The International Conference on Electrical Engineering 2008 �
First�page�Template� No. O-018
Secretariat�uses�only.�Do�not�type�in�this�box.�
� 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.�
� � � 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.�
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.� �
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Second�page�and�after�Template� July 6-10, 2008, OKINAWA, JAPAN Secretariat�uses�only.�Do�not�type�in�this�box.� � 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.� �
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.� �
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Figure�4.�Speed�deviation�controlled�by�governor�
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Figure�1.�Single�line�diagram�of�the�target�system� � P V (k W )
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Figure�5.�Matlab�representation�of�the�Synchronous� generator�and�the�governing�system�(GOV)�
Figure�2.�Total�output�of�the�photovoltaic�generation�units� �
� 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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60 80 100 120 140 160 180 � 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�
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The International ConferenceSecond�page�and�after�Template� on Electrical Engineering 2008
Secretariat�uses�only.�Do�not�type�in�this�box.� � 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.� �
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� �
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Figure�8.�Multi-agent�setting� � The�configuration�of�the�Multi-Agent�system�is�shown�in� Figure�9.� �
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Figure�7.�Speed�deviation�controlled�by�the�ECS-Diesel� coordination�controller�
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� 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.�
� 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.� � �
� 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.�
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Second�page�and�after�Template� July 6-10, 2008, OKINAWA, JAPAN Secretariat�uses�only.�Do�not�type�in�this�box.� � P e c s �(k W )
The�arrow�at�point�(a)�in�Figure�11�indicates�the�time�when� 500 0 the�AGC�control�on�the�ECS�is�activated.� -500 � 0 20 � � � � � � � � 3� � � � � (1)� � � � � � � � 21� � � 0 � 0 20 Where�dω�is�the�speed�deviation�taken�at�the�diesel�generator� 4000 side� and� N� is� the� number� of� the� taken� data.� As� a� result� the� 2000 frequency�of�the�system�is�supposed�to�be�determined�by�the� 0 20 frequency�of�the�diesel�generator�which�is�represented�by�the� 3000 speed�deviation�in�this�paper.� 2000 1000 �
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Figure�12.�Simulation�result�where�only�Governor�is� activated�for�AGC�
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Table�1.�Speed�deviation�under�different�control�action� �
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Figure�10.�Simulation�result�in�case�of�a�step�variable�load� and�without�any�control�action�from�the�ECS�
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� � 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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Figure�11.�Simulation�result�using�the�ECS-Diesel� coordination�controller� �
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The International ConferenceSecond�page�and�after�Template� on Electrical Engineering 2008
Secretariat�uses�only.�Do�not�type�in�this�box.� � [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� isolated�power�systems,”�Generation,�Transmission�and� distribution,� IEE,� Volume� 141,� Issue� 5,� Sep� 1994� pp.491�–�496.� [4]�Sodzawiczny,�G.�and�Sowa,�“Multicriterial�adaptive�load� shedding� algorithm,”� Proceeding� of� International� Conference� on� Electric� Power� Engineering,� Budapest,� 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� Large-Scale� Photovoltaic� Power� Integration� on� electricity�distribution�networks,”�Renewable�Energy�32,� pp.�216-234,�2007.� � 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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