M.H. l)lianu I'ra kasli
1l.S.Cliand raseklia raiah
Department of High Voltage Eiigineeriiig
Indian Institute of Science
h i g a l o r e - 560 012 , INDIA
eniail. blianu~live.iisc.eriiet.iii
AICISTHAC'I'
Object Orieiitecl Metliotlology (OOM) lins rcldctl a IICIV clinreesioti for tire
represetitation, madelirig rntl siinul:ttion of v:irious day-to-clay applicatioIis. 'l'lic brisic
prrrdigin of OOM reflects ~IIC
closc~icssto ivliicli (lie nictliodology rclrtes l o tlic rcal
w o r l d entities. O v e r a I)eriotl of tiiiic, tlie requiretiietit of tletnilecl atitl exact
represoitntioti with no npp-oxiinntioii or rcal world objects tlint reflccts i t s bciitiviornl
pattern is on tile rise. 'I'liis has reseltccl ia tlie terminology of 'Coiiiplex Objccts' in
systeni sinidation. hi AC-MTDC systciii bas several ialcrrelatccll iiitcrcoiincctcci
compoiieiits aircl pose SI complex picture. 0l)jectifying such system will render tlic systeiii
design/ analysis/ identification/ perforeisiicc cvalualion and control, niore easy aiiti iicll)
in better unclerstaecliiig o f (lie systeir i i i its aitirety. 111 (Inis paper, n full relwesctitntion
of the various I)C syste~iis sub coliil)oticiits arc risctl fur clcvclupiiig ciassc~ of
compoiients. Detrilecl representntioti nlorig with tlic various a1tributes aiicl nictliotlologics
associatecl with each o f these conipoiients a r c rc~)resentetl.The case study underla kcii in
this I)aper i s a Four 'I'crniianl AUM'I'DC systeiii with a l l its ternii1i:il c o i i i ~ ~ o i i e ~'1'11~
i~s.
paper liigliligiits the various aclvniilagcs tlic OORl teclinique offers f o r I'o~vcr Systcn~
Modeliiig. This nolatiori is of iiiiinciisc Iicll) esl)ecially (luring tlic systeiii tlcsigii st;~pc
wherciii the tuning of various systciii con~l~onents
can be acliicvcrl without unrlcrgoiiig
tlie rigor of the conventioaal niethocls.
KEY W O W S :
Object Oriented Mctliocls (OOM), Objcct Oriciitecl 1)esign (OOD), Objcct Or-iciitctl
Analysis (OOA), IlVDC l'raasmission Systeni, Systeni Simulation.
i
The basic building block of an OOM is ai1 Object. An
Object represents a set of data aiid its associated
metliodologylf~ioctioiiality bundled into a single unit. 111
tlie coiiveiitional paradigm, the data atid tlie fuiictioiis
associated with the tlierii (i.e., with data) are separated
and are dilTereiit entities. Ai1 Object is coiiipletc by itself
and embeds both the data structure aiid the associated
methods. Ail Object Oriented Approach is cliaracterized
by tlie following important properties
1.1 Class Itlcntity :Classes are collectioiis of objects tliat
has coininoii features viz., the iiietliods and data
stnictures. Objects are instaiitiatioil of these classes.
Typically, tlie identificatioii of the classes are based oil the
real world eiitities aiid coiiccpts of the application of
doinaiii. 'l'lie classes/objects conitiiuiiicate with each other
by inessagc passing paradigins. Dy this data duplication is
avoided and cllanges witliti the objects are not propagated
to other objccts. The class lias the following properties :
Captures the iiistaiice-of rclntionsliip between at1
iiistaiice aiitl tlic class to wliicli it belongs to.
Aggregates the collection of related objects.
0-7803-3 115-X/96$5.000 1996 IEEE.
Eiiliances tlie iiotioii of seinniitic integrity.
Factors out the specification of attributes and nietliods
rroin all iiistaiices or tlie class into a singlc obicct.
wliicli results in savitig of spiices.
The attribute of the classes aiid the classes itself caii be
classified into tliree groups depending 011 the scol)ing
required for the agplicatiou
Private AttributedClasses
I1ublic AltributeslClasses
Protected AttriboteslClnsses
I t is these features h a t enables to define clnsscs of
coinpoiients each with its own specific properties
.
1.2 Encapsulation : The property of encapsiilalioti aiid
tlie iiifonnatioii hiding allows tlie data striicture niitl tlie
iinpleineiitatioii details of the ob,icct to bc Iritltlcn horii
other objects/utilities in the systeni. To capture tlic ciinenl
state of the object, iiiessagc is passed oiilo tlie ob,iects
whose inetliod oil execrltion retrieves the itifimiiation
This propeay of object lias incidc OOM a very attractive
proposition for tlie power systeiii applications wlicreitl the
utilities are cross connccted.
97
1.3 Inheritrace : Iitheritarice of classes lets to propagate
the features of tlie classes not only to the objects
beloiigiiig to same classes but also from other classes.
Tliis feature teniied as Multiple Inheritance Also the
inherited properties can be overridden, new feattires can
be added, modified or appcttded, so that new classes can
be evolved.
1.4 Polymorpliism : I'olyinorpliic property refers to thc
ability of wing the salite expression to denote different
operations Polytnorpliism is generally implemented by
wlint is tcmied ns Dynninic Dinding BRnicnlly inl~crilance
is a special kitid of polyrnorpliisrn tltat characterizes an
object oriented system.
2. MERITS OF OOM
The above mentioned prolxriics (I,I - I .4) provide thc
following advantages over the conventional structured
typed iiotatioii
The Object Oriented Architecture's are Decentralized
and lteiice it is possible to support the needs of the
applications tliat create and manage objects with ol).iect
oriented semantics.
With (lie definition or classes and inheritance
concepts, it is possible to reuse code, thereby avoiding
airy replication of code
* With Classificatioii being part of tlie system, the
class structuring provides two basic relationsliips :
Iihcritai\cc
Relatioiisliip
aiid
Clienl-Scrvet
Relatioiisliip These relatiolisliips in tun1 build several
seinaiiticalty rich notions to tlie pliilosopliy of object
bidding l'liis being : is-a, behaves-like, implements,
conibirics, nses, nceds, Iias-a. consists-of rclationsllips.
Appropriate for desigrrirrg objects whose coinplexity
is Iiigh in ternis cost or developmelit,inaititenaiice. etc.
The basic building blocks being Object, the metliods
sild attributes are manipulated from tlie requirelnent
phase down to implernetitatioli stage with no shin in the
paradigin i.e., tlre OBJECT.
3. OUJEC:?. OHIEN'I'ED ANALYSIS & DESIGN
hlEl'lIOI~OLOGY
Analysis iii general is the process of decotnposition of
problems into their compoliellt parts i.e., a process of
specification of user reqiiirellietit and system stnicture and
fiinction indepclidetltly of the nienns of implenieritation or
physical decoiiipositioir of modules or components.
Analysis focuses on 'WHAT a system is to do and
ernbodies the nlle of traceability, 'WHY', wliicli justifies
tlie existence of given result by tying it back to the stated
goals mid objectives.
0 1 1 the otlier hand, Design in general is an
arcliitectural modeling tlint adds details, precision and
impleinecItntioli dependent feattires to the analysis model.
Designs inclride both Pliysical Design i.e., provides
rigorous specification of ilic iiilcrhcc provided by a sct of
object types and Logical Design that merges with Ob.iect
Orientctl Airalysis
Abstract User Reqdreineiit,
Identify Key Domain Ob-iects.
Assembly of those objects iiilo stnicture of a fonn tliat
will support physical design
I n this paper SOMA, a Semantically rich Method for
Object Orierited Analysis is adopted for the case itrider
study. The main reasoii for the choice of tliis nietliodology
is tiial it incorporates all fentitres of CoadlYoiirdoii (its
simplicity). confirms with Clieii's ER triodelitig cotivetitioli
and siipports all strrictiires i.e., Clnssification,
Composition wid Associnlioii. In ntlditioii, this
methodology supports Rules, wliicli eiiliances tlic
Seiiiaiific richness of the aiialysis model. Also it sq)ports
FUZZY OBJECTS aiid INHERITANCE.
Following are tlie major steps involved i n h e analysis
methodology,
Identify Layers
1dentify Objects
Iderttify Strirctrircs
Define Data Semanticsmid
Associatioiis
Add attributes to 0l)jccts
Add Operatioris to Objects
Add Declarative Seniaiitics of tlie
Obiects
Each of 'these steps with a typical case sttidy is dealt iii
detail iii the following sectioris
3.2 Object Orientrtl Drsign (0)
: Sevcial Object
Design teclntiqim are available viz., Boocl1'86 161,
GOOD 171, HOOD [SI,OOSD (91. JSD & OOJSDllO]
and BoocliP I [ I IJ l'lie nietliotlology adopted iii Illis
paper for tlic object based dcsigii is based on BoocIi'9I
design criteria, wliicli caii be classified irlto following
.
steps
IDENTIFY CLASSES
& INSTANCES
- risrially done with
by eitficr Data Flow Diagrams (DFD)[I2( and/or the
textual analysis[ 1-71 on the specification of the network
wider study. From tlie DFD, objects are idcdfied by
looking for both concrete objects aiicl abstract ob;ec(s
the probleni space, objects will be foollrid rrotrt tlie
bubbles and data stores in the DFD. Metliods are
obtained from the process bubbles 0 1 1 tile contrary, ill
textual analysis the ob.iects, its tilethods and allribrites
are identified by identifying tlre graliiriiar of the
specification provided. lablc I identifies p n ~ i s of
speech that is associated with
v;irious tiiotlet
compoiieiitsof tlie object terminology.
iti
Ports o f Speech
P r o m r r Noun
Tobls
g . 0
I
M o d e l Cmmponant
.
: P o r t r o f Speech utlllrsd f o r O D D
devrlopmsnt
3. t Object Oriented Analysis (OOA) : Several Object
Oriented Analysis tecliiiiqcies Sltlaer/Mellor OOSA [ I ] ,
CoadYoiirdoli 121131, Rambariglt [4], SOMA(5] and
several others are proposed and difiereiit tertniIioloLy are
introduced, liowever the underlying priiiciplcs of tlicsc
tcclniiqiies tltat coiistitiilc a OOA principles cait bc
sriinmnrized as follows
98
ESTAADLISfiMENT OF 71fE ViSlUlLtTV O r E A U l OUJECT
111 tIirs step, the
deliiirtroris of the seritariticF of the classes are rderitrlicd
aiid their relatioiislnp bctweeii tltcln IS IdcnilLcd
IN REIATION TO OTHFR Of3JECT.S
E S ~ ' A B L T~ ISEI IINTERFACE OF EAClt OBJECT A N D T H E
HANDLING: Rasically tliis step involves in
EXCEPTION
the establislinient of the interface that each class sliould
have with its associated classes. By doing this step, it is
possible to have proper security to tlie various classes.
Tliis is done by defining the classes and its attributes in
any of tlie following categories
i ) PUBLIC
ii) PRIVATE
iii) PROTECTED
lMPLEMENf AND TEST OOJECTS
: linpletnent tlie
design R S R prototype. Test the system for cohesion end
consistency. Redefine the classes, instances(Objects),
Semantics and structures
learnt.
011
the basis of wliat Iias been
Object SOURCE
Object FILTER
Object SllUNT COhlPENSATION
Object LOAD
The DC systeiii Layer (caii be treated as DC Bus) 011 the
otlier hand embeds
Object CONVERTER TRANSFORMERS
Object CONVERTER
Object DC LINE
Fig. 2.0 represents the Layers identified along witli tlie
embedded objects and IMPLEMENTED-RY links. Here
the tcnii Class & Object is
used intercliiltigeably,
however the classical dehiitioti of an Objcct beitig a11
instantiation of the Class is niaintainetl ill its
itnplernentation and otlietwise.
4. AN ORJECT RASED AC-MTDC SYSTEM
l'lie prototype system under study is a Four Terminal DC
System with rcpresentation of tenninal coniponents.
Fig. I .O represents the system wider study. I n tliis paper,
a Novel Modular Converter Modeling Approacli 1141 is
used for representing tlie thyristor and its triggering
sclienie. The network is litrtlier analyzed in [ 151 by using
digital sinnilation tecliniques. The algoritlini used for
solving the systeni equations is Modified Euler's nietliod
and Fourtli Order Ruiige Kutta procedure. l'lie same
analysis and dcsign iiietliodology are used for developing
tlie object notalioil for the systeni . A step-by-step
procedure involved in tlie devclopinent is sliown This
applicatioii can be extended to any kind of electrical
network
C">
-
1c s".l.m
F10.2.0
8
J
L""..
L A V E R S I d r n l l f l r d fer U T D C
Svdrm
4.1.2 Structure lcletitificntiati : Stntcture ldetitificatioli
can be classified as
Usage Struclurc
Classificatioti Structurc
Composition Structure
Association Structure
.
.
Usage Structure : Tliis structure records the
message passing topology of the systeni. By building the
usage structure, it is possible to reduce tlie coniplexity of
the structure. The Beliavioral model of the objects and
their interaction will be tlie oiitconie of building a Usage
structure.
Fig.3.0 rellects the usage structure or tlie interlinks of
various objects of tlic system tinder considcration Tile
Fig.3.0 sliown is for a typical single AC and DC systeni
interface. The same principle is extended for tlie MTDC
system.
4.1.2.1
1
F
L
C
-
DC
euj
FILTERS.
- LOCAL LOAD
- CAPACITOR.
Fig. 1.0 ! A typlcal MTOC r y a t e m
4.1.1 Layer Identification : Is a nietliodology by wliicli a
given problem domain is decomposed. Tliis is
evolutionnty slcp wliereiii clianges can be made as the
aiialysis step is perfomled. Tlie Layers exist at the top o f
composition stnictures and are genuine objects theinselves
,TrFg=Hz'
in their own way . 'l'lie Layers have metliods itnpleiiietited
by inctliods of etiibeddcd objects tliat form a Layer, by
what are tenned as IMPLEMENTED-BY links Layers in
general receive and send messages and on the receipt
delegate responsibilities to objects tliat they eticapsulate.
Also Layers resolves the polyniorpliic conflicts that niiglit
exist in the embedded objects.
For tlie ctirrent application, Two Layet s are identified,
one each representing an AC system and a DC systeni.
Tlie AC system Layer or tlie AC system Wrapper Object
(can be treated as AC Bus) embeds the following objects
*= e".
S0U.I
4.1 OUJECI' ORIEN'I'EI) ANALYSIS (OOA)
CC.""v(l.
Conr..l.r
T.o".,.r"...
oc
CI...I.O
I
U.UIOK
.TlUCrUlt
-1
lk.
YrDC ...lam
Ll".
CrmCrnrml.
4.1.2.2 Classificrtior Structure : Tlie classification
stnicture records tlie several underlyitig seninntics of [lie
typical class hierarchies that are logical oritconic of tlie
instantiation of' tlie classes. I'lie attributes of classification
striictrire intist contain the spccial attributes : A Kind Or
(AKO) : attribute and MEh1RER:attribritc. Miiltiple
lnlieritatice and Dis.iunctive lnlieritatice can be reflected in
the classification structure. Otlier relations [lint can be
reflected are
EIO or Exclusive Optional : indicate i1i:it each
sobclass's intersection witli tlie otlier siibclass is cnipty
I 1 0 or Incltisive Optional : indicate the subclass inay
overlap
Optional : indicate tliat list is tiot exclusive. tlicre rnay
be iiiore as yet identifictl sitbclasscs.
0
99
Matidaloty : itidicafe tliat a tnetnberof tlie super class
must be atleast one of the subclasses.
All AKO relatioiisliips are Many-to-One association. Fig.
4.0 represents tlie classification structure of tlie typical
Filter Class along with its associations.
F10.4.0
9
CLASSIFICATION S T R U C T U R E o f tho Clo..
4.1.5 Addition of Methods : The MetIioddOlxmtiotis
goveni the beliavior of tlie object and its ititeractioli
(Message Passing) with other objects. The Methods are
identified by STDs and DFDs of the system From the
DFDs, the process bubbles correspond to tlie methods of
the objects. Some of tlie typical methods associated with
the Class Converter if sliowii in Fig. 7.0.
Fill-r
4.1.2.3 Coniposition Structure : must contain A Part Of
(AP0):attribute acid Pnrts: attribute. These attributes are
used as tlie navigational tools. The composition links can
be interpreted at both Class and Object level. Like
classificatioii stnictiire, relatioiis WO, 110, 0 aiid M can
be used but parts do iiot ovcrlnp.
Fig. 5.0 represents tlie composition structure for tlie
Class Filter. Likewise all tlie composition structure for all
the other classes were developed
4.1.6 Addition of I h t r Seninntics to the Objects 1 I h t n
Semantics to the Objects is reflected by iiicorporntirig
RULES to the objects. A Rule Window interfacc providcd
with each of the objects enables to incorporate tlie
associated rules to the object. Rules aid in disambiguating
the Multiple lnlieritaiice Conflicts and also define the
priority for tlie objects. Like attributes aiid methods, rules
may be iiiherited aiid overridden, witti local variation
possible. Decision Tree is used to describe a complex set
of rules. In the present study, siiiiple assertions are added
to the Class PI Controller. The Class Converter iii tiirii
inherits these rules from the Class PI Controller.
4.2 OBJECT ORIENTED DESIGN (001))
is structural relatioiisliip
other tliaii Usage, Classification and Coinpositioii. OMT
is used for identified coinposition structure and
association structures
4.1.3 Object Identification : Several methodologies
viz., Coad/Yourdoii, Slilear/Meller. Objectory Case Use
(51. State Traiisitioii Models (STD) are used for tlie object
identification. Fig. 6.0 sliows Data Flow Diagram (DFD)
froin wliicli objects are inferred froin the bubbles and data
stores.
4.1.2.4 Association Structure
4.2.1 Identification of Classes nntl Instances : This step
in design overlaps with the analysis nietliods, it i s tliis
advantage tliat makes tlic OOD iiictliods attractive for
varied applications. lliis step acts as a iiieasrire for
devolving the classificatioiiof' the problciii doiiisiii fiiillicr.
The DFDs developed are used for object idciitificatioii.
For tlie current application, followitig classes are
developed.
Fig.8.0 reflects the class liierarcliy developcd for the
current study. Class Converter inlierits its properties froiii
the_Class
Base
,_-_..-___________
___
_ Converter, Class Conventional Controller
r.--* -___
I
and froin the Class Intelligent Controller, The
iinpleinentattori IS done such Illit one ol tlie cotitroller IS
instantiated for a given converter.
~
T
FIg.PI.0
4.1.4 Adtlitioii of Attrilwte to Objects : Froin the
various stnictures identified, AK0:attribute aiid
Partattribute (List-Attributes) fonn tlie attribute of the
object under coiisideratioii. Also AlOattribute and
Meniber:attribute also fonn tlie attributes of the object.
Attributes in general are
Pure Attributes - Defiiied (ADTs) or
Pritnitive
Ones.
Associatioii Attribute
Typical attribute list along with tlie simulation parameters
associated with tlie converter is sliowii in Fig. 7.0,tliese
attributes are identified fioai both stnictures and DFDs
100
: Clo..
HI-rorshy
I
for Conv-rt-r
w l l h Conlroll-r.
4.2.2 Estnhlishment of the visil)ility of tlie Objects :
All tlie classes developed for tlie ctirreiit applicntioii was
declared global, however cettaiii attributes of' clnsses were
declared as private nieinbers. Soine attribiitcs were
declared as protected members i n order access tlie values
down the class Iiierarcliy. Tliis step offers security for
object management and is usefill for interlinked utilities.
4.2.3 Establishment of tlir interface for each of the
Object & Exception Ilantlling : A siiiiple filc hnsetl
iiiterfnce for liaiidliiig bot11 dyiiaiiiic nntl constant
parameters of the iietwork was provided. The Overloaded
coiistnictor inclhods provided for each of the classes
Further eiiliaiiced the iii(erface part for each of (lie classes.
Exceptioti
Hatidling iiicluded
it1
the
curretit
impleiiientation is provided by staiidard C++ features viz.,
throw, catch arid try.
[7] SElDWlTZ & STARK, ' (ieneral Ohject Orierttcd
L)Eveloptrrctif, Sonware Eiigiiieering Lellers, 86-002,
1986.
(81
P.ROBINSON, '()hJCCt
~)rk?lflCd / k W j y ' ,
Loiidon:Cliapinaii and Hall.
[9] WASSEMAN,
PlRCllER,et.al, ' 7he Olyc!c/ Oriented
Strtrcttrred lksigii', IEEE Coiiipolcr, pp 50-62, March
1990.
[ 1O)M.A.JACKSON, 'Sy.wnr I)cvc/opinctrt', Eiiglewood
Cliffs NJ,Prentice Hall, 1983.
[ 1 1 J GRADY BOOCH, 'Ohpct Orierited Ik*sigii with
Applications', CA, Beiiajtiiiii Cuiiiiniiigs, 199 1 .
[ 12) EDWARD
YOURDON, 'Modern Slrucluretl Aita~jtris',
Yoitrdoii Press, Englewood Cliffs, NJ, 1989
[ 1 3] R.J.ARBoIT, ' P r o ~ r m tI)e.vigii h.v hformtd l~ngli.vli
Ilescriplions', Coininuiiication of ACM, 26( 1 ), 882-894,
1983.
[ 14) M.MURGESFI
M UDALIAR
&
H.S.CHANDRASEKHARAIAtl,'I)ylla!nic /Jgila/ Siniiilatro~r
of H V I X .ryslcms t i s r r r ~ a Noi~cl Modtilnr Converter
Model', IEEE Trans. 011 PAS, Vol. No.10, OCI 1985, pp
2852-2856.
1S~PREMILAMANOHAR,H.S.ctlANDRASEKHARAIAH,
'ArtiJcial Conimutairorl ,fiw rnrvrsinii into a weak A('
system in Mulliternlinal Hb'IX' systeni,Electric Power
System Research, Vol. 19, No.2, pp. 95-104, 1990.
15,
,
.
.
,
,
5.0 CONCLUSIONS
An Object iiotatioii is developed
iii this paper for the
siinulatioii of Four Tentiinnl MTDC system along with the
tcniiiiial components. Ai1 Objecl notatiori offers a
mechanism that brings tlie model closer to its real world
entity. Tlie data hiding and data abstraction that fonns the
lieart of object tiotatioa, offers a secure environment
especially for cross-linked utilities. Also the network
connectivity could be inferred by tiavigatirig the class
hierarchies and class litiks. This notation fiirther aids tlie
data hniidliiig mecliaiiism i n real time that is ciirretitly
tinder investigation.
I
n
-I
6.0 REFERENCES
[ I ] S.SHLAER & S.J.MELLOR
, 'Object Oricrited Sy.slertrs
Analysis - Modeling the world in data', Englewood Cliffs,
NJ:Yoiirdoii Press, 1988.
[2] P.COAO & E.YOURDON,
'Ol.+x/ Oriented Analysis'
2nd Edition, Eiiglewood Clifls, NJ, Yordoli PresdPreatice
Hall, 1991.
[3J P.Coad & E.Yourdoii, 'Olyecl Orienled Aiialy.sis',
Englewood Cliffs, NJ, Yourdon Press/Prentice Hall,l991.
[4] J. Rambaugli, 'Ohjcct Oricri/ed Modeling arid l)esign',
Prentice Hall, Eiiglewood Cliffs, 1991.
[ 5 ] I.M.Grahaiii, 'Migrating to Ohject techtrolo$p',
Wokingliain, Addison-Wesley, 1994.
[6] GRADYBOOCI I , 'Ohjec/ Oriented lleveiopnrent', IEEE
Trans. on Sonware Eiigitieering, Vol SE-l2(2), 21 I22 I , I 986.
101