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1�
� Automatic�Generation�Control�of�Islanded�Power�Distribution�System�
with�Dispersed�Power�Sources�
�QUDAIH,�Yaser�and�HIYAMA,�Takashi�
Department�of�Computer�Science�and�Electrical�Engineering�of�Kumamoto�University�
39-1�Kurokami�2-chome�
Kumamoto�860-8555,�Japan�
�Abstract�
�Intended�islanding�of�the�electrical�power�distribution�system�requires�high�techniques�and�big�caution�to�control�the�frequency�
of�the�entire�system,�where�the�upper�electrical�system�that�is�responsible�about�holding�the�frequency,�is�absent.�In�the�past,�load�shedding�technique�has�been�utilized�to�implement�this�goal.�This�paper�comes�after�a�previous�job�of�load�following�
operation�control,�done�and�completed�before�isolating�the�system.�The�well�known�Automatic�Generation�Control�(AGC)�is�
presented�in�this�paper�to�maintain�the�frequency�of�the�islanded�system.�Although�environmental�dependent�renewable�energy�
sources,�such�as�grid-connected�photovoltaic�systems,�are�present�and�spread�within�the�target�system,�the�frequency�can�be�controlled� by� the� technique� used� in� this� paper.� Energy� Capacitor� System� (ECS),� which� has� fast� charging�and� discharging�
capabilities�plays�the�main�role�of�AGC�actively,�compared�with�a�governor�system.�
�Keywords:�Isolated�power�distribution�System,�frequency�control,� �
automatic�generation�control,�energy�capacitor�device,�loads�shedding.�
�
�1�INTRODUCTION�
�It� is� obvious� to� every� researcher� in� the� field� of� electrical�
energy�that�the�huge�interest�and�attention�to�the�distributed�
generations� and� their� impact� on� the� electrical� system,� is�
going�rapidly�due�to�the�reason�of�environmental�concerns.�
However,�this�paper�is�dealing�with�the�performance�of�the�
isolated� power� distribution� systems,� in� the� presence� of�dispersed� power� sources.� Most� of� the� studies� considered�
distribution�system�as�an� interconnected�system,�which�has�
been�discussed� in�a�previous� job�[1].� Few�others�discussed�
about�isolated�or�stand�alone�power�distribution�systems�[2].� ��
In� fact,� interest� in� isolated� power� systems� is� rapidly�
increasing.� In� standalone� systems� the� frequency� is� quite�affected�by�the� unbalanced� situation� between� the� load� and�the� generation,� for� example�when� the� demand� exceeds� the�
generation,�the�frequency�tends�to�be�decreased�or�dropped�
and�conversely,�when�the�generation�exceeds�the�demand�the�
frequency� of� the� system� will� be� increased.� Some� adaptive�
load�shedding�algorithms�have�been�used�and�performed,�in�
order� to� solve� the� problem� of� frequency� deviation� in� the�
isolated�power�systems�[3],�[4].�However�theses�methods�are�
mentioned� here� just� to� be� compared� with� the� proposed�
methodology.� In� this� paper� the� load� shedding� process� has�
been� checked� simply� by� adding� and� isolating� some�of� the�
fixed� load� connected� to� the� system� without� adopting� any�
special�algorithm.� �
�
This� paper� is� studying� the� performance� of� a� completely�isolated� system,� which� contains� photovoltaic� units� as� a�
renewable� energy� or� dispersed� power� source.� The�
unbalanced� generation-demand� situation� caused� by� the�
photovoltaic� units,� which� is� environmentally� dependent�
power�sources,�in�addition�to�the�variable�load,�results�in�a�
disturbance� in� the� frequency� of� the� system.� Energy�Capacitor�System�(ECS)�is�utilized�to�solve�this�problem�via�
the� unique� characteristics� of� this� device,� such� as� fast�
charging� and� discharging� capabilities� [5].� A� coordination�
scheme�between�the�ECS�and�a�diesel�unit� is�used�to�keep�the� charging�and�discharging�level�of�the�ECS� in�a� certain�
desired� level� [6].� Furthermore� the� ECS� control� action� is�
compared� with� the� action� of� governor,� modeled� for� this�purpose�i.e.�to�compare�and�check�the�efficiency�of�the�ECS�in�performing�that�action.� �
�
2�TARGET�SYSTEM�
�
The� target� system� in� this� paper� is� a� ring/loop� distribution�
6.6kv,� 60�Hz� system,�which� is� reconfigured� into� different�
radial� systems� and� same� applications� were� applied� on� all�
reconfigured�cases�that�is�applied�in�some�special�areas,�like�
airports� and� other� isolated� islands.� The� Energy� Capacitor�
System� (ECS),� which� has� fast� charging� and� discharging�
capabilities� plays� the� main� role� of� AGC� actively,� by�
providing� the� generation� and� demand� balance� condition.�
�
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� 2�
Coordination� between� one� of� the� controllable� generation�
units,�which�is�diesel�generator�in�this�case,�and�between�the�ECS,�is�implemented�to�keep�the�ECS�system�in�the�desired�
charging� and� discharging� level.� Multi-Agent� System� and�
computer�networks� are� also�utilized�in� case� the� diesel� unit�
and� the� ECS� are� not�in� the� same�location,� to�complete�the�coordination� process.� In� order� to� take� into� account� many�
other� measures�such�as�economical�aspects� and� flexibility,�
several�locations�and� different�sizes�of�the�ECS� have�been�tested.� The� single� line� diagram� of� the� target� system� is�
illustrated�in�Figure�1.�
�
Photovoltaic� system� is� connected� at� every� node� of� the�described� system� [7],� in� the� form� of� grid� connected�
photovoltaic� system,� of� different� variable� outputs,� to�
represent�a�real�situation.�Figure�2�shows�the�total�output�of�
the�photovoltaic�generation�units�that�have�been�considered�only�at�the�AC�side�for�the�sake�of�simplicity.�The�variation�
of� power� output� from� the� photo� voltaic� units� is� the� main�fluctuation� caused� in� the� entire� system.� Another� changes�
caused� by� a� step� load� variation� is� also� added� to� cause� a�
sudden�increase� in�the�demand,�in�such�a�way� to�show� the�
response� of� the� ECS� and� the� control� efficiency,� Figure� 3�
shows�the�step�load�variation�added�to�the�system.�
�
�Figure�1.�Single�line�diagram�of�the�target�system�
�
0 20 40 60 80 100 120 140 160 1800
1000
2000
3000
P V ( k W
)
�Figure�2.�Total�output�of�the�photovoltaic�generation�units�
�
0 20 40 60 80 100 120 140 160 180
0
500
1000
P l o a d
( k W
)
�Figure�3.�Step�variable�load�
�
3�METHODOLOGIES�
�
Load� frequency� control� (LFC)� or� automatic� generation�
control� (AGC),� which� is� commonly� used� to� control� the�frequency�of�big�systems,�by�regulating�the�power�output�of�
electric�generators� within� a� prescribed�area,� in� response�to�
changes� in� system� frequency,� is� proposed� in� this� paper.�
Multi-Agent�based�AGC�has�been�also�tested�when�the�ECS�and� the� diesel� unit� are� not� in� the� same� location,� by�using�
computer�networks,�to�send�and�receive�information�between�
these�two�controllable�units.�In�this�paper�the�target�system�
and�the�control�strategy�have�been�modeled�and�simulated�in�Matlab/Simulink�environment,�where�the�application�on�the�
frequency�control�has�been�made�according�to�the�following�
scenarios:� � ��
3.1�Governing�system�
�
Governor�of� ideal� characteristics�has� been�modeled�for� the�purpose�of� frequency�control,� to�compare� its�function�with�
the�function�of�the�ECS,�which�has�the�main�mission�in�the�
proposed�methodology.�Figure�4�shows�the�speed�deviation�
when�the�system�is�supported�by�the�governor�attached�to�the�diesel� unit� which� is� deriving� a� synchronous� generator,� as�
shown� in� Figure� 5.�The� graph� shows� the� speed� deviation�which�corresponds� to� the� frequency�of� the� system.� In� this�
case�the�ECS�is�out�of�service.�
�
0 20 40 60 80 100 120 140 160 180-0.1
-0.05
0
0.05
0.1
d w
� ( r a d / s )
time(s) �Figure�4.�Speed�deviation�controlled�by�governor�
�
�
Figure�5.�Matlab�representation�of�the�Synchronous�generator�and�the�governing�system�(GOV)�
�
3.2�ECS�system�
�
Energy� Capacitor� System� in� the� form� of� double� layer�capacitor� is�mostly� located� at�the� same�position�where� the�
controllable� diesel� generating� unit� is� placed.� The� balance�
between�the�generation�and�demand�is�provided�due�to�the�
fast� charging� and� discharging� characteristics� of� the� ECS.�The�coordination�controller� is�shown�in� Figure�6,�where�PI�
controller�is�used�for�the�purpose�of�supporting�the�ECS�that�
has�a�small�size,�and�in�order�to�keep�the�ECS�in�a�specific�
operating�range.�Figure�7�shows�the�simulation�result�when�the� system� is� supported� by� the� ECS� in� the� same� location�
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� 3�
with�the�diesel�unit.�In�the�mentioned�graph�at�point�(a)�the�
AGC�control�on�the�ECS�is�activated.�If�the�ECS�and�the�diesel�unit�are�not�in�the�same�location,�
the� coordination� process� cannot� be� hold� unless� a�
communication� process� is� provided� to� coordinate� between�
the�two�units.�Multi-Agent�system�scheme�has�been�utilized�here�as�explained�below.� � � �
�
�Figure�6.�Coordination�controller�between�the�ECS�and�the�
diesel�unit,�� Where�Et:�is�the�target�stored�energy�of�the�ECS�
� EECS:�is�the�stored�energy,� �
PECS:�is�the�ECS�power�output,� �
and�Pm:�is�the�control�signal�to�the�diesel�unit��
0 20 40 60 80 100 120 140 160 180-0.1
0
0.1
d
w
� ( r a
d
/ s
)
time(s)a
�Figure�7.�Speed�deviation�controlled�by�the�ECS-Diesel�
coordination�controller�
�
3.1�Multi-Agent�based�AGC�
�
It�has�been�noticed�that�the�ECS�can�be�easily�placed�in�the�
same�location�of�the�completely�isolated�power�distribution�system,�but�in�some�cases�such�as�if�the�system�was�already�
connected�to�upper�system�as�in�[1],�so�the�ECS�cannot�be�
moved� to� another� position.� Multi-Agent� system� is� a�
computer� network� consists� of� several� personal� computers�
called� agents� are� responsible� about� sending� and� receiving�
data�among�each�others,�to�perform�the�control�strategy�and�
provide�the�coordination�scheme�between�some�elements�of�
the� system,� namely� the� ECS� and� the� Diesel� Generator,�
regardless� to� the� communication� time� delay� which� is�
neglected�in�this�case.�Those�agents�are�mainly�divided�into�
three�parts:�
� A)�Monitoring�agent�has�the�mission�of�measuring�the�data�required�from�one�part�of�the�system�and�supply�it�through�
the�computer�network�to�the�supervisor�agent.�
� B)� Supervisor� agent� plays� the� mission� of� coordination�
among�the�controllable�devices�in�the�system,�it�is�obviously�
provided�with�the�suitable�algorithm�and�control�strategy�in�
order�to�send�the�required�data�to�the�control�agent.�
�
C)�Control� agent� has� the� mission� of� applying� the� control�signal� via� sending� the� control� signal� to� the� desired�equipment,� which� is� the� diesel� generator� in� this� case� to� �
make� it�acts�according� to�the� control�value,� to�support� the�
Energy�Capacitor�System,�which�is�small�in�size�but�fast�in�
charging�and�discharging.�Analogue�to�digital�convertor�A/D�and� digital� to� analogue� converter� D/A,� including� digital�
signal� processing� board� DSP,� are� used� to� perform� the�
Multi-Agent�based�control�action.�Figure�8�shows�the�setting�of�the�Multi-Agent�in�the�system.�
�
�Figure�8.�Multi-agent�setting�
�
The�configuration�of�the�Multi-Agent�system�is�shown�in�Figure�9.�
�
�Figure�9.�Multi-Agent�system�general�configuration�
Where�DG:�is�the�diesel�generator�
�
4�DETAILED�SIMULATION�RESULT�
�
More� results� obtained� by� digital� simulation� and� following�different� scenarios,� in� addition� to� the� numerical� results�
obtained� by� calculating� the� maximum,� minimum� and� the�
mean�speed�deviation,�as�shown�in�Table�1.�The�index�used�
to�evaluate�the�simulation�result�is�the�mean�speed�deviation,�
calculated� by�Matlab� and� using� equation� 1.� The� efficient�
usage� of� the� ECS� system� to� implement� the� AGC� for� a�
constant�frequency�is�shown�clearly.�Figures�10,�11�and�12,�
illustrate� the� simulation� results� for� defferent� cases,� where�
Pecs�is�the�output�power�of�the�ECS,�Eecs�is�the�stored�energy�
of� the� ECS,� Pdg� is� the� diesel� unit� power,� PV� is� the�photovoltaic�units�total�output�Pload�is�the�step�variable�load�
and�dω�is�the�speed�deviation.� �
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� 4�
The�arrow�at�point�(a)�in�Figure�11�indicates�the�time�when�
the�AGC�control�on�the�ECS�is�activated.��
� � � � � � � � � � � � �
(1)� � � � � � � � � � �
�Where�dω�is�the�speed�deviation�taken�at�the�diesel�generator�
side�and�N� is�the�number�of�the�taken�data.�As�a� result� the�
frequency�of�the�system�is�supposed�to�be�determined�by�the�frequency�of�the�diesel�generator�which�is�represented�by�the�
speed�deviation�in�this�paper.�
�
0 20 40 60 80 100 120 140 160 180-500
0
500
P e c s ( k W
)
0 20 40 60 80 100 120 140 160 1800
1
2
3
E e c s ( k W
h )
0 20 40 60 80 100 120 140 160 180
2000
4000
P d g ( k W
)
0 20 40 60 80 100 120 140 160 1800
1000
2000
3000
P V
( k W
)
0 20 40 60 80 100 120 140 160 180
0
500
1000
P l o a d ( k W
)
0 20 40 60 80 100 120 140 160 180-1
0
1
2
d w� ( r
a d / s )
time(s)
�Figure�10.�Simulation�result�in�case�of�a�step�variable�load�
and�without�any�control�action�from�the�ECS�
�
0 20 40 60 80 100 120 140 160 180-1000
0
1000
P e c s ( k W
)
0 20 40 60 80 100 120 140 160 1800
1
2
3
E e c s ( k W
h )
0 20 40 60 80 100 120 140 160 180
2000
4000
P d g ( k W
)
0 20 40 60 80 100 120 140 160 1800
1000
2000
3000
P V ( k W
)
0 20 40 60 80 100 120 140 160 180
0
500
1000
P l o a d ( k W
)
0 20 40 60 80 100 120 140 160 180-0.1
0
0.1
d w� ( r
a d / s )
time(s)a �Figure�11.�Simulation�result�using�the�ECS-Diesel�
coordination�controller� �
0 20 40 60 80 100 120 140 160 180
-500
0
500
P e c s ( k W
)
0 20 40 60 80 100 120 140 160 1800
1
2
3
E e
c s ( k W
h )
0 20 40 60 80 100 120 140 160 180
2000
4000
P d g ( k W
)
0 20 40 60 80 100 120 140 160 1800
1000
2000
3000
P V ( k W
)
0 20 40 60 80 100 120 140 160 180
0
500
1000
P l o a d ( k W
)
0 20 40 60 80 100 120 140 160 180-0.1
0
0.1
d w� ( r
a d / s )
time(s)
� �Figure�12.�Simulation�result�where�only�Governor�is�
activated�for�AGC��
Table�1.�Speed�deviation�under�different�control�action� �
��
4�CONCLUSION�
�
The�proposed�methodology�of�automatic�generation�control,�by� utilizing� the� Energy� Capacitor� System,� supported� by�a�
diesel� unit,� is� efficient� to� control� the� frequency� of� the�
isolated�system.�Either�the�two�controllable�units�are�in�the�same� location� or� not� the� proposed� methodology� still� the�same�with�the�help�of�Multi-Agent�system.�
�
�
REFERENCES�
�
[1]�Yaser�Qudaih�and�Takashi�Hiyama,�“Reconfiguration�of�
Power� Distribution� System� Using� Multi� Agent� and�
Hierarchical� Based� Load� Following� Operation� with�
Energy� Capacitor� System,”� Proceeding� of� The� 8th�
international�power�engineering�conference�(IPEC2007),�
Singapore,�Dec.�3-7,�2007,�pp.�263-267.�
�
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[2]� T.� Kato,� H� Kanamori,� Y.� Suzuoki� and� T.� Funbashi,� � � �
“Multi-Agent� Based� Control� and� Protection� of� Power�Distribution�System�-Protection�Scheme�with�Simplified�
Information� Utilization-,”� Proceeding� of� the� 13th�
International� Conference� on� Intelligent� Systems�
Application� to� Power� Systems,� Nov.� 6-10,� 2005,� pp.�49-54.� �
[3]�J.G.�Thompson�and�B.�Fox,�“Adaptive�load�shedding�for�
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pp.491�–�496.�
[4]�Sodzawiczny,�G.�and�Sowa,�“Multicriterial�adaptive�load�
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Hungary,�1999,�PP.192.�
[5]� M.� Okamoto,� “A� basic� Study� on� Power� Storage�
Capacitor�Systems”,� Trans.� IEE�of� Japan,�Vol.�115-B,�No.5,�1995.�
[6]�Yaser�Qudaih�and�Takashi�Hiyama,�“Frequency�Control�for� Islanded� Power� Distribution� Systems,”� Proceeding�
of�the�1st�International�Student�Conference�on�Advanced�
Science� and� Technology� (ICAST),� Kumamoto,� Japan,�
March�13-14,�2008,�pp.165-166.�
[7]� Jukka� V.� Paatero� and� Peter� D.� Lund,� “Effects� of�
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�
Biographies� �
Yaser�Qudaih�He�received�his�BSc.�from�
University� of� Engineering� and�Technology� (UET),�Lahore,�Pakistan,�as�
an� electrical� engineer� in� the� year� 1996.�He� received� his� M.Eng.� degree� in�
electrical� engineering� from� Kumamoto�
University,�Japan�in�2008.�Currently�he�is�
a�Ph.D.�student�in�Kumamoto�University,�Japan.�
Hiyama�Takashi�He�received� his� B.�E.,�
M.� S.� and� Ph.� D.� degree� in� electrical�
engineering� from� Kyoto� University� in�
1969,�1971�and�1980,�respectively.�Since�1989,� he� has� been� a� professor� at� the�
Department� of� Computer� Science� and�Electrical� Engineering,� Kumamoto�
University,� Japan.� Currently� he� is� the� Dean� of� Graduate�School� of�Science�and�Technology�of� the�same�university.�
He�is�a�senior�member�of�IEEE,�a�member�of�IEE�of�Japan,�
and�Japan�Solar�Energy�Society.�
�
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