
losses
(30-­‐50%
lower
as
compared
to
AC),
HVDC
transmission
lines
are
the
least
expensive
option
for
transmitting
power
over
long
distances
(Reed,
2012).
HVDC
transformers
have
been
more
expensive
relative
to
HVAC.
The
distance
at
which
a
given
HVDC
line
becomes
more
cost
effective
than
HVAC
at
a
given
voltage
is
the
difference
between
line
and
terminal
costs
including
the
difference
between
losses
(see
Figure
1).
Also,
when
connected
with
an
AC
grid,
HVDC
can
mitigate
power
factor
issues
(current
lagging/leading
voltage)
by
providing
reactive
power
support,
and
can
provide
black
start
capabilities3
with
VSCs.
HVDC
transmission
systems
are
used
to
transport
power
over
long
distances
and
sub-­‐sea.
HVDC
lines
with
VSCs
allow
for
bi-­‐directional
control
of
power
flow
and
can
be
directly
scheduled
and
dispatched.
Bi-­‐directionality
allows
for
the
export
of
energy
from
control
area
A
to
control
area
B
under
certain
conditions,
and
re-­‐dispatch
for
import
of
energy
from
area
B
to
area
A
in
other
scenarios.
One
example
of
bi-­‐directional
flow
is
the
HVDC
cross
channel
2,000
MW
link
that
imports
electricity
to
Britain
from
France
during
much
of
the
year,
but
exports
power
to
France
during
the
summer
when
demand
is
high
or
to
meet
load
during
scheduled
outages.
The
Cross
Sound
Cable
between
Connecticut
and
Long
Island
is
also
bi-­‐directional,
although
power
flows
from
Connecticut
to
Long
Island
for
most
hours
of
the
year.
3
Black
start
is
the
process
of
restoring
power
to
a
power
plant,
normally
without
relying
on
the
power
of
the
transmission
grid.
Typically
in
the
case
of
a
wider
grid
outage,
black
start
is
provided
in
a
sequence:
a
portable
generator
is
used
to
start
one
power
plant,
the
proximal
transmission
lines
are
energized
and
the
power
used
to
start
the
next
base
load
generator,
and
so
on.
Voltage
Source
Converters
can
be
used
for
black
start
as
they
can
synthesize
a
balanced
set
of
three
phase
voltages.
5

6.
Fig.
1.
Breakeven
distance
for
HVDC
transmission
lines
HVDC
becomes
cost
competitive
with
HVAC
over
a
distance
at
which
line
losses
at
a
given
voltage
are
lower
than
a
comparable
HVAC
line.
Source:
Pike
Research,
2012
HVDC
technology
has
gained
popularity
since
the
mid-­‐20th
century.
Historically,
the
limitations
to
its
practical
use
have
been
the
high
cost
of
the
power
electronics
required
for
the
converter.
Recent
technical
breakthroughs
have
reduced
the
cost
of
power
electronics
and
increased
their
application.
HVDC
is
now
being
deployed
globally,
with
dozens
of
projects
in
the
global
pipeline,
and
is
of
particular
importance
to
integrating
distant,
renewable
energy
generators
such
as
offshore
wind
farms.
When
considering
new
transmission
corridors,
HVDC
is
more
favorable
to
HVAC
because
of
the
smaller
footprint
of
the
transmission
towers.
HVDC
proponents
envision
a
future
in
which
DC
cables
are
embedded
within
the
existing
AC
grid
and
multi-­‐terminal
HVDC
allows
for
a
superimposed
HVDC
network
that
will
help
to
integrate
remote
resources,
improve
system
stability
and
reliability
via
AC-­‐DC
interties,
and
increase
control
of
power
flows
through
the
system.
HVDC
technologies
are
being
developed
by
numerous
vendors,
including
General
Electric
with
funding
from
the
ARPA-­‐E
GENI
program.
GE
Global
Research
is
developing
two
ARPA-­‐E
funded
projects
to
improve
HVDC
technology
–
multi-­‐terminal
HVDC
and
improved
cable
insulation.
The
multi-­‐terminal
HVDC
Networks
with
High-­‐Voltage
High-­‐
Frequency
Electronics
project
is
developing
multi-­‐terminal
HVDC-­‐
compatible
converters
to
improve
the
ability
to
network
HVDC
and
integrate
renewable
energy
into
the
grid.
Nanoclay
Reinforced
Ethylene-­‐Propylene-­‐Rubber
for
Low-­‐Cost
HVDC
Cabling
project
is
developing
low-­‐cost
insulation
for
HVDC
transmission
cables.
Cables
will
be
less
expensive
and
suppress
excess
charge
accumulation,
which
will
protect
the
insulation.
6

7. HVAC
Power
Transmission
Controllers
(PTC)
can
control
impedance,
voltage
and
phase
and
hold
power
at
a
desired
level
and
direction
of
flow.
PTC
devices
use
a
combination
of
solid
state
power
electronics
and
other
static
equipment
to
modulate
the
state
of
a
given
AC
transmission
line
by
injecting
and
removing
voltage
and
impedance.
These
coordinated
actions
result
in
controllable
voltage/current
phase
shift
to
manage
real
and
reactive
power
flows,
controllable
line
impedance
to
increase
or
decrease
current,
and
the
ability
to
balance
the
current
phase
between
the
three
phases
of
an
AC
transmission
system.
Historically,
these
capabilities
were
accomplished
by
Flexible
Alternating
Current
Transmission
Systems
(FACTS),
which
employed
similar
power
electronic
devices
in
substations
and
were
typically
large
and
capital
intensive.
Today,
advances
in
technology
are
decreasing
the
cost
and
footprint,
and
increasing
the
reliability
and
operability
of
these
devices,
making
HVAC
PTC
viable
solutions
for
power
flow
control
applications.
Such
devices
are
being
developed
by
several
ARPA-­‐E
GENI
teams,
including
Smart
Wire
Grid,
Varentec,
Oak
Ridge
National
Laboratory,
and
Michigan
State
University.
Phase
Shifting
Transformers
Phase
shifting
transformers
change
the
voltage
phase
angle
between
primary
and
secondary
windings,
changing
the
input
and
output
voltages
of
a
line
and
thereby
controlling
the
active
power
that
can
flow
in
the
line.
Effectively,
they
inject
a
voltage
in
series
with
the
line.
This
enables
control
of
power
flow
between
two
power
systems,
balances
loading,
and
improves
system
stability.
Dynamic
Power
Flow
Controller
Varentec
is
developing
low
cost
transmission
controllers
to
dynamically
control
voltage
and
power
flow
with
ARPA-­‐E
funding.
The
technology
would
enable
early
detection
and
fail-­‐safe
protection
of
the
transmission
grid
to
maintain
its
operating
state.
Magnetic
Amplifier
for
Power
Flow
Control
Oak
Ridge
National
Laboratory
is
developing
an
electromagnet-­‐based
amplifier-­‐like
device
that
will
allow
for
complete
control
over
the
flow
of
power.
The
prototype
device
is
a
low
cost
iron-­‐based
magnetic
amplifier.
Distributed
Series
Reactor
The
Distributed
Series
Reactor
(DSR)
is
a
technology
being
developed
by
Smart
Wire
Grid,
a
startup
based
in
Oakland,
California.
DSRs
are
small,
single-­‐turn
transformers
that
inject
inductance
onto
a
transmission
line.
The
level
of
inductance
is
tunable
to
alter
the
overall
line
impedance
and
thus
the
flow
of
current.
DSRs
are
distributed
along
transmission
lines,
in
all
3
phases,
and
can
communicate
with
each
other
to
form
a
variable
impedance
system.
They
can
also
operate
autonomously
to
alter
flows
at
a
specific
point
on
the
line.
As
such,
the
technology
can
help
to
reduce
congestion
and
balance
power
flow
within
a
system.
7

8. Shunt
Compensators
Shunt
devices
are
used
to
control
transmission
voltage,
reduce
reactive
losses,
dampen
power
oscillations
and
are
connected
in
shunt
to
a
transmission
line.
A
Static
Synchronous
Compensator
(STATCOM)
is
a
VSC
usually
connected
to
the
grid
through
a
shunt
transformer.
STATCOMs
do
not
require
the
bulk
capacitors
and
inductors
that
are
used
in
the
thyristor-­‐based
Static
Var
Compensators
(SVCs)
which
are
still
in
widespread
use
today.
Instead,
the
STATCOM
generates
reactive
power
entirely
electronically
and
can
act
as
either
a
source
or
sink
of
reactive
power.
The
STATCOM
can
also
exchange
real
power
between
the
grid
and
an
energy
storage
device
connected
at
its
DC
terminals.
VSCs
based
on
Insulated-­‐gate
bipolar
transistor
(IGBT)
technology4
have
much
faster
switching
times
than
other
compensator
technologies,
which
makes
them
particularly
useful
for
dynamic
voltage
support
and
power
factor
correction.
A
STATCOM
does
not
affect
power
flow
on
a
transmission
line
directly.
However,
by
using
local
shunt
reactive
power
injection
to
change
the
voltage
profile
of
a
transmission
line
(e.g.
support
voltage
at
the
midpoint
of
a
long
line),
it
can
enable
a
line
to
be
loaded
more
heavily
(e.g.
to
thermal
limits)
without
exceeding
steady
state
stability
margins
or
voltage
drop
limits.
In
contracts,
a
power
flow
controller
is
connected
in
series
with
a
transmission
line
and
has
the
ability
to
force
a
change
in
power
flow
on
the
line,
essentially
by
introducing
a
controllable
voltage
in
series
with
the
line.
Series
Compensators
A
Static
Series
Synchronous
Compensator
(SSSC)
is
a
VSC
connected
in
series
with
a
transmission
line.
It
has
the
ability
to
raise,
lower,
or
even
reverse
the
power
flow
on
the
line
by
injecting
a
relatively
small
voltage
in
series.
For
a
wide
range
of
power
flow
control,
only
reactive
power
output
from
the
VSC
is
needed.
However,
additional
control
capabilities
such
as
independent
control
of
real
and
reactive
power
flow,
can
be
obtained
if
a
source/sink
of
real
power
is
connected
to
the
DC
terminals
of
the
VSC.
Currently,
there
are
no
examples
of
SSSC
installations
in
transmission
grids
except
those
installed
as
part
of
the
three
Unified
Power
Flow
Controller
demonstration
projects.
A
stand-­‐alone
SSSC
is
a
more
versatile
(and
potentially
lower-­‐cost)
power
flow
controller
than
a
Thyristor-­‐Controlled
Phase
Angle
Regulating
Transformer
with
a
similar
MVA
rating,
which
is
the
closest
comparable
device.
At
present,
back-­‐to-­‐back
HVDC
is
being
considered
in
some
places
to
solve
loop
flows
and
other
transmission
problems,
but
requires
two
converters
rated
for
full
transmitted
power.
In
most
cases
the
problem
could
be
solved
with
a
single
fractionally
rated
SSSC.
4
IGBT
technology
is
a
power
semiconductor
device
that
forms
an
electronic
switch.
They
are
high
efficiency,
fast
switching
and
can
handle
high
voltages
and
current
when
many
devices
are
stacked
in
parallel.
8

9. Thyristor
Controlled
Series
Capacitors
(TCSC)
are
a
family
of
equipment
that
provides
a
controllable
capacitance
(or
in
some
cases,
an
inductance)
connected
in
series
with
a
transmission
line
to
reduce
(or
increase)
the
total
reactance
of
the
line.
Unified
Power
Flow
Controllers
(UPFCs)
UPFCs
provide
the
functionality
of
both
shunt
and
series
compensators.
They
control
real
and
reactive
power
flow
and
provide
voltage
support
for
the
connecting
bus5.
Historically,
UPFCs
have
taken
up
significant
space,
been
very
expensive,
and
required
the
construction
of
large
transformers.
There
are
only
three
operational
UPFCs
in
the
world,
each
of
which
was
tailored
to
meet
a
particular
utility’s
problem.
However,
grid
operators
are
largely
uncomfortable
with
the
series
compensation
capabilities
of
UPFCs,
and
as
a
result
these
operating
modes
are
rarely
used,
leaving
the
UPFCs
to
operate
largely
as
a
STATCOM
(for
more,
see
Marcy
UPFC
case
study
in
this
document).
Moreover,
the
company
that
built
the
UPFCs
–
Westinghouse
–
was
acquired
by
Siemens,
which
no
longer
sells
or
supports
the
devices.
An
ARPA-­‐E
team
from
Michigan
State
University
is
building
a
transformer-­‐less
UPFC
which
addresses
these
issues
and
can
control
power
flows
from
intermittent
resources
including
wind
and
solar
resources.
Transformer-­‐Less
Unified
Power
Flow
Controller
Michigan
State
University
is
developing
a
power
flow
controller
to
improve
the
routing
of
electricity
from
renewable
sources
through
existing
power
lines.
The
UPFC
will
eliminate
the
need
for
a
transformer
and
construction
of
new
transmission
lines.
It
will
optimize
energy
transmission
and
h elp
reduce
transmission
congestion.
Software
Advancements
in
computing
and
data
communications
can
optimize
grid
operations,
match
power
delivery
to
real-­‐time
demand,
and
find
effective
ways
to
manage
sporadically
available
renewable
power
sources
and
grid-­‐level
power
storage.
Topology
Control
Algorithms
(TCAs)
are
a
network
solution
to
optimally
activate
(close)
and
deactivate
(open)
transmission
lines
to
decrease
the
cost
of
the
transmission
system.
This
is
based
on
the
counter-­‐intuitive,
but
demonstrated,
phenomenon
that
closing
a
congested
pathway
improves
the
overall
system
flow6.
TCAs
are
integrated
into
software
that
controls
the
grid’s
hardware
infrastructure,
5
Real
power
is
power
delivered
to
the
end
user
to
do
work
(measured
in
watts).
Reactive
power
is
current
energizing
the
system
components
(measured
in
volt-­‐amperes
reactive-­‐
VAR).
6
Closing
a
congested
pathway
can
open
the
electric
flow
at
the
system
level.
This
has
been
demonstrated
by
ISOs
and
researchers,
including
the
Brattle
Group,
Argonne
National
Labs,
and
a
team
from
Texas
A&M.
To
illustrate
this
concept
a
team
from
Texas
A&M
showed
that
when
a
50MW
line
was
dropped
in
a
3-­‐line,
3-­‐generator
system,
the
feasible
cost
to
serve
load
dropped.
This
concept
is
demonstrated
in
the
diagrams
below:
9

10. and
change
the
shape
of
the
grid
by
actuating
line
switching
hardware
or
by
controlling
the
HVAC
PTC
devices
listed
above.
The
net
effect
of
changing
the
shape
of
the
grid
is
to
change
the
way
that
power
flows
through
the
transmission
system.
TCAs
are
not
a
new
concept;
they
have
been
employed
by
operators
of
wireless
ad-­‐hoc
networks
for
radios
(since
1970’s)
and
computers
(since
1990’s)
by
optimizing
the
transmission
power
of
each
node
to
improve
signal
flow
in
the
network.
For
the
electric
power
industry,
recent
advances
such
as
phasor
measurement
units
(PMUs),
low-­‐latency
communication
systems,
and
the
reduced
cost
and
improved
speed
of
computer
processors
allow
for
TCAs
to
be
an
effective
solution
for
power
flow
in
the
transmission
grid.
TCAs
are
being
developed
through
the
ARPA-­‐E
GENI
program
by
Texas
A&M
and
Boston
University.
Automated
Grid
Disruption
Response
System
Texas
A&M
is
developing
a
Robust
Adaptive
Topology
Control
(RATC)
system
designed
to
detect,
classify,
and
respond
to
grid
disturbances
by
reconfiguring
the
grid
to
maintain
economically
efficient,
reliable
operations.
The
system
would
help
to
prevent
outages
and
minimize
the
time
it
takes
for
the
grid
to
respond
to
interruptions,
and
make
it
easier
to
integrate
renewable
resources
into
the
grid.
Transmission
Topology
Control
for
Infrastructure
Resilience
to
the
Integration
of
Renewable
Generation
Boston
University
is
developing
a
technology
that
helps
grid
operators
manage
power
flows
and
integrates
renewable
resources
by
optimizing
the
transmission
system.
The
system
would
have
the
capability
of
turning
power
lines
on
and
off
to
manage
transmission
congestion,
increase
use
of
renewable
resources,
and
improve
system
reliability.
The
fast
optimization
algorithms
would
enable
near
real-­‐time
change
in
the
grid.
10

11. Value
Analysis
of
Power
Flow
Control
Power
flow
control
benefits
the
entire
transmission
system
as
well
as
transmission
owners,
generators,
operators,
planners,
regulators,
and
consumers.
Transmission
benefits
can
be
numerous
and
diverse,
including:
•
•
•
•
•
•
•
•
Reduce
energy
transmission
losses
Mitigate
transmission
outages
Defer
and
prioritize
transmission
investments
Increase
transfer
capability
from
one
part
of
the
system
to
another
Reduce
cycling
of
base
load
generators
to
increase
asset
efficiency
Increase
wheeling
of
power
in
and
out
Reduce
loop
flows
Meet
public
policy
goals
Any
one
of
the
technologies
described
above
can
help
to
achieve
these
benefits.
However,
to
maximize
the
benefits
of
power
flow
control
and
to
maintain
system
reliability,
some
system
coordination
is
required
in
order
to
understand
the
system-­‐level
effect
of
the
installation
of
power
flow
control
technologies,
to
plan
for
future
asset
mix,
and
to
optimize
operations
of
the
physical
grid
and
electricity
markets.
Power
flow
control
is
achieved
when
software
technologies
in
concert
with
well-­‐placed
hardware
work
together
to
optimize
the
transmission
system.
Ultimately,
planners,
operators
and
regulators
may
need
to
consider
several
additional
factors
to
realize
the
full
potential
and
system
benefits
of
power
flow
control
technologies,
including:
•
•
•
Market/regulatory
structure
for
wide
area
control
–
to
make
sure
that
market
structure
and
technical
capabilities
are
aligned
to
properly
value
the
benefits
of
power
flow
control
technologies
Software
–
synchronous
access
to
cloud
resources
for
optimized
coordinated
control
Sensors
–
accurate,
real-­‐time,
dispersed
estimation
sensors
to
measure
and
communicate
the
conditions
of
the
electric
grid
in
real
time
and
ensure
This
analysis
does
not
consider
the
many
complementary
technologies
that
would
help
to
maximize
flexibility
and
control
including
PMUs,
advanced
metering
infrastructure
or
distribution-­‐level
technologies,
or
incentives
and
market
structures
that
could
enable
power
flow
control.
The
analysis
is
solely
focused
on
the
high-­‐voltage
transmission
technologies
and
software
applications
described
above.
One
can
think
of
the
value
of
power
flow
control
technologies
in
terms
of
the
total
costs
and
benefits
of
a
transmission
grid
with
power
flow
control
capabilities
as
compared
to
the
total
cost
and
benefits
of
the
system
without
these
capabilities.
However,
one
of
the
difficulties
in
quantifying
the
value
of
power
flow
control
capabilities
is
that
system
optimization
requires
that
there
be
short-­‐term
beneficiaries
of
a
change
in
power
flow,
and
corresponding
entities
that
might
see
a
drop
in
revenue
in
the
short-­‐term,
as
any
change
to
the
physical
constraints
of
the
electric
grid
can
affect
the
price
that
generators
or
transmission
owners
are
paid
for
electricity.
This
analysis
explores
five
distinct
value
streams
of
power
11

12. flow
control,
defines
the
associated
benefits
and
costs,
and
identifies
the
stakeholders
and
how
they
might
be
affected
at
a
system
level.
Identification
of
Value
Propositions
Asset
Management
Transmission
infrastructure
in
the
United
States
is
built
to
meet
peak
demand,
which
leads
to
sub-­‐
optimal
utilization
outcomes
at
a
system
level
during
non-­‐peak
periods.
Reliability
standards
and
favorable
FERC-­‐established
rates
of
return
provide
incentives
for
transmission
investment.
At
the
same
time,
much
of
the
existing
transmission
infrastructure
is
reaching
the
end
of
its
useful
life,
and
new
transmission
is
difficult,
expensive,
time-­‐consuming,
and
highly
litigious
to
build.
Transmission
owners
are
also
faced
with
competing
calls
for
capital
to
meet
reliability
and
environmental
priorities.
Research
from
the
Edison
Electric
Institute
shows
that
its
shareholder-­‐owned
utility
members
increased
their
investment
in
transmission
infrastructure,
investing
$11.1
billion
in
2011
and
planning
to
spend
$54.6
billion
through
2015
(Edison
Electric
Institute).
Several
power
flow
control
technologies
could
increase
the
capacity
of
existing
transmission
lines
and
defer
new
investment
in
construction
or
help
prioritize
construction
of
new
lines
to
optimize
the
use
of
the
transmission
grid.
While
increasing
the
capacity
of
transmission
lines
would
produce
system-­‐level
benefits,
ultimately
some
transmission
owners
and
electricity
generators
would
see
lower
revenues
in
cases
where
they
currently
benefit
from
congestion.
HVDC
In
some
scenarios,
power
flow
control
technologies
could
decrease
transmission
losses
and
increase
transmission
utilization.
Most
notably,
HVDC
lines
have
lower
losses
in
transporting
power
over
long
distances,
and
technological
advances
in
insulation
could
increase
this
benefit
further.
For
instance,
GE
Global
Research
is
developing
a
nanoclay
reinforced
ethylene-­‐propylene-­‐rubber
for
low-­‐cost
HVDC
cabling
that
could
bring
down
the
cost
of
HVDC
cable
by
as
much
as
80%.
Such
a
decrease
in
the
cost
of
HVDC
would
lower
the
distance
at
which
HVDC
is
cost
competitive
with
HVAC,
and
increase
its
affordability
as
an
option
for
integration
into
the
AC
grid.
HVDC
requires
smaller
transmission
right
of
ways,
so
new
construction
or
reconductoring
of
transmission
lines
can
be
easier
to
achieve.
This
is
particularly
important
in
heavily
populated
areas,
which
often
suffer
from
transmission
congestion.
In
these
cases,
transmission
planners
may
consider
using
existing
transmission
right
of
ways
to
install
buried
HVDC
cable
to
increase
transmission
capacity
without
permitting
a
completely
new
transmission
pathway.
Power
Transmission
Controllers
and
Topology
Control
Algorithms
HVAC
PTCs
such
as
DSRs
and
STATCOMs
can
increase
the
capacity
of
AC
transmission
infrastructure
and
reduce
the
need
for
a
new
transmission
line,
to
optimize
the
existing
AC
transmission.
Because
repowering
existing
assets
could
be
less
costly,
a
transmission
owner
could
prioritize
capital
expenditures
and
deploy
resources
for
new
transmission
lines
in
parts
of
the
system
where
it
would
12

13. make
the
most
difference.
In
addition,
they
can
increase
the
flexibility
and
adaptability
for
grid
operators
to
use
existing
AC
lines.
Topology
control
allows
for
line
switching
to
optimize
economic
efficiency
and
minimize
congestion.
In
some
cases,
employing
topology
control
alone
would
increase
the
utilization
of
transmission
lines
and
defer
the
need
for
new
transmission
construction.
One
common
concern
about
topology
control
is
that
it
might
increase
circuit
breaker
operations
and
maintenance
expenses.
Under
a
scenario
with
topology
control,
circuits
will
be
switched
more
frequently,
but
in
non-­‐fault
conditions
with
much
less
current.
Circuit
breakers
have
a
robust
design
to
deal
with
fault
conditions
are
expected
to
operate
will
in
a
topology
control
case.
However,
equipment
manufacturers
will
need
to
validate
and
support
this
new
use
case.
Circuit
breakers
that
are
old
and
past
warranty
may
be
of
greater
concern
in
than
newer
devices.
While
it
is
thus
possible
that
line
switching
could
increase
the
need
for
maintenance
on
breakers
that
are
used
more
frequently
in
switching
than
static
scenarios,
the
system-­‐level
benefits
should
outweigh
the
costs.
Reliability
and
Security
Where
power
systems
are
designed
to
meet
one
or
two
contingency
extreme
events,
power
flow
control
capabilities
could
help
to
mitigate
the
impact
of
one
or
two
outages
by
providing
alternate
power
flow
paths
to
continue
to
serve
load.
The
economic
impact
of
the
infamous
northeastern
August
2003
blackout
was
estimated
to
be
$4
to
$10
billion
in
the
United
States,
highlighting
the
importance
of
the
electric
grid
in
today’s
economy
(U.S.-­‐Canada
Task
Force,
2004).
Reliability
is
top
of
mind
for
system
operators,
regulators,
policy
makers,
and
businesses
in
the
U.S.
today,
as
reflected
in
the
regional
implementation
of
North
American
Electric
Reliability
Corporation
(NERC)
standards.
Power
flow
control
technology
could
increase
the
flexibility
and
responsiveness
of
the
grid.
HVDC
HVDC
technology
provides
several
reliability
benefits.
Specifically,
a
DC
circuit
breaker
with
instantaneous
response
time
will
allow
for
quick
fault
detection
and
response,
which,
in
conjunction
with
other
power
flow
control
technologies,
can
prevent
a
system-­‐level
problem
and
re-­‐route
power
to
enable
continual,
uninterrupted
service.
Similarly,
directional
switching
of
power
flow
enables
routing
options
post-­‐contingency.
The
ability
to
reverse
power
flow
in
response
to
a
contingency
can
decrease
generation
capacity
requirements
for
ancillary
services.
In
the
case
of
an
HVDC
intertie
between
two
asynchronous
grids,
VSCs
can
provide
black
start
service
from
one
grid
to
another,
significantly
decreasing
response
time
without
the
need
for
reserve
installations
that
would
otherwise
be
idle
much
of
the
year.
Power
Transmission
Controllers
and
Topology
Control
Algorithms
DSRs,
STATCOMs,
and
TCAs
each
provide
reliability
benefits.
DSRs
can
control
potential
transmission
overload
and
bypass
congested
lines,
increasing
transmission
utilization,
decreasing
congestion,
and
thereby
increasing
dispatch
options.
The
built
in
device-­‐to-­‐device
communication
system
in
DSRs
13

14. enables
dynamic,
autonomous
response
and
eliminates
risks
associated
with
other
central-­‐control
communications
devices.
The
AC
regulation
function
of
STATCOMs
can
automatically
control
transmission
contingency
conditions
and
prevent
problems
or
decrease
recovery
time.
TCAs
will
optimize
transmission
line
switching
under
normal
and
contingency
conditions
–
bypassing
congested
lines
and
finding
the
optimal
path
to
serve
load.
In
order
to
quantify
the
specific
benefits
of
power
flow
control
technologies
on
a
particular
system,
it
would
be
necessary
to
model
the
grid
response
under
contingency
conditions
using
reliability
software,
and
then
again
with
power
flow
control
technologies
built
in
and
estimating
the
economic
value
of
the
reduction
in
load
loss
(Budhraja,
Mobasheri,
Ballance,
Dyer,
Silverstein,
&
Eto,
2009).
Congestion
Relief
Transmission
congestion
happens
whenever
preferable
or
low
cost
generation
is
unable
to
serve
electric
load
due
to
a
physical
limit
on
the
transmission
system.
Market
efficiency
is
based
on
optimal
economic
operation
of
the
grid
by
dispatching
the
lowest-­‐cost
generation.
Congestion
disrupts
this
process
and
leads
to
dispatch
of
higher
cost
generation
to
meet
demand
in
the
importing
location,
and
exerts
downward
pressure
on
prices
in
exporting
areas.
Reducing
congestion
on
the
transmission
grid
will
reduce
congestion
pricing
for
energy
and
ancillary
services
and
allow
for
economic
dispatch
of
generation
while
balancing
transmission
lines.
At
a
system
level,
the
cost
of
constructing
new
transmission
lines
or
adding
power
flow
control
technologies
must
be
weighed
against
the
benefits
of
doing
so.
Congestion
is
often
a
problem
in
or
around
densely
populated
areas,
where
permitting
new
transmission
lines
can
be
particularly
difficult.
In
these
cases,
there
may
be
a
clear
system-­‐level
benefit
to
power
flow
control
technologies.
Congestion
relief
brings
multiple
benefits
in
terms
of
integration
of
renewable
energy
and
economic
efficiency
of
energy
markets.
Integration
of
renewable
energy
Multiple
renewable
integration
studies
have
validated
the
substantial
system
level
and
societal
benefits
of
increased
renewable
energy
penetration.
Wind
and
solar
energy
generators
reduce
the
system
operating
costs
by
displacing
fuel
expenses
and
deferring
upgrades
to
existing
conventional
generators;
in
addition
to
lowering
generation
fleet
carbon
emissions.
In
the
Western
Wind
and
Solar
Interconnection
Study
(WWSIS),
it
was
found
that
by
tapping
the
large
solar
and
wind
resource
in
the
Western
Connection,
up
to
35%
of
the
required
energy
could
be
delivered
by
renewables
(GE
Energy,
2010).
This
results
in
a
40%
reduction
in
the
annual
system
OPEX.
In
the
Eastern
Wind
Integration
and
Transmission
Study
(EWITS),
a
10%
reduction
in
annual
system
OPEX
was
achieved
by
incorporating
30%
of
the
energy
requirement
from
wind
in
the
Eastern
Connection
(EnerNex
Corporation,
2011).
EWITS
also
calculated
an
18%
reduction
in
CO2
emissions.
The
challenge
to
incorporating
variable,
uncertain
renewable
energy
is
that
the
current
system
infrastructure
and
operational
practices
were
designed
for
dispatch-­‐able
and
predictable
generation
supplies.
However,
renewable
energy
generators,
such
as
wind
and
solar,
are
variable
and
uncertain
(non-­‐perfectly
predictable)
due
to
the
nature
of
wind
and
cloud
coverage.
This
variability
and
14

15. uncertainty
has
the
potential
to
exacerbate
transmission
congestion
as
the
penetration
of
renewable
generation
increases.
Conversely,
there
might
be
an
under
supply
of
energy
or
system
frequency
disruption
if
the
renewable
generators
slow
or
stop
production
(due
to
ramping).
To
mitigate
these
challenges,
system
operators
can
require
additional
reserve
capacity
to
supplement
renewables
and
come
online
quickly
to
stabilize
system
frequency
in
the
event
of
ramping
of
the
energy
resource.
Other
generators
must
perform
load
following
to
match
their
output
to
any
changes
in
the
energy
supply-­‐demand
balance.
Furthermore,
local
generators
are
called
upon
in
instances
when
congestion
prevents
renewable
energy
from
serving
the
load.
In
this
case,
current
practice
empowers
grid
operators
to
curtail
renewable
generators
if
their
supply
cannot
be
reliably
transmitted
due
to
congestion
elsewhere
in
the
system.
In
all
these
cases,
the
operation
of
reserve
generators
is
generally
higher
cost
than
the
renewable
generators.
Some
system
operators
have
begun
to
utilize
forecasts
of
renewable
energy
regions
to
aid
in
more
economic
reserve
scheduling
and
transmission
system
operation.
However,
the
accuracy
of
these
forecasts
at
present
is
marginally
better
than
assuming
persistence.
Poor
information
leads
to
inefficient
dispatching
and
un-­‐necessary
cycling
of
conventional
generators
which
is
a
less
efficient
operational
method
that
outputs
greater
emissions
and
more
wear
and
tear
on
the
asset.
These
additional
operational
requirements
of
renewables
are
manageable,
but
lessen
the
total
achievable
system
benefits
due
to
the
increased
demand
for
real-­‐time
reserves
and
inefficiencies
in
the
near-­‐term
asset
scheduling
and
curtailment
practices.
For
example,
the
integration
of
wind
energy
in
ERCOT
is
estimated
to
cost
an
additional
$0.66/MWh
due
to
deployment/operation
of
reserves,
the
cost
of
base
load
cycling,
and
transmission
congestion
(Ahlstrom,
2013).
In
terms
of
capital
outlay
for
reserve
capacity,
it
is
estimated
that
PJM
spends
$3
per
each
additional
MW
of
wind
power
capacity
(The
Brattle
Group,
2013).
The
renewable
integration
studies
have
found
that
these
practices
and
associated
costs
can
be
largely
avoided
if
the
grid
were
flexible
to
compensate
for
the
variable,
uncertain
supply.
Power
flow
control
technologies
can
achieve
sufficient
transmission
system
flexibility
to
lower
renewable
integration
costs,
reduce
congestion,
and
allow
for
even
further
economic
utilization
of
renewable
energy
by
minimizing
curtailment.
In
addition,
a
more
interconnected
and
controllable
transmission
system
will
facilitate
the
network
benefits
of
geographic
averaging
of
renewable
resources
and
more
accurate
wind
and
solar
forecasts.
Economic
Efficiency
Power
flow
control
technologies
can
increase
the
economic
efficiency
of
the
electric
grid
through
lower
losses
and
by
enabling
economic
dispatch
of
transmission
and
generation
assets.
HVDC
devices,
DSRs
and
TCAs
can
be
installed
on
the
existing
transmission
grid
to
allow
for
the
necessary
flexibility
to
lower
integration
costs
through
the
mitigation
of
curtailment-­‐causing
system
bottlenecks
and
congestion.
HVDC
Long-­‐distance
HVDC
installations
improve
market
access
to
remote
resources.
When
congestion
is
appropriately
managed,
HVDC
facilitates
lower
energy
prices.
Lower
line
losses
of
HVDC
can
further
15

16. reduce
the
overall
cost
to
serve
remote
load
by
30-­‐50%.
The
most
economic
generation,
including
renewable
generation
resources,
are
often
not
located
in
close
proximity
to
major
load
centers.
To
tap
these
resources,
a
transmission
system
must
be
developed.
For
long
distance
connection,
HVDC
conductors
offer
the
most
value
because
of
5-­‐10%
less
line
loss
than
similar
capacity
AC
conductors
(Bahrman,
2009).
Along
with
the
advantages
of
smaller
transmission
towers
and
no
need
for
intermediate
substations,
lower
line
loss
equates
to
lower
overall
system
cost.
For
a
1000
mile
system
rated
for
6000MW
an
800
kV
HVDC
system
is
$670/MW-­‐mi
less
expensive
than
a
765
kV
AC
system
(Bahrman,
2009).
HVDC
can
be
used
to
route
power
around
a
congested
area
of
the
AC
grid,
bringing
less
expensive
power
or
renewable
generation
situated
at
a
distance
to
market
in
an
area
of
higher
demand.
For
example,
the
Trans
Bay
Cable
delivers
power
from
Pittsburg,
California
to
San
Francisco,
providing
an
alternate
route
for
generation
to
serve
40%
of
the
city’s
peak
energy
needs.
Similarly,
the
Neptune
HVDC
cable
running
from
New
Jersey
to
Long
Island
enables
power
flow
directly
to
Long
Island,
skirting
areas
of
transmission
congestion
in
New
Jersey
and
New
York
and
serving
30%
of
electric
needs
of
Long
Island.
The
bi-­‐directional
flow
capabilities
of
many
HVDC
installations
could
allow
for
the
change
of
flow
to
address
particular
points
of
congestion
where
congestion
stress
points
shift
with
changing
supply
and
load
patterns.
For
example,
the
Cross
Sound
Cable,
a
merchant
transmission
line
between
CT
and
Long
Island,
largely
sends
power
from
CT
to
Long
Island
but
on
occasion
sends
power
the
other
way
in
response
to
changing
conditions.
Back-­‐to-­‐back
HVDC
–AC
intertie
capabilities
enable
ties
between
asynchronous
grids
and
can
thereby
increase
transfer
capacity,
allowing
for
access
to
supply
from
a
contiguous
grid
system
and
decreasing
the
cost
of
reliability
services.
HVDC
that
is
multi-­‐terminal
or
bi-­‐polar
with
bi-­‐driectional
capabilities
will
increase
the
interconnection
further
and
allow
for
economic
dispatch
in
multiple
directions.
For
example,
the
Cross
Sound
Cable
can
send
power
from
Connecticut
to
Long
Island
or
from
Long
Island
to
New
York
depending
on
system
conditions.
With
greater
HVDC
connectivity
of
disparate
renewable
generators
and
loads,
the
negative
system
effects
of
renewable
intermittency
are
largely
displaced.
Using
multi-­‐terminal
HVDC
transmission
systems
with
VSCs
that
allow
bi-­‐directional
power
flow,
system
operators
can
take
advantage
of
varying
geographical
resource
profiles.
For
example,
the
proposed
Clean
Line
Energy
transmission
projects
leverage
periods
of
excess
wind
energy
in
the
SPP
to
deliver
power
to
MISO
or
PJM
(Galli,
2012).
When
SPP
is
not
producing
wind
energy,
MISO
might
be,
or
likewise
PJM
might
be
producing
solar
energy.
By
connecting
large
geographical
areas,
the
average
amount
of
energy
available
to
serve
loads
is
higher
and
more
predictable
than
an
individual
resource
area
alone;
and
HVDC
systems
are
the
most
cost-­‐efficient
manner
to
create
the
connection.
The
geographical
averaging
effect
improves
energy
forecasts
(as
forecast
error
is
smaller
for
larger
geographies),
reduces
the
system
impact
of
ramp
events,
and
thus
reduces
base
load
cycling
and
the
use
of/need
for
reserve
capacity.
Additionally,
a
more
interconnected
transmission
system
allows
for
reserve
capacity
sharing
between
balancing
areas,
which
reduces
the
total
reserves
required
below
that
which
any
single
balancing
area
would
need
to
carry
to
meet
load
and
frequency
regulation
requirements.
16

17. HVDC
collection
systems
enable
a
new
design
paradigm
for
renewable
energy
generation
stations.
With
AC
collection
systems,
solar
PV
electricity
is
collected
as
DC
at
each
panel
and
then
converted
to
synchronous
AC
electricity.
For
wind,
generators
produce
asynchronous
AC
electricity,
which
is
converted
to
DC
and
then
to
synchronous
AC
electricity.
If
renewable
generators
were
designed
to
connect
to
an
HVDC
collection
system,
PV
panels
would
not
need
an
inverter
and
wind
turbine-­‐side
converters
would
be
reduced
in
complexity
to
output
DC.
This
not
only
reduces
the
costs
of
developing
renewable
generator
stations
-­‐
by
7%
for
solar
(Goodrich,
2012)
-­‐
it
also
lowers
the
collection
losses
when
there
are
long
feeder
lines
connecting
the
generators
to
the
transmission
system.
Vestas
estimates
a
30%
improvement
in
reducing
energy
losses
for
wind
farms
developed
for
HVDC
collection
instead
of
AC
(Manjrekar).
Power
Transmission
Controllers
and
Topology
Control
Algorithms
DSRs
and
topology
control
algorithms
could
increase
the
flexibility
of
the
transmission
grid
and
thereby
increase
the
economic
efficiency
of
generation
dispatch.
DSRs
allow
operators
to
bypass
congested
lines
by
increasing
capacity
and
distributing
power
flow
among
portions
of
the
AC
grid,
thereby
increasing
transmission
utilization,
decreasing
congestion,
and
allowing
for
economic
dispatch
of
generation.
For
instance,
variable
impedance
devices
such
as
Smart
Wire
Grid’s
DSRs
can
increase
AC
transmission
system
utilization.
A
Smart
Wire
Grid
simulation
of
3,000
modules
on
six
transmission
lines
in
an
eastern
RTO
reduced
the
average
bus
marginal
cost
by
over
6%
in
a
summer
peak
scenario
(Smart
Wire
Grid,
2013).
DSRs
balance
the
load
being
transmitted
across
each
phase
and
allow
for
the
increase
in
transmission
capacity.
Power
flow
control
technologies
designed
to
alleviate
congestion
can
have
a
great
advantage
to
easing
the
integration
of
renewables.
Smart
Wire
Grid’s
DSRs
have
been
demonstrated
to
create
a
variable
impedance
transmission
network
that
allows
power
flow
to
bypass
congested
lines.
A
simulated
study
in
the
Pacific
North
West
found
that
with
an
investment
of
$58
million
(~3000
devices),
the
variable
impedance
system
created
was
able
to
unlock
and
additional
2.8GW
of
wind
energy
by
reducing
congestion
(Smart
Wire
Grid,
2013).
This
benefit
would
be
achieved
without
adding
any
additional
transmission
lines,
and
thus
deferred
significant
investment
for
the
transmission
owners.
Likewise,
this
same
effect
can
be
accomplished
by
optimally
switching
transmission
lines
to
change
the
impedance
characteristics
of
the
transmission
system.
TCAs
can
be
deployed
by
system
operators
to
optimize
their
switching
decisions
based
on
real-­‐time
events
on
the
grid.
TCA
simulations
in
power
flow
modeling
software
has
shown
a
reduction
in
wind
curtailment
instances
from
33%
to
14%
by
switching
lines
(Qiu,
2013).
A
simulation
of
the
impact
of
TCA
using
historical
PJM
data
demonstrated
over
$100M
in
annual
savings
from
congestion
relief
(The
Brattle
Group,
2013).
Again,
these
benefits
were
gained
with
very
little
capital
investment
which
allows
transmission
owners
to
invest
elsewhere
in
their
system.
Other
HVAC
PTC
devices
that
can
provide
voltage
and
frequency
support,
such
as
STATCOMs
and
phase-­‐
shifting
transformers,
have
been
used
to
improve
the
integration
of
wind
and
solar
generators.
These
devices,
which
also
allow
for
power
flow
control,
provide
dynamic
response
to
fluctuations
in
the
power
quality
of
renewable
generators.
17

18. Summary
of
Power
Flow
Control
Technology
Value
One
power
flow
control
technology
can
have
multiple
benefits
depending
on
its
application
in
the
grid.
To
understand
the
possibility
of
various
power
flow
control
technologies
at
a
glance,
see
Table
1.
Technical
capabilities
alone
are
not
sufficient
to
achieve
economic
efficiency
of
the
system
with
the
deployment
of
a
power
flow
control
technology.
Market
and
regulatory
barriers
can
prevent
use
of
the
technical
capabilities
even
when
it
would
be
economic,
highlighting
the
need
for
clear
understanding
among
transmission
owners,
system
operators,
and
regulators
of
both
technical
capabilities
and
benefits
of
technology
at
the
system
level.
Table
1.
Power
Flow
Control
Technology
Value
Categories.
Power
flow
control
technologies
can
have
different
or
multiple
benefits
depending
on
their
position
and
application
in
the
electric
grid
–
asset
management,
renewable
integration,
congestion
relief,
economic
efficiency,
and
reliability
and
security.
Classes
of
technologies
that
are
represented
by
one
or
more
of
ARPA-­‐e’s
GENI
technology
teams
are
represented
in
bold
font.
GENI
Technology Value Categories
X
HVDC LCC
X
X
X
X
X
TCSC
X
X
X
X
X
X
X
X
X
X
X
UPFC
Real Time
X
Dispatch &
planning
X
Reduce
curtailment
X
X
HVDC VSC
Improve
Contingency
Reliability
&
Security
Ancillary
Economic
Efficiency
Energy
Congestion
Relief
Black start
Renewable
Integration
Improve inter –
connection
Prioritize or defer
new investment
Value
Asset
Management
Improve
Utilization
Power Flow
Control
Technology
Non-GENI
Shunt -STATCOM
Series - SSSC
X
X
X
X
X
X
X
X
X
X
PhaseShifting
Transformer
X
X
X
X
DSR
X
X
X
X
TCA
X
X
X
X
X
X
X
X
X
22
Stakeholders
in
the
Transmission
Grid
Influence
Technology
Investment
Decisions
As
previously
discussed,
quantifying
the
benefits
of
power
flow
control
capabilities
is
particularly
difficult
due
to
the
dynamic
nature
of
the
electric
transmission
grid
and
the
differences
in
benefits
to
individual
stakeholders
as
compared
to
the
overall
system
benefits.
At
the
same
time,
multiple
18

19. stakeholders
are
often
involved
in
technology
investment
decisions,
and
a
level
of
agreement
among
them
is
necessary
in
order
to
optimize
system
efficiency.
Differences
in
regulatory
structure
among
federal
power
authorities,
investor
owned
utilities,
merchant
transmission
owners,
municipal
utilities,
and
rural
electric
co-­‐ops
lead
to
substantial
differences
in
the
way
certain
groups
assess
power
flow
control
technologies,
even
within
similar
stakeholder
categories.
As
technology
vendors
consider
the
best
value
proposition
and
business
model
for
their
power
flow
control
technologies,
they
should
bear
the
regulatory
environment
and
degree
of
restructuring
of
the
electric
market
in
mind.
For
an
overview
of
influencers
in
the
electric
grid,
see
Figure
2.
Numerous influences on Transmission Owner’s
investment and siting decisions
ISO/RTO
NERC/
coordinating
councils
$
Tech
Transmission
Owner
Decreasing
influence
on
investment
decisions
Transmission CAPEX,
OPEX, rate recovery
FERC
PUC
Regulatory
industry groups
Other
regulators,
NGOs
16
Figure
2.
Overview
of
influencers
in
the
transmission
grid.
A
utility
or
transmission
owner
investing
in
technology
must
be
mindful
and
responsive
to
the
interests
of
multiple
stakeholders
in
the
grid:
the
ISO/RTO
that
dispatches
assets
and
determines
set
points
for
power
flow
control
technologies,
the
regulators
overseeing
investment
and
siting
decisions,
the
bodies
responsible
for
overall
reliability
of
the
electric
grid,
and
other
interested
parties
who
may
intervene
in
a
transmission
case.
The
benefits
of
power
flow
control
technology
to
each
stakeholder
will
vary
by
their
business
model
and
geographic
and
regulatory
situation.
To
better
understand
the
business
models
and
motivations
of
various
stakeholders
in
the
electric
transmission
grid,
see
Table
2.
For
the
most
part,
power
flow
control
will
have
positive
economic
outcomes,
with
the
exception
of
those
stakeholders
who
currently
benefit
from
transmission
congestion
such
as
reserve
generators
and
to
a
slightly
lesser
extent
base
load
generators,
renewable
energy
generators,
and
transmission
owners.
19

20. The
beneficiaries
of
a
change
in
power
flow
control
will
often
be
temporary
and
largely
situation-­‐
dependent,
as
market
conditions
will
remain
dynamic
in
a
world
with
power
flow
control.
An
overview
of
how
each
stakeholder’s
situation
might
change
as
compared
to
current
conditions
is
presented
in
Table
3.
Table
2.
Motivations
of
stakeholders
in
the
electric
transmission
grid.
This
table
demonstrates
the
motivations
of
each
stakeholder
involved
in
the
electric
transmission
grid,
including
their
motivations,
inherent
conflicts
and
considerations,
and
a
brief
description
of
their
revenue
model.
While
every
effort
was
made
to
provide
a
comprehensive
overview,
the
differences
in
regulatory
structure
among
federal
power
authorities,
investor
owned
utilities,
merchant
transmission
owners,
municipal
utilities,
and
rural
electric
coops
should
be
considered
when
assessing
the
position
of
each
stakeholder.
Stakeholder How do they
Conflictsmakeinterest related to
of or recover $ Motivation
Conflicts & Considerations
PFR investment
Transmission
Owner
§ Rate of return (~13%) for
transmission investment
§ FERC technology
incentive rate
§ ~11.5% distribution
investment
§ Projects that will be approved or financed –leads
to incremental build out of system (relatively
short time horizon for utilities dependent on
regulated rate of return)
§ Invest in what they know (wires) rather than new
technology
§ Profit
§ Incentive towards construction to meet
peak - of new transmission lines rather
than investment in technology to
remove congestion etc.
§ Regulated: certainty of public benefit
case (to rate-base)
§ Merchant transmission need 20 year,
low-risk opportunity
ISO/RTO
Fees charged to:
§ Generators
§ Transmission owners
(allocated to states and
recovered in rate base)
§ Reliability (& compliance with standards)
§ Reduced congestion
§ Reserve margin
§ Economic efficiency
§ Known solutions
Split in priority/focus :
§ Reliability
§ Economic dispatch
§ Capacity margins
Renewable
Generator
§ Contracts (PPA, tariff)
§ Bankability
§ Off-take certainty
§ Reduced curtailment
Base Load
Generator
§ Dispatch
§ Regulated return (where
applicable)
§ Bankability
§ Increase utilization
§ Compliance with regulations
§ Risk change schedule/dispatch
§ No compensation for cycling & wear &
tear for slow ramping
Reserve /peak
Generator
§ Dispatch
§ Ancillary services
§ Regulated return (where
applicable)
§ Increase utilization
§ Ability to access ancillary services revenue
streams (where applicable)
§ Compliance with regulations
Risk lowering utilization by removing
ancillary service functions
FERC
§ Congressional approval
§ Recovered from
regulated industries
§ Economic efficiency
§ Reliability
§ Policy implementation
TO needs to approach FERC with new
technology to receive favorable return for
new tech solution. Theoretically could
change incentive for transmission
technology investment over new wires.
PUC
§ Budget set at state level
§ Recovered from rate
payers.
§ Customer rates
§ Economic efficiency
§ Reliability
§ Policy implementation
§Transmission investment on economic
benefits accruing to their state rate
base vs everyone else in market area
§ Public perception
§ Re-election (where applicable)
ARPA-E Template
19
20

21. Table
3.
Overview
of
beneficiaries
as
a
result
of
power
flow
control
improvements
in
the
electric
grid.
Power flow control technology
beneficiaries
Benefit is dependent on situation
Revenue losses likely in current system
Black start
Reliability &
Security
Improve
Contingency
Ancillary
Economic
Efficiency
Energy
Real Time
Congestion
Relief
Dispatch &
planning
Reduce
curtailment
Renewable
Integration
Improve inter
–connection
Prioritize or
defer new
investment
Value
Asset
Management
Improve
Utilization
Stakeholders
Likely benefit (financial or operational)
Transmission Owner
ISO/RTO
Renewable
Generator
Base Load
Generator
Reserve Generator
FERC
PUC
Consumer
PFC generally produces beneficiaries…except in cases where stakeholders
currently profit off of system inefficiencies
Conclusion/Next
steps
This
document
defined
power
flow
control
and
identified
and
described
technologies
that
enable
power
flow
control.
It
identified
the
benefits
of
power
flow
control
and
how
these
benefits
accrue
to
various
stakeholders
involved
in
the
electric
grid.
It
did
not
perform
a
detailed
analysis
of
system-­‐level
benefits
or
provide
case
studies
quantifying
the
impact
of
power
flow
control
technologies.
As
power
flow
control
technologies
become
more
common
on
the
electric
grid,
further
analysis
will
be
required
to
optimize
their
use
at
a
system
level.
This
should
include:
Technology
case
studies
and
models
•
Power
flow
control
technology
case
studies
and
data
sharing
to
document
lessons
learned
For
the
existing
cases
where
power
flow
control
technologies
are
installed
and
operated,
in-­‐
depth
analyses
will
advance
the
understanding
of
the
technical
capabilities,
costs,
and
benefits
of
the
technology.
Where
possible,
case
studies
should
include
quantitative
analysis
of
the
21

22. •
•
•
effects
of
the
technology.
Data
sharing
at
a
high-­‐level
will
enable
deeper
understanding
of
the
applications
of
power
flow
control
technologies.
Possible
case
studies
include
o HVDC:
 Trans
Bay
Cable
and
its
use
and
effects
on
transmission
congestion
 Bi-­‐polar
HVDC
applications
such
as
Cross
Sound
Cable
between
Connecticut
and
Long
Island,
Cross
Chanel
Cable
between
the
UK
and
France
o UPFC:
 Marcy
station
UPFC
in
New
York.
What
was
the
economic
(market)
response
to
its
operating
mode
set
points,
before
and
after
installation
o DSR:
 Case
study
on
the
Tennessee
Valley
Authority
pilot
installation
Further
describe
and
quantify
the
benefits
of
power
flow
control
technology
to
a
particular
stakeholder
Interested
parties
will
seek
more
information
on
how
the
benefits
of
power
flow
control
technologies
change
the
economics
of
the
system,
particularly
for
cases
where
the
benefits
of
a
power
flow
control
vary
(e.g.,
those
situation
identified
as
“yellow”
in
Table
3–
in
what
situations
are
these
green
and
red?)
Develop
or
identify
a
uniform
model
for
analyzing
transmission
technologies
Numerous
stakeholders
expressed
interest
in
a
uniform
grid
model
of
sufficient
size
to
model
system-­‐level
effects
of
combinations
of
technological
installations.
Add
power
flow
control
technology
specifications
to
existing
grid
modeling
software
Recent
modeling
exercises
may
have
been
limited
by
the
technical
specifications
available
to
modelers.
To
the
extent
that
these
set
points
can
be
added
rather
than
programmed
for
each
specific
hypothetical
or
actual
installation,
decision
makers
would
have
more
accurate
models
and
understanding
of
the
effects
of
technological
installations.
System
level
technical
and
market
analyses
•
•
•
Technological
analysis
of
what
is
required
to
enable
power
flow
control
at
a
system
operator
level
Analysis
may
include
modeling
of
optimal
physical
positioning
of
devices
in
the
grid,
reliability
modeling,
and
economic
modeling
of
the
impact
of
increased
transmission
capabilities
and
the
increased
fluidity
of
changing
grid
topologies.
Define
level
of
coordination
and
control
required
within
an
RTO
and
among
regions.
In
order
to
increase
the
flexibility
of
the
transmission
and
distribution
grid
and
meet
goals
around
reliability,
integration
of
renewable
electricity
at
the
utility
and
distributed
scale,
energy
efficiency
and
demand
response
capabilities,
we
will
need
some
centralized
control
and
centrally
coordinated
distributed
control.
This
will
provide
quick,
responsive
voltage
support
and
meet
the
changing
needs
of
the
electric
grid.
Consideration
of
market
design
for
a
flexible
transmission
grid
Changing
grid
topologies
can
change
the
economics
of
generator
and
transmission
positioning
22