Intelligent
—
Control
Methods
for Systems with Dispersed
School of Electrical
Engineering
and Computer
Washington
State University,
Pullman,
tomsovic@,eecs. wsu.edu
Abstract:
Recent
technology
and energy storage
generators
opportunity
for dispersed
Department
Science
improvements
in small
devices have provided
new
decentralized
approach
to power
proposes some approaches to power
delivery.
This
paper
system operations and
security
and
associated
simulation
environment
are presented showing
A methodology
operations
is
a more
for system
introduced.
Dispersed
intelligent
strategies,
energy resources,
distribution
system
controls.
increasingly
industry,
promises
technologies,
reliability
to transform
including
storage
of the electric
the delivery
of distributed
fuel
devices,
cells,
available
been receiving
particular
from
attention
communications,
low
the
resources
better
primarily
cost
controls
economics
utility.
From
have
need
new
in the form of the intemet,
offer
for the distributed
subsystems are likely
that is, similar
to
of reliability
Note
circuits
and supply
reliability,
on the local
these units
and infrastructure
of a significant
in
the
sources.
distribution
extant
[6]. The wide
single point
failures
is that the new structure
for lower
penetration
could
under appropriate
In this
paper,
control
is discussed.
an overall
testing
various
framework
A simulation
structures
and
for
II. DISTRIBUTION
SYSTEM
static
evaluation
Security
refers
contingencies
problems.
of a system’s
to
the
of DER
analyzed
in the
ability
system’s
generator
units
independently
will
proposed
be responsible
dispatched
but
sources for normal
operation.
ancillary
services,
such
support,
as well
include
time-of-use
reliability,
Each
APS
example,
pricing,
may
of
such
and still maintain
dependent
load
various
following
possible
location
and
community
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IEEE
IEEE
[5]
limits.
by
This
to supply
different
of
to
on operations.
enter
the load.
withstand
service to all customers
Traditionally,
and
these have been
to have a
but occur rarely)
and vice versa.
while
In the APS architecture,
distribution
System
systems
security
security
analysis
is
can
for the first
Security
services
A variety
dependent
[8].
indices
indices,
For
may desire a low capacity
913
which
for a distribution
These indices
categories:
single load point
indices,
and load orientated
capacities,
service.
of reliability
been defined
and reserve supplies.
quality
is introduced.
framework.
system (say, in a system where critical
are numerous
2.1 Distribution
or voltage
new
and price
effectively
time.
and
The units can supply
Other
An
as separate issues and it is quite possible
but insecure
focused
a system,
outside
be characterized
a residential
In
or
on
functions
operation
systems
for “nearby”
still
as, load
as energy.
maintenance
independence
[4].
for
philosophies.
capability
In general, adequacy is focused on planning
been
and
Power
system
reliability
can be classified
into
two
components:
security and adequacy [7]. Adequacy
is the
contingencies
has
of the various
OPERATIONS
of several
microgrids
The
improve
the security
control
example system using intelligent
controls
highlights
the philosophy
of the proposed
can help
composed
power
to
accepts
has been developed
(APS)
autonomous
greatly
operation
operations.
The concept of a distributed
exposure
cost, leads to this result.
reliable
connected
system,
customer
design, which
near future suggests more focus must be placed on effective
loosely
power
unavailability
and the radial structure
this performance
As such,
system
over 90°A towards
respect all equipment
The possibility
to
to be primarily
the traditional
contribute
expectation
allow
energy
service
dependence
perspective,
subsystems
of services.
distributed
improved
and a reduced
the utility’s
address a number
[1-3],
costs and limited
addition,
In
perspective,
can
a
user needs.
vendors
and a diversification
customer’s
(DER)
here is on the
subsystems.
due to the competitive
pricing of natural gas, low installation
for
maintenance
overhauls.
in operating
The emphasis
and new
offering
for meeting
several
and
generation
available,
characteristics
utility
of power
power
microturbines,
are currently
Microturbines,
From
of such systems. As
problems
as a whole.
analysis.
harsh elements
nature
A number
variety of performance
very
effectively
distribution
competitive
services.
energy
or “intelligence,”
be operated
outage
energy
the operation
the power system with an APS.
These interconnected
radial
in structure,
I. INTRODUCTION
The
for understanding
such, this paper poses some important
distribution
system, but with multiple
analysis
begins
from
traditional
Keywords:
Japan
A
has been developed.
Some results
the effectiveness
of the new control
methods.
security,
Engineering
Kumamoto,
system with relatively
frequent interruptions
at a low cost.
The currently
available
analysis
tools provide
no good
methods
has encouraged
level.
and Computer
University,
hiw=una@,eecs.kumamoto-u.ac.ip
energy resources at the distribution
at the distribution
of Electrical
Kumamoto
WA
level. At the same time, deregulation
control
Generation
T. Hiyama
K. Tomsovic
provide
indices,
indices.
service
system have
can be divided
into three
customer orientated
Single
load point
reliability
data
from
an
individual
customer
viewpoint,
are the average
failure
rate
as,
difference
in design
process
that cannot
APS are not only independent
in terms of business
(1)
barrier
to optimizing
among
owners
optimize
where n is the set of components
whose failure
outage at the given load points
critical
components
within
and Ii
results
is the failure
in the APS will
the overall
reliability
a section i.
The question
normally
provides
of the
reduces
if
overall
disturbance
lead to a customer
requires
outage.
that
That measure
no
is not
necessarily
another
unit
damping.
operate
expected
an individual
In
A radial
fault
The following
traditional
reliability
definition
is proposed
measures with security.
lead to an outage and n+-1 secure fno
between
a loads section
and the substation
fault
will
for
lead
Systems
operation,
determine
system
Thus, if protection
systems would
can island
is set correctly,
be operated
to support
generation
could be n+l
also that the system may become
downstream
generators
most present distribution
the
n-1 secure but only systems that
n-1 insecure
to cover capacity
IPSS
dynamics.
stabilization
systems
then adequacy
Let Pi be the maximum
maximum
on a section
in section
i, if
i and Pim= the
downstream
fi-om
the
authors
rule
III. SIMULATION
domain
i=l
environment
computing
(2)
sofiware
software
tools
perform
the
following,
models
whose failure
would
is achieved
by having
sufficient
oriented
unquestionable
adequacy
importance
related to reliability,
indices.
for
Security
operations
but
will
be of
should
be
that is, risk of outage, to be meaningfid
the
The
above
structure
of
concern
focus on development
of new
measures of reliability
and new tools for designing systems
based on these measures; however, there is an overriding
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2000
2001
IEEE
IEEE
have
logic
of
such
descriptions
models
been
MATLAB@.
appropriate
of
[e.g., 9].
developed
in
purpose
in
of
their
available
ability
to
In
the
simulations.
is developed
the
technical
Commercially
limited
type
structure
based on the
Models
models using time domain characteristics
For reasons of efficiency,
an unbalanced
power flow algorithm
using standard phasor
was integrated
was then developed based on [1 O]
calculations.
This load flow model
with time domain
For efficient
the load flow
Controls
areas
fizzy
stability
of the general
generally
a control
studies.
for most customers.
2.3 Intelligent
are
Detailed network
were developed.
capacity. A different
level of security could
each load point, i.e., customer, as is done with
the customer
robust
system
employed.
3.1 Network
for n+ 1 security
downstream
characterize
ensure
on overall
cut off supply
from the subsystem.
Operations
to
an
within
ENVIRONMENT
simulations
SIMULINK@
where m are components
propose
investigated
analyzed
of general
and
includes
The controls
controls
have
and
This
authors
System (IPSS).
or no information
control
operation
i
Time
i=l
of
not
system
data as well as physical
vein,
logic
are
observe
measures need to be redefined.
loading
generation
can
mode
systems rather than precise analytical
For islanding
is
centralized
control
algorithms.
to market
fuzzy
in terms
and
current
In this
limited
The
to
subsystem
it’s own operations
that
appropriate
respond
include
secure. Note
limits.
the
select
given
if it relies
on
needed
Power Supply
response
Accordingly,
traditional
operation
are
parameters.
Intelligent
will
information
each
to control
environment,
design,
systems that will
uncertainty.
Here,
that
subsystem
from the substation.
adequate.
subsequently
to an outage.
greater
that
in a manner
Each
to ensure adequate
system.
uncertain
algorithms
system is n-1 secure zfno single downstream
will
this
support
a controller
for some unit may
responds
to act autonomously
but receive
customer.
under
a functioning
practical
for a radial system even with multiple
sources.
Further, security is a system viewpoint
of little relevance to
that combines
conflict
necessary to
can be made on the
stabilization
system
sustain
security
Information
For example,
effective
system
of
be a significant
if interests
may not be available.
information.
there must be guidelines
definition
will
arises as to what decisions
basis of “local”
subs ystem to disturbances
upstream and downstream
and
two, the ability of an islanded subsystem to supply load. The
level
There
the performance
The
but also
in an
rate of
depend on: one, the exposure
ownership.
of the subsystems.
be ineffective
Security
be neglected.
in terms of operation
models for use in operation
computations
calculations
in time
are conducted
then the time integration.
This is allowable
deviations
integration
between
time
domain
studies,
at larger time steps
since the voltage
steps are quite
small.
Using
the
previous
time
step
voltage
solution
for
initialization,
convergence is usually within one forward and
except
if a large disturbance
(e.g.,
backward
sweep,
switching)
occurs.
914
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3.2 Source
At present,
models
high speed microturbines
Models
there are not standardized
for the different
might
find
for
large
types
and widely
of DER
synchronous
units,
under way to address these modeling
concerns
of
accepted
employed,
where available,
this
paper,
generally
control
Five
Efforts
[11].
For the
units within
the IPSS have governor
can still
sufllcient
line
one may
proposed
types
small
of
hydro
induction
energy
DER
source
units,
models
microturbines,
driven
by a wind
systems
(ECS)
for
capacitor
described
have
been
faults
are
example
presented
not
Mini
2.
turbine
short-term
in
and
storage.
simulations
Fig.
1 that
Kumamoto
6.6kV.
in the following:
hvdro
unit:
Standard
for the smaller
Microturbine:
hydro
unit models
are used
The system
speed type of unit is
in generally
slow
This is modeled
actively
on
The
load.
There
current
Photovoltaic:
the disturbance
current
A random
source is assumed that
model
for solar variation
the
Wind
Turbines
represented
with
asynchronous
as a non-linear
which
varies randomly.
output
variations
function
Control
generator
of the wind
is limited
that can be managed
are
These
relative
are
longer lifetimes
Costs
a new
to batteries,
through
technology
energy
storage
have recently
dropped
which
load following
frequency
deviation
and
generator
set points
[12].
that,
cycles.
They
as
system
Two
The
fimctions
mismatch
authors
to
have
systems
the feeder
used
adjust
proposed
that
line
the load following
a
neglects
flow
is
structure
is that this flow is measured
link exists with any unit
service. The obvious
is simplicity
In addition,
benefit
and need for
the following
deviations,
charging
mode
control
short
where
limits.
output
charge after
The objective
respond
Sustained
to match
the unit
to nominal
is to
duration.
the ECS runs in
or discharging
to
of
small
load
deviations
are
by the microturbine.
security
framework,
the system
along
the feeder
up, can be effectively
load, faults
beyond point A, at either B, load Ld7 or line section C, lead
to loss of service. The most securely operated points on the
have
are modeled
and regulation
tie-line
scheduled flow. The assumption
locally
and a communication
communications.
either
damped by response of the ECS. For the variable
scheduled to a particular point on the distribution
system and
the control signal is taken to be the mismatch
from the
the proposed
are
here), or elsewhere
Strategies
similar
concept
for distribution
frequency
deviation
[6]. Here,
supplying
an
and the ECS
to the proposed
are upstream
simulations
been verified
The traditional
for generation
from
the IPSS tends to benefit
and Communication
the end
operates as both n- 1 secure and n+l secure at each load up to
point A. Disturbances at the substation (response not shown
but much
dramatically.
times,
towards
is
the microturbine
followed
In reference
control
in terms of charge and discharge
extremely
fast response
instantaneous here.
3.3 Control
developed
has low
of 5 MW
and microturbine
has settled to within
of
unit
unit
following
eventually
level
speed,
to real power
of the rotor pitch blades.
~:
load
the
voltage
load. The IPSS contains
is zero. The ECS is restored
changes
units:
hydro
in
Only
is also a neutral
here as a slow ramp rate with a single time constant.
A constant
variable
shown
feeder
nominal
a small
For flow
mode
numerical
on the system
a distribution
includes
controlled.
continuous
is used.
5.
wind
the
Those
RESULTS
The IPSS is connected
for storage.
from
security.
in
are performed
area of Japan.
a solar cell,
ECS
The high revolution
is not controllable.
4.
oscillations
dynamic
demonstrated
is based
near the substation.
capacity.
modeled. These fast rotations result
mechanical
power output response.
3.
to damp
given
here.
of the feeder near a highly
adjusted
functions
so as to improve
fimctions
Numerical
photovoltaic
generators
These models are briefly
1.
following
IV. SIMULATION
different
units,
load
Here, none of the
speed-droop.
capacity.
method.
developed:
provide
regulation.
The ECS can be controlled
●
are
These models
control problems
effectively
the
for frequency
ECS
are
models
for the simulation.
do not address all the practical
encounter
but can demonstrate
.
say, as one
generators.
purposes
accepted
or in fuel cells) makes them in
appropriate
a security
cases are shown
using a detailed
stand point,
loads the most.
here. These results
analog
simulation.
have
In the first
case, only the microturbine
is controlled.
The load increases
for several seconds, returns to the initial
state and then
increases again. Fig. 2 and 3 shows the power inputs from
the
wind
microturbine
without
and
solar
and ECS
units
as well
response.
the ECS is shown while
as response
In Fig.
of
the
2, the response
Fig. 3 includes
the ECS unit.
The power flow at location A, the total real power output of
the IPSS and the variable load are given by P,,P, PiP and l’1~,
respectively.
of
A. From
nearby upstream
With
the ECS, the load changes
can very be
tracked very accurately.
limited
observations
are
V. CONCLUSIONS
made:
●
By neglecting
system
frequency,
frequency
relatively
low
the slow
ramp
inertia
concerns
regulation
of some
are
smaller
of interacting
with
minimized.
The
units
coupled
with
up rates for other units (for example,
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2000
2001
IEEE
IEEE
in
This paper discusses an approach for operating a distribution
system with
several
DER
units
controlled
for secure
operations.
The simple simulations
here demonstrate
the
basic ideas of the concept. The ECS is integral to providing
915
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faster response needed to damp dynamic
as respond
here
on
to faster
security
rudimentary.
and
There
of the best overall
numbers
instabilities
load fluctuations.
operations
remains
of
much
operations
1997, pp. 104-108.
as well
[10] D.
The ideas presented
such
a system
to be addressed
philosophies
given
Shirmohammadi
Meshed
in terms
IEEE
significant
Distribution
Transactions
[11] CIGRE
Exciting
“Fuel
Edmonton,
[2]
Cell-MTG
Innovation
Proceedings
of
[4]
Evaluation
Watts,
39:1999,
No. 1.
Tomsovic,
“Issues
Systems, Hakone,
S. Li,
K. Tomsovic,
Using
[6]
IEEE
Power
and R.N.
New
Kevin
and
of
IEEE
Working
York:
Plenum
Group
on System
K.
Tomsovic,
university
positions
University,
National
Institute
in
Controls
1997
International
Applications
Resources,”
Technology
Electrical
for
1971,
Systems, Vol.
Hiyama
period
1984, pp.
“Trial
he is an
University.
His
Systems
and
various
power
Energy
Chair
at
Kumamoto
his B. E., M. S., and Ph.D. all in
1980,
respectively.
Kyoto
University,
in
Kumamoto
in 1971, and he has been a professor
of Electrical
of June
Science
1985 through
since
September
1989. During
and was involved with Power System
His current interests include Intelligent
control of photovoltaic
system, and harmonic
analysis in
distribution
systems. He is a senior member of IEEE, and a
Fuzzy
of the
member
System
of SICE of Japan, and Japan Solar Energy Society.
BUS7 I
Bs
d
@S
Bs
BI+S
B7s4
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(--’j)
BUS9
Ldl
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A
Bu
Ld3
Y
I
Bl
BUS8
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●
Ld7
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Ld5
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I
Fig. 1 Test System
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Ld2
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0-7803-6674-3/00/$10.00
0-7803-6672-7/01/$10.00
(C)(C)
2000
2001
IEEE
IEEE
the
1986, he was at
Systems, Seoul, Korea, July 6-10,
Busl
1969,
joined
and Computer
He
Control of Electric Power Systems using fuzzy logic control
scheme and neural network,
measurements
and real time
Reliability
on Intelligent
received
Clarkson University,
Harmonics research.
Use
to
Kung
and the Royal
Currently,
State
applied
from
Engineering
of
University
1999 to 2000, he held the Advanced
Engineering
and
University
Evaluation
Visiting
Cheng
in Japan.
Electrical
Systems,”
National
Intelligent
methodologies
Tech.
and Ph.D.
Seattle, in 1984 and
in Stockholm.
include
Michigan
M.S.
5 MW
7---1,
of
Generation
Engineering.
at Washington
From
Takashi
“Modeling
included
Sun Yet-Sen
systems problems.
University
Meeting,
Distribution
#14.
Conference
to Power
have
of Technology
optimization
Following
Design,
from
Vol.
all
interests
“Stability
Analysis
Methods
of
for Power Systems,” Proceedings
Logic
Forms
& Sons, New York,
and the
of Washington,
respectively,
research
Press,
the B.S.
1982,
in Electrical
1979, pp.436-444.
Reliability
in
1987,
Autonomous
of Distribution
Guide
for
Electric
Power
Indices;
Report p1366, Draft
[9]
3, No. 2,
June 2000.
Power
John Wiley
degrees from University
Professor
and I.R. Homer,
Allan,
New
Wollenberg,
received
Houghton,
Associate
Summer
Apparatus
Tomsovic
University,
210-239.
[8]
and B.F.
Gas
Security
Energy
on Power
Modeling
Draft Report,
and Control,
Proceedings
“Load
PES
the Reliability
Systems,
and
Distributed
IEEE
No. 2, Nov.lDec.
R. Billinton
Networks,”
Vol.
1996.
-1998,
on-line,
Systems,”
Distributed
Transactions
PAS-98,
[7]
Systems,
38.01.10,
Wood
Operation
Japan, July 1998.
Seattle, July 2000.
R.N. Allan, E.N. Dialynas
and Evaluating
News
and T. Hiyama,
the
Class
Reliability
on Intelligent
of
Transmission
and
Residential,
New
GGTN
Power
Power
Functions
A
of
Autonomous
Proceedings
and
“A
for Weakly
BIOGRAPHIES
PE-480-PWRS-O-1
Systems (in press).
NERC,
of the Workshop
Hong,
Method
Meeting,
– An Economics
for commercial,
“Microturbine:
Engines:
Distributed
[5]
most
10 Years”
Summer
et al, “Microturbines
Turbine
K.
- The
in the Next
IEEE-PES
Remote Load Applications;
[EEE Transactions
on Power
J. H.
W.
Flow
on Power
and Storage,
Canada, July 1999, pp. 581-586.
M. W. Davis,
Reliability
[3]
Hybrid
in Power
1999
TF
Generation
[12] A.J.
S. Hamilton,
H.
Power
May 1988, pp. 753 – 762.
of DER units.
REFERENCES
[1]
and
- Compensation-Based
are
I
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50
100
150
200
-1
—
500p-----So
100
150
200
30
100
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200
50
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200
50
100
150
200
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0
50
100
150
1
200
I
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50
100
150
I
200
0
500
200,
[
100
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o
400 e4
200 -
u 200 ii?
01
o
CJ
I
so
100
1s0
-o
200
1000 -“”
Q
1000 -
e
01
400;
I
50
100
150
of
200
1
400:
I
-400 I
iii
o
50
100
150
200
I
lima+)
Fig. 3 Response to load change with ECS
Fig. 2 Response to load change with no ECS
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2000
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IEEE
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