Decoupled symmetrical component
frame power system models for
smart grid application
Khalid Mohamed Nor
Mamdouh
Abdel
Akher
Syafii
Universiti
Teknologi
Malaysia
2011
•
Background
•
Power system models
•
Application
–
Fault analysis
–
Load Flow
–
Harmonic penetration study
•
Parallel computing
2
Presentation outline
•
The penetration of distributed generations (DG)
and distributed storage (DS), together known as
distributed energy resources DERs, changes
conventional distributions systems to active
distribution systems (ADS.
•
To operate ADS efficiently, they need to have the
ability to monitor many states and variables of
the network.
•
The Smart grid concept via the continuing
technological development and improvement in
communication technology, control devices and
instrumentations will provide the facilities.
INTRODUCTION
•
One of the important requirements for the ADS
planning, operation and control, is an accurate
steady

state analysis, such as power flow and
fault analysis.
•
The conventional power

flow analysis methods,
that are widely used for large power transmission
systems are based on the system positive

sequence representation.
•
These methods are deemed to be inaccurate for
unbalanced networks with single

phase laterals,
single and two

phase loads, centre tapped
transformer loads and unbalanced three

phase
loads as well as single

phase and three

phase
DERs.
INTRODUCTION
•
Many unbalanced system studies are analyzed based
on detailed three

phase network representation.
•
Three

phase power

flow methods that are
formulated based on phase components include two
categories.
•
Firstly, methods consider primarily the radial
structure of distribution networks.
•
Secondly, the method based on Newton

Raphson
technique has been applied for general network
structures.
•
In contrast to the general network structure
problem, the forward

backward sweep method, and
the compensation method solves for load flow
analysis of the system radial feeders and weakly
meshed grids methods based on the phase frame
approach.
Depending
on
reference's
frames,
the
three

phase
power
flow
formulation
can
be
modelled
using
phase
component
approach
and
sequence
component
approach
.
The
phase
component
using
forward/backward
method
[
Kersting
W
.
H
.
,
2001
,
Khusalani
S
.
,
et
.
at
,
2007
]
cannot
deal
with
a
highly
meshed
system
(IEEE
118
and
300
bus
test
systems)
.
The
sequence
component
using
Newton
Raphson
based
method
[Abdel

Akher
M
.
,
et
.
at,
2005
]
can
solve
load
flow
of
three
phase
unbalanced
system,
radial
and
meshed
systems
.
It,
however,
cannot
account
for
multi

phase
laterals
.
The
forward/backward
is
used
in
handling
multi

phase
lateral
.
This
method
will
lose
its
computational
advantage
when
dealing
with
a
large
number
of
laterals
systems
(IEEE
8500
test
system)
.
INTRODUCTION
The
focus
of
this
paper
is
to
develop
a
symmetrical
component
based
models
for
a
general
large

scale
network
.
The
models
can
be
used
to
analyse
general
network
that
contains
almost
all
practical
distribution
system
features
with
composite
meshed
network
and
radial
feeders
.
The
algorithm
has
included
steady

state
DG
models
and
center

tapped
(CT)
transformer
load
model
.
The
DG
models
that
have
been
developed
include
cogeneration,
photovoltaic
and
wind
turbine
generator
.
The
voltage

controlled
and
complex
power
injection
node
models
are
considered
.
The
network
structure
to
be
full
decomposed
which
is
amenable
to
implement
parallel
computing
Symmetrical
component
models
of
three
phase
system
is
well
established
.
The
modelling
accounts
for
four
wire
systems
as
well
ground
wires
.
The
following
slides
give
details
on
decoupling
techniques,
multi

phase
laterals
line
model,
DG
models
and
centre

tapped
(CT)
transformer
load
model,
which
are
not
covered
in
the
classical
symmetrical
component
modelling
.
Power System Model
9
The
admittance
matrix
of
symmetrical
component
of
unbalanced
system
has
off

diagonal
elements
.
In
order
to
decouple
the
symmetrical
component,
AbdelAkher
and
KM
Nor
have
proposed
method
compensation
.
DECOUPLING OF SYMMETRICAL COMPONENTS
Y V
=
I
Representation of multi

phase system using dummy lines and nodes
The biggest challenge of applying decoupled symmetrical
components is the modeling of multi

phase lines.
M. Abdel

Akher, and K. M. Nor, “Fault analysis of multiphase
distribution systems using symmetrical components”,
IEEE
Transactions on Power Delivery
, Vol 25, Oct 2010
Synchronous Generation Based WTG Model
By knowing of injected power and voltage magnitude at a generator bus, the
WTG can be modelled as voltage controlled device. If the Q limit is used, the
PV model will be automatically converted to a PQ model.
1. Regulation excitation voltage model as
PV node
2. Fixed excitation voltage model as
PQ node
(Round rotor SG)
The WTG power output is can be determined from the power

speed curve
provided by its manufacturer, such as:
0
100
200
300
400
500
0
2
4
6
8
10
12
14
16
18
20
22
24
Power (kW)
Wind Speed (m/s)
Vestas V39 500 Power Curve
Wind Turbine Generator Models
Wind Turbine Generator Models
Induction Generator Wind Turbine
Active
power
output
obtain
from
the
power
curve
of
the
WTGU
(provided
by
the
manufacturer)
for
given
wind
speed
.
Q is found by solving as follows.
The
reactive
power
consumed
depends
on
node
voltage
at
WTG
connection,
which
is
updated
during
power
flow
iteration
process
.
Photovoltaic Models
The
voltage

current
(VI)
equation
of
PV
device
given
by
:
I
pv
is
function
of
solar
radiation
and
temperature,
I
0
dependence on the temperature
Power output is given by
Parallel Processing Implementation
The
decoupled
symmetrical
component
models
are
inherently
paralleable
.
Nowadays,
multi

core
processor
chip
has
brought
parallel
computing
to
the
ubiquitous
PC
.
It
means
that
the
hardware
cost
is
the
same
,
whether
used
as
a
serial
processing
system
or
a
parallel
processing
system
The
parallel
algorithm
developed
using
visual
C++
programming
under
Visual
Studio
2008
with
an
OpenMP
and
Intel
C++
compiler
to
support
parallel
processing
.
OpenMP
(Open
Multi

Processing)
provides
parallel
processing
using
thread
based
and
shared
memory
parallel
programming
.
From the decoupled symmetrical component models, we
can construct matrices, Y
1
, Y
2
and Y
3
, which correspond to
the positive, negative and zero sequence admittances
respectively.
Y
1
V
1
=
I
1
Y
2
V
2
=
I
2
Y
0
V
0
=
I
0
Once the sequence networks have been determined,
computation of the unbalanced faults which have been well
Established can be applied.
In fact, any unbalanced fault analysis commercial software
can use the models proposed to analyse any three phase
unbalanced networks with multi

phase feeders.
Unbalanced fault analysis
16
Parallel sequence component three

phase power

flow algorithm
The
problem
decomposed
into
tasks
.
These
tasks
can
be
worked
on
independently
of
the
others
and
run
under
the
multiple
processors
system
.
The
problem
that
can’t
be
decomposed
will
use
parallel
loop
.
17
Incorporating CT Transformer Load Model
The
unbalanced
load
connected
to
center

tapped
transformer
via
service
lines
solved
using
voltage
drop
analysis
in
three

phase
load
flow
iteration
.
The
CT
Transformer
Load
modelled
as
power
injections
S
ab
=
S
l1
+S
l2
.
V
ab
from power flow calculation.
The
proposed
algorithm
is
validated
by
comparing
with
forward/backward
sweep
method
using
a
radial
distribution
analysis
package
(RDAP)
for
the
original
of
37
node
feeder
and
IEEE
13
node
feeder
.
The
results
are
the
same
correct
to
significant
figures
.
RESULT
AND
DISCUSSION
Tests to show the
ability of method to
handle meshed and
radial feeders is
carried out by solving
a composite test
system which is a
combination of Taiwan
Power company 24
b(unbalanced three
phase system) and
radial feeder networks
The
new
development
in
distribution
system
analysis
tools
needs
to
test
the
robustness
of
their
algorithm
using
IEEE
8500

node
test
system
.
This
system
is
a
latest
data
(published
2010
)
by
IEEE
PES
distribution
system
analysis
subcommittee
used
to
test
the
robustness
of
the
algorithm
for
large
system’s
problem
.
Performance in Solving Large

Scale Distribution System
The Results of Modified TCP 24 Bus with DG
DG Impact Analysis of IEEE 8500 node test case
Performance results of IEEE 8500

node test case under 2.66 GHz PC
The proposed algorithm can be
extended for solving repetitive
applications in power system
analysis such as fault analysis with
contingency assessments and three

phase harmonic power flow study.
The speedup advantage from parallel
programming can be significant in
larger

scale power system problem.
.
The network harmonic admittance
matrix can be obtained by calculating
the impedance at each harmonic
frequency,
The following Equation is used to
solve for harmonic voltage for each
harmonic frequency:
Unbalanced Harmonic Penetration
The
decoupled
symmetrical
component
frame
power
system
models
has
been
succesfully
used
to
all
components
of
active
distribution
systems
.
The
DG
models
that
have
been
considered
are
cogeneration,
PV
and
WTG
.
The
variation
of
wind
speed
(m/s)
for
WTG,
solar
radiation
(W/m²)
and
temperature
(
C)
for
PV
have
been
simulated
.
Load
flow
solver
using
the
models
has
been
benchmarked
against
commercial
software
for
the
three
phase
load
flow
and
also
compared
with
a
forward/backward
method
.
It
shows
that
the
proposed
method
has
good
convergence
properties,
accuracy,
efficient
and
robustness
.
Summary
The
simulation
results
show
that
the
proposed
DG
model
can
be
used
to
analyse
DG
impacts
in
the
unbalanced
meshed
and
radial
distribution
system
.
The
analysis
using
proposed
decoupled
model
has
significant
computing
parallelism
which
has
been
exploited
in
a
multi

core
PC
Based
parallel
programming
for
sequence
decoupled
three

phase
power
flow
analysis
.
The
parallel
execution
of
the
proposed
algorithm
produced
computational
speedup
The
analytical
tools
using
the
decoupled
symmetrical
components
can
be
used
to
for
planning
and
operation
of
ADS,
i
.
e
used
as
an
analytical
component
of
a
smart
grid
.
Future Work
The
optimal
DG
size
and
location
have
not
been
considered
yet
.
The
optimization
methods
to
determine
the
optimum
size
and
an
effective
methodology
to
identify
the
best
location
for
DG
placement
can
be
investigated
in
further
research
.
Thank you
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