Indonesian J
ournal of Ele
c
trical Engin
eering and
Computer Sci
e
nce
Vol. 2, No. 3,
Jun
e
201
6, pp. 510 ~ 52
1
DOI: 10.115
9
1
/ijeecs.v2.i3.pp51
0-5
2
1
510
Re
cei
v
ed Fe
brua
ry 1, 201
6; Revi
se
d Ap
ril 11, 201
6; Acce
pted April 27, 2016
Analysis of Distributed Power Flow Controller in Power
System Network for Improving Power Flow Control
Kuldeep Saini*
1
, Aakash
Saxena
2
, MR Farooqi
3
1,2
S
w
ami Kes
h
w
a
n
and Institut
e of
T
e
chnol
og
y
Man
a
g
e
ment
& G
r
amothan, Jaip
ur, India
3
Compuc
om Institute of
T
e
chnol
og
y a
nd Ma
nag
ement, Jai
pur, India
*Corres
p
o
ndi
n
g
author, e-ma
i
l
: kulde
e
p
eevitj
a
ip
ur@gm
a
il.c
o
m
A
b
st
r
a
ct
In this pap
er, a new
pow
er flow
controllin
g d
e
vice
ca
lle
d di
stributed p
o
w
e
r flow
controlle
r (DPFC)
is pres
ente
d
th
at offers the s
a
me co
ntrol c
a
pab
ility
as t
he
unifi
ed p
o
w
e
r-flow
control
l
er (
U
PFC) but w
i
th
muc
h
low
e
r co
st and hi
gh rel
i
abil
i
ty. T
he DPF
C
eli
m
in
ates the co
mmo
n
D
C
link w
i
thin th
e UPF
C
, to enabl
e
the in
de
pe
nde
nt op
eratio
n of
the sh
unt a
nd t
he ser
i
es c
onv
erter. T
he D-F
A
CT
S conce
p
t
is e
m
p
l
oye
d
to
th
e
series c
onv
erter to
incre
a
se
the re
lia
bil
i
ty. Multipl
e
low
-ra
ting s
i
ng
le-p
ha
se co
nverters
repl
ace th
e
hi
gh
-
rating thre
e-p
h
a
se seri
es con
v
erter, w
h
ich signific
ant
ly red
u
c
es the cost and incr
eases t
he reli
ab
ility. T
h
e
active p
o
w
e
r that is exc
han
g
ed thro
ug
h the
common D
C
li
nk in th
e UPF
C
is now
trans
ferred thro
ug
h
the
transmissio
n
li
ne at the 3rd
harmonic fre
que
ncy. T
he DPF
C
is mod
e
le
d in a rotating d
q
-frame. T
h
e
mo
de
lin
g an
d
ana
lysis of DP
F
C
in a tw
o area tw
o bus
inte
rconn
ected sys
tem is d
o
n
e
in
MAT
L
AB/Simul
i
n
k
envir
on
me
nt a
nd c
o
mpar
iso
n
betw
een
the
DPF
C
a
nd
UP
F
C
consi
der
ing
the
pow
er fl
o
w
and c
o
st ar
e
als
o
show
n.
Ke
y
w
ords
: flexible A
C
trans
m
i
ss
ion system
, unified power fl
ow controller, distribut
ed FACTS, distributed
pow
er flow
controller, pow
er-tr
ans
missi
on co
ntrol
Copy
right
©
2016 In
stitu
t
e o
f
Ad
van
ced
En
g
i
n
eerin
g and
Scien
ce. All
rig
h
ts reser
ve
d
.
1. Introduc
tion
No
wad
a
ys th
e po
we
r
syst
em b
e
come
s
very complex
due
to th
e in
cre
a
si
ng
load
dem
an
d
of the ele
c
tri
c
ity and the ag
ing of the n
e
tworks. Th
e
r
e
is a g
r
eat
de
sire to
control
the po
wer flo
w
in the tran
sm
issi
on li
nes
with fa
st an
d
relia
bl
y
[
1
]
.
Flex
ible A
C
t
r
an
smi
ssi
on
sy
st
em
(FA
C
TS
)
controlle
rs [2] ba
sed
on
p
o
w
er el
ectroni
c
conve
r
te
rs
offer
comp
etitive sol
u
tion
s t
o
today
s
power
system
s in te
rms
of increa
sed p
o
wer fl
ow tr
a
n
sfe
r
capability and
enha
nced co
ntrollability, can
be use
d
for power flow
control.
The UPFC cu
rrentl
y
shown in F
i
gure 1 i
s
the most versa
t
ile
FACTS devi
c
e
whi
c
h
ca
n simulta
neo
usly contro
l
all the pa
ra
meters of th
e system: t
he
transmissio
n angle, bu
s vo
ltage and the
impeda
nce of the line [3].
Figure 1. Simplified diag
ram of UPFC [
4
]
The UPF
C
consi
s
ts
of
a
Static
Synch
r
onou
s Com
p
ensator
(STA
TCOM
) and
a
Static
Synchrono
us Series Com
pen
sator (SS
S
C), whi
c
h a
r
e co
uple
d throu
gh a co
mmon dc lin
k to
allow
bi-dire
c
tional flow of
active p
o
we
r bet
wee
n
th
e two
co
nverters [4]. T
he
seri
es converter
inject
s a volta
ge in
se
ries
with the
syste
m
volt
age through
a serie
s
tran
sform
e
r.
The p
o
we
r flo
w
throug
h the li
ne ca
n be re
gulated by
co
ntrolling vo
lta
ge mag
n
itude
and angl
e of
seri
es inj
e
ct
ed
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ISSN: 25
02-4
752
IJEECS
Vol.
2, No. 3, Jun
e
2016 : 510
– 521
511
voltage [5].
The inj
e
cte
d
voltage
and
line
cu
rrent
determine
the a
c
tive a
n
d
re
active
p
o
we
r
injecte
d
by
the se
rie
s
co
nverter. The
main
fu
nctio
n
of the
shunt
co
nverte
r
(S
TATCOM
) i
s
to
supply or absorb the active power dem
and by t
he seri
es converter (SSSC
). The shunt converter
controls the
voltage of th
e DC
ca
pa
citor by
ab
so
rbi
ng o
r
sup
p
lying a
c
tive p
o
w
er fro
m
the
grid
[6]. The shun
t converte
r also ha
s a ca
p
ability of independ
ently su
pplying or ab
sorbing rea
c
tive
power t
o
reg
u
late the
bu
s voltage
of th
e g
r
id. Al
thou
gh
UPFC hav
e
supe
rio
r
p
o
w
er flo
w
cont
rol
capabilities but it is not widely
used due to the following reasons
[7]: i) Converter compl
e
xity and
high voltag
e
and
cu
rre
nt ratings of co
mpone
nts i
n
cre
a
se the
cost of
UPF
C
; ii) Th
e volta
g
e
isolatio
n of seri
es a
nd shunt conve
r
t
e
rs
r
equi
re
s 3-pha
se hig
h
-voltage tra
n
sformers which
further increase the
co
st
; iii) Due to the
comm
on dc lin
k i
n
terconnection a failure
at one
conve
r
ter will
cau
s
e
the wh
ole
syst
e
m
shut down. In that case to
achi
eve the required reliab
ility
addition
al co
mpone
nts a
r
e
neede
d, whi
c
h ag
ain en
h
ance the co
st
.
To overcom
e
the above di
scus
se
d prob
lems a
ne
w con
c
e
p
t of distribute
d FA
CTS (D-
FACTS) i
s
p
r
opo
sed
by Deepa
k
Divan
[8]. The co
nc
ept of D-FACTS is to u
s
e
multiple lo
w rated
singl
e-p
h
a
s
e seri
es
converters
i
n
ste
ad of
the
la
rge power rated
three
-
p
h
a
s
e serie
s
conve
r
te
r
that attache
d
to the existing po
we
r lin
e and
can
chang
e
the im
peda
nce of the line
so a
s
to
control the p
o
we
r flow. T
h
is con
c
ept
not only re
d
u
ce
s t
he t
o
t
a
l co
st
but
a
l
so in
cre
a
s
e
t
he
reliability of the series converte
rs. Currently, the Dist
ributed Stat
ic Series
Com
p
ensator (DSS
C)
s
h
ow
n
in
F
i
gu
r
e
2
h
a
s
b
een
p
r
es
e
n
t
ed
as
a
me
mbe
r
of D
-
F
A
C
T
S de
vic
e
s
.
Figure 2. Schematic
circ
uit of a DSSC module [9]
The DSSC i
s
a distributed SSSC, which is m
ade up of large number of a small rated
singl
e ph
ase
inverter (1
0~20
kW),
a co
mmuni
cation
link and a sin
g
le
turn
tran
sformer
(ST
T
) [9].
The
DSSC m
odule
s
a
r
e
cl
amped
on tra
n
smi
ssi
on lin
es
so th
at no
extra hig
h
-v
oltage i
s
olati
o
n
and ad
dition
al land i
s
re
quire
d. The
singl
e-tu
rn
transfo
rme
r
u
s
es the tran
smissi
on lin
e as its
se
con
dary
wi
nding
an
d inj
e
cts a
contro
llable volta
g
e
directly into the line. Most of
the volta
g
e
injecte
d
by
a
DSSC
unit i
s
in qu
adrature
with
t
he li
ne
curre
n
t, to e
m
ulate i
ndu
ct
ive or capa
cit
i
ve
impeda
nce. T
he
DSSC i
s
remotely controlled via
wi
rel
e
ss
comm
uni
c
ation
or a P
L
C
(po
w
e
r
lin
e
comm
uni
cati
on) [1
0]. As
compa
r
e
to
UPFC the
DSS
C
i
s
n
o
t a
po
werful
FACT
S device
be
cause
the control
capability of t
he
DSSC i
s
limited, it ca
n only i
n
je
ct
rea
c
tive p
o
wer. In thi
s
pa
per,
DPFC i
s
introdu
ce
d as
a new FA
CTS device,
whi
c
h minim
i
ze
s the limi
t
ations of th
e
conve
n
tional
UPFC. The
DPFC i
s
develope
d by
eliminating the
comm
on dc l
i
nk between
the
shu
n
t and
serie
s
convert
e
rs
and
ha
s the sam
e
capability to simultaneo
u
sly
control all the
para
m
eters o
f
the system at much
lo
we
r co
st and hig
h
er reliability.
This
paper is organiz
e
d as
follows
: In
s
e
c
t
ion II, the DPFC
princ
i
ple is dis
c
u
s
s
ed. In
section III, th
e steady-stat
e
behavio
r of DPFC is analyzed. In section IV, the DPFC cont
rol
scheme i
s
de
veloped. Fina
lly, the modeling of DP
FC, simulatio
n
re
sults un
de
r steady state an
d
step chan
ge
con
d
ition
s
an
d co
st analysi
s
wi
th UPF
C
are p
r
e
s
ente
d in se
ction V.
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IJEECS
ISSN:
2502-4
752
Analysis of DPFC in Powe
r System
Ne
t
w
ork for Im
provin
g Powe
r
Flow Control
(Kuldeep Sai
n
i)
512
2. Rese
arch
Metho
d
2.1.1. DPFC
Principle
The DPF
C
consi
s
ts of sh
unt and se
rie
s
conve
r
ters. The sh
unt co
nverter is
sim
ilar as a
STATCOM, while the seri
es converte
r employ
s the
D-FA
CTS co
nce
p
t. The si
mplified diag
ram
of DPFC with
a two bus
system is
sho
w
n in Figure 3.
Figure 3. Gen
e
rali
zed
DP
F
C
co
nfiguration [11]
In the above
config
uratio
n
there i
s
n
o
comm
on d
c
l
i
nk b
e
twe
en
the sh
unt an
d se
rie
s
conve
r
ters, t
he a
c
tive po
wer can o
n
ly be ex
cha
n
g
e
d is thro
ugh
the tra
n
smi
s
sion li
ne
at third
harm
oni
c fre
quen
cy. The
method of active po
wer exchan
ge in the DPFC is based on
the
prin
ciple
of p
o
we
r the
o
ry
of non
-si
n
u
s
o
i
dal
co
mp
one
nts [11]. Th
e
power th
eory
is
explaine
d
by
Fouri
e
r an
alysis meth
od. It states that, “non-sin
usoid
a
l voltage an
d current can
be expresse
d as
the sum
of sinusoidal
fun
c
tion
s in
different
freq
uen
cie
s
with diff
erent
amplitu
d
es”. Th
e a
c
tive
power defin
e
d
as the mea
n
value of the pr
odu
ct of voltage and
current can b
e
de
fined by:
∞
∅
11
(1)
Whe
r
e
n i
s
the o
r
d
e
r of t
he h
a
rm
oni
c freq
uen
c
y a
nd Ø
n
i
s
th
e
angl
e
betwe
en the
voltage and
curre
n
t of the nth harmoni
c. Eqn. (1) d
e
scrib
e
s that
the active po
wers at different
freque
nci
e
s a
r
e i
s
ol
ated f
r
om e
a
ch oth
e
r
and
the v
o
ltage
or current i
n
o
ne f
r
eque
ncy
ha
s no
influen
ce o
n
the active
power at oth
e
r fre
que
nc
i
e
s. The
3rd
h
a
rmo
n
ic i
s
selecte
d
he
re
to
excha
nge act
i
ve
po
wer, b
e
ca
use
it
can
be easily blo
c
ked by
Y-
∆
transfo
rme
r
s.
The high
-pa
s
s
filter blo
c
ks t
he fund
ament
al freq
uen
cy
comp
one
nts
and m
a
kes
a
clo
s
ed l
oop f
o
r third ha
rm
onic
cur
r
e
n
t
.
2.1.2. Stead
y
-
Sta
t
e Analy
s
is of DPF
C
The
steady-state behavio
r of the DPF
C
is
analy
z
e
d
with a
n
a
s
sumptio
n
tha
t
each
conve
r
ter i
s
repla
c
ed
by contro
lla
ble vo
ltage source
s in se
rie
s
wit
h
imped
an
ce,
and g
e
ne
rat
e
s
the voltages
at two differe
nt freque
nci
e
s [12]. The
DPFC is pl
ace
d
in a two
-
bu
s sy
stem with
the
sen
d
ing e
nd
and the re
cei
v
ing end voltage
s Vs and
Vr, respe
c
tively as sho
w
n i
n
Figure 4.
Figure 4. Simplified rep
r
e
s
entation of
DPFC in two bus
s
y
s
t
em [12]
The tra
n
smission li
ne i
s
repre
s
e
n
ted b
y
an indu
cta
n
ce
L with th
e line
curre
n
t I. The
voltage inje
ct
ed by serie
s
conve
r
ters a
r
eVs
e1
and V
s
e3
at the fu
ndame
n
tal a
nd 3rd ha
rmo
n
ic
freque
nci
e
s,
resp
ectively. The shunt
co
nverter i
s
con
necte
d to the
sen
d
ing
end
bus th
rou
gh t
h
e
indu
ctor L
s
h
and ge
nerate
s
the voltage
Vsh1 and
V
s
h3, an
d the curre
n
t inject
ed by the sh
unt
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ISSN: 25
02-4
752
IJEECS
Vol.
2, No. 3, Jun
e
2016 : 510
– 521
513
conve
r
ter is Ish. Th
e a
c
tive an
d rea
c
tive po
we
r flo
w
s at th
e recei
v
ing en
d a
r
e
Pr an
d Q
r
. T
he
active and re
active po
wer
flow ca
n be e
x
presse
d as f
o
llows:
∙
∗
∙
∗
(2)
Whe
r
e X1 =
ω
1L is the lin
e impeda
nce at the fundam
ental frequ
e
n
c
y. The po
we
r flow witho
u
t
DPFC
c
o
mpens
a
tion (Pr0,
Qr0) is
given
by:
∙
∗
(3)
The po
we
r flow co
ntrol ran
ge of the DP
FC can be ex
pre
s
sed a
s
:
∗
(4)
Whe
r
e P_
rc
a
nd Q_
rc
are the a
c
tive, rea
c
tive po
wer c
o
ntrol ran
ge of
DPFC
, respec
tively.
As
the
voltage at the re
ceiving e
nd and th
e line impe
dan
ce
are fixed, the po
we
r flow co
ntrol
ran
ge of
the DPF
C
i
s
prop
ortio
nal t
o
the
maximu
m voltage
of t
he
se
ries
con
v
erter
wh
ere
t
he p
h
a
s
e
ang
le
of voltage
V*
se1
can
be
rotated ove
r
3
6
0
◦
, thereby
controlling the ac
tive and
reactive power
flow th
roug
h
the tra
n
smi
ssion lin
e. Fro
m
Eqn.
(2) a
nd Eqn.
(3
),
the control
capability of t
h
e
DPFC i
s
give
n by:
|
|
(5)
The control range of the
DPFC i
s
a
circle in t
he
co
mplex PQ-pl
a
ne, the locus
of the power
flow
without the DPFC
comp
ensation f(Pr
0,Qr0
)
is a circle
with rad
i
us |V|2/|X1|
arou
nd its ce
nter
(define
d
by coordi
nate
s
P = 0 an
d Q
=
|V|2/|X1| ).
Each
point of this
circle giv
e
s Pr0 and
Qr0
values of the uncompe
nsat
ed system at the corre
s
po
nding tra
n
smi
ssi
on angl
e
θ
. The bounda
ry
of the attaina
b
le control
ra
nge fo
r Pr a
n
d
Qr i
s
o
b
tain
ed from
a co
mplete rotatio
n
of the volta
g
e
Vse1 with its
maximum ma
gnitude a
s
sh
own in Fig
u
re
5.
Figure 5. DPFC a
c
tive and rea
c
tive po
wer
cont
rol ra
nge with the t
r
an
smi
ssi
on
angle
θ
[13]
The voltage i
n
jecte
d
by the seri
es
conv
erte
r V
s
e1 at
fundame
n
tal frequ
en
cy is g
i
ven by:
∗
(6)
Whe
r
e S_r a
nd S_r0 are the appa
rent
power in
co
mpen
sated n
e
twork an
d apparent po
wer in
uncompe
nsated netwo
rk, resp
ectively. To inject a 36
0
◦
rotatable voltage, an act
i
ve and rea
c
ti
ve
power at the
fundamental
frequen
cy h
a
s to be su
p
p
lied to the serie
s
co
nvert
e
r, althoug
h th
e
rea
c
tive power is lo
cally p
r
ovided to the
serie
s
conve
r
ter an
d the requireme
n
t of active powe
r is
sup
p
lied by the sh
unt con
v
erter at the 3rd ha
rm
o
n
ic frequen
c
y throug
h the tra
n
smi
ssi
on lin
e,
whi
c
h is give
n as:
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IJEECS
ISSN:
2502-4
752
Analysis of DPFC in Powe
r System
Ne
t
w
ork for Im
provin
g Powe
r
Flow Control
(Kuldeep Sai
n
i)
514
|
|
|
||
|
(7)
W
h
er
e
φ
r0
is the
power a
ngle
at the
receivin
g e
n
d o
f
th
e u
n
c
o
mp
e
n
s
a
te
d
sys
te
m, wh
ich is
equal to tan
−
1(Pr0/
Qr0
)
while
φ
r is the
powe
r
angl
e
at the recei
v
ing end of the syste
m
wi
th
D
P
F
C
c
o
mpen
s
a
tion
.
2.1.3. DPFC
Con
t
rol Sch
e
me
The DPF
C
h
a
s thre
e types of controlle
rs: c
entral
co
ntrolle
r, shu
n
t
control an
d
serie
s
control, as
sh
own in Fig
u
re
6.
Figure 6. Block di
agram of
the control of a DPFC [14]
The fun
c
tion of each
controller is d
e
fine
d as given b
e
l
ow:
2.1.3.1. Central Control
The refere
nce sig
nals
gen
erated
by the
centra
l control block a
r
e
sent to both th
e sh
unt
and serie
s
converte
rs
re
motely via PLC commu
ni
cation m
e
tho
d
. Acco
rdin
g
to the system
requi
rem
ents,
the cent
ral
control blo
ck gene
rate
s referen
c
e
sig
nal of voltag
e Vse1
ref for the
seri
es control
blo
c
k an
d
re
feren
c
e
sig
n
a
l
of q
co
mpo
n
ent of th
e
shunt
cu
rre
nt Ish1
qref
for th
e
shu
n
t control block at the fundam
ental freque
ncy.
2.1.3.2. Series Con
t
rol
The se
rie
s
converte
rs
ge
nerate
a
volt
age with co
n
t
rollable
ph
a
s
e angl
e
a
s
well as
magnitud
e
at
fundam
ental
frequ
en
cy, and u
s
e
3rd
h
a
rmo
n
ic f
r
eq
uen
cy co
mpo
n
ents to
ab
sorb
active power
to maintain its DC
cap
a
cit
o
r voltage
s at a consta
nt value [14]. The block diag
ram
of the DPFC serie
s
conv
erter
c
ontrol is sh
own in Figure 7. The seri
es
con
v
erter control
ha
s
different type
s of blo
c
ks:
centra
l
cont
rol,
singl
e-p
h
a
s
e
PLL, dc
cont
rolle
r, 3rd
pa
ss filter,
singl
e
-
pha
se inve
rse dq a
nd P
W
M gen
erato
r
.
To control th
e se
rie
s
conv
erter, Ve
ctor
Control p
r
in
ci
ple
[15] is
used
here.
The
pri
n
cipl
e i
s
to transfo
rm
volta
ges an
d
currents i
n
to
a rotating refere
nce
frame, refe
rred to as the
‘dq-fra
m
e’ a
nd co
nver
t a
c
qua
ntities to dc, u
s
ing
so called ‘Pa
r
k’
s
transfo
rmatio
n’ [16]. Du
e to the u
s
e
of
singl
e-p
h
a
s
e
seri
es converters, a
sin
g
le
-pha
se
Park’
s
transfo
rmatio
n is appli
ed h
e
re.
Figure 7. Block di
agram of
Se
ries Conv
erter Control
[17]
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IJEECS
Vol.
2, No. 3, Jun
e
2016 : 510
– 521
515
The 3rd ha
rmonic
cu
rren
t through the
transmi
ssio
n line is
sel
e
cted a
s
the
rotation
referen
c
e f
r
a
m
e for Park’
s
tran
sform
a
tion b
e
cau
s
e
it can
be
ea
sily me
asu
r
e
d
by the
seri
e
s
conve
r
ter locally without
e
x
tra co
st. As
the li
ne
cu
rre
n
t co
ntain
s
two frequ
en
cy com
p
on
ents,
a
3rd hi
gh pa
ss filter is req
u
ired to extra
c
t t
he third h
a
rmo
n
ic
cu
rrent. The sin
g
l
e-ph
ase Pha
s
e-
Lock-Loo
p
(PLL) [
18] tra
c
k
the mag
n
itud
e an
d p
h
a
s
e
angle
informa
t
ion from
the l
i
ne
curre
n
t an
d
feed it to the singl
e pha
se
inverse Park’
s
tran
sformati
on. The DC serie
s
voltage
and ref
e
re
nce
sign
al of th
e
DC serie
s
vol
t
age a
r
e
take
n a
s
th
e
inp
u
t
of the
DC
control
loop
which
ge
nerates
the req
u
ire
d
control sig
nal
with the help
of PI c
ontroll
er. In additio
n
, by using th
e Internal Mo
del
Control
(IMC) metho
d
[19]
the PI
co
ntroller pa
ramet
e
r i
s
cal
c
ul
ated. Th
e q
co
mpone
n
t of t
h
e
referen
c
e
sig
nal of the
se
ries converte
r at 3
r
d
harmonic freq
ue
ncy is kept a
t
zero d
u
rin
g
the
operation. Th
e above
DC
quantitie
s tog
e
ther
with ph
ase a
ngle
are
transfo
rme
d
back in to AC by
the inverse P
a
rk’
s
tra
n
sfo
r
mation. The refere
n
c
e
sig
n
a
ls at both fre
quen
cy co
mp
onent
s togeth
e
r
gives refe
re
n
c
e si
gnal to serie
s
co
nvert
e
rs
wh
i
c
h is g
enerated by serie
s
co
ntrol
block.
2.1.3.3. Shunt Con
t
rol
The shunt
co
nverter i
s
con
necte
d bet
we
en the g
r
ou
n
d
and th
e ne
utral poi
n
t of the Y-
∆
transfo
rme
r
t
o
inje
ct 3
r
d
harm
oni
c current into
the
line to
sup
p
l
y
active po
wer fo
r the
se
ries
c
onverters
. At the s
a
me time, it maintains
the
capa
ci
tor DC voltag
e of the shun
t converte
r at a
con
s
tant valu
e by abso
r
bi
ng active po
wer from the
grid at the
fundame
n
tal
freque
ncy a
n
d
injectin
g the required rea
c
tive current at the f
undame
n
tal freque
ncy into the grid
[20]. The block
diagram of sh
unt cont
rol is
sho
w
n in Fig
u
re 8.
Figure 8. Block di
agram of
shunt converter cont
rol [17
]
Shunt co
ntrol
block co
mpri
sed
of two co
ntrol loop
s. F
u
ndam
ental freque
ncy cont
rol loop
and
3rd
ha
rm
onic freq
uen
cy control lo
op
. Funda
ment
al
freq
uen
cy
control lo
opm
ainly con
s
ist
s
of
two blo
c
ks: th
e DC
co
ntrol
and current
control. T
he
b
u
s voltage i
s
sele
cted a
s
rotation refe
re
nce
frame fo
r fun
damental
loo
p
. The
refe
re
nce
of the
q
comp
one
n
t of
the
curre
n
t a
nd the
refe
re
nce
sign
al of the d com
pone
nt is gene
rate
d
by the
central cont
rol an
d the DC
co
ntrol blo
c
ks.
The
curre
n
t cont
rol block ge
n
e
rate
s re
quired co
ntrol
si
gnal
s
to the singl
e-p
h
a
s
e
inverse dq frame
with the help
of PI control
l
er. In the 3rd har
m
oni
c frequ
en
cy co
ntrol loop the
third harm
o
nic
curre
n
t ge
nerated by
sh
un
t conve
r
ter is syn
c
hroni
ze
d with
the b
u
s
voltag
e at t
he fun
dame
n
t
al
freque
ncy. A PLL is used to track the b
u
s volt
age fre
quen
cy, and the output sig
nal is multipli
ed
by con
s
tant f
a
ctor 3 to
creat
e de
co
upl
ed do
uble
sy
nch
r
on
ou
s ro
tation refe
ren
c
e frame fo
r
the
3rd
harmoni
c com
pon
ent
[21]. The si
milar
cu
rre
nt
cont
rol
sche
me is
used f
o
r 3
r
d h
a
rm
o
n
ic
freque
ncy
co
mpone
nts. B
o
th freq
uen
cy control loo
p
s tog
e
the
r
give refe
ren
c
e sig
n
al to
shunt
conve
r
ters to
maintain co
nstant DC voltage of
the shunt conve
r
t
e
r and
con
s
t
ant 3rd ha
rm
onic
c
u
rrent injec
t
ed in to the grid.
3. Results a
nd Analy
s
is
In this se
ction
modeling of
DPFC a
nd si
mulation resu
lts are p
r
e
s
en
ted.
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IJEECS
ISSN:
2502-4
752
Analysis of DPFC in Powe
r System
Ne
t
w
ork for Im
provin
g Powe
r
Flow Control
(Kuldeep Sai
n
i)
516
3.1. A. Modeling of DPF
C
The
circuit
m
odel
of the
DPFC a
s
sho
w
n in
Figu
re
9
is a
simple
two a
r
ea
sy
ste
m
which
con
s
i
s
ts of major compo
n
e
n
ts: two three
phase
sou
r
ces, 3-p
h
a
s
e tran
smi
ssi
on lines,
∆
-Y pow
e
r
transfo
rme
r
s, one sh
unt co
nverter a
nd set of six serie
s
co
nverte
rs.
Figure 9. Simulation ci
rcuit of t
he DPFC with two
-
a
r
ea syste
m
[22]
The sy
stem
contai
ns two
buse
s
with
fix
ed voltage, whe
r
e the b
u
se
s a
r
e co
nne
c
ted
throug
h ind
u
c
tors. The
DPFC is pl
ace
d
betwe
en th
e two-bu
se
s with the send
ing end
and t
h
e
receiving e
n
d
bus voltag
es Vs and Vr, resp
ective
ly. The po
we
r flow bet
wee
n
the two b
u
ses is
obtaine
d by
providin
g a
p
hase a
ngle
d
i
fferenc
e b
e
t
w
ee
n the
bu
s voltag
e a
n
g
les.
The
sh
unt
conve
r
ter
of the DPF
C
is a singl
e ph
ase
univers
al
bridg
e
volta
g
e source
converte
r that
is
con
n
e
c
ted b
e
twee
n the neutral poi
nt of
∆
-Y transfo
rmer a
nd the
groun
d
, and
is powe
r
e
d
by
con
s
tant
DC
voltage source. The seri
es conve
r
te
rs o
f
the DPFC
use
a same
type of singl
e
pha
se
conve
r
ter that is
co
n
necte
d to the
tran
sm
issio
n
line by a
sin
g
le ph
ase lin
ear tran
sform
e
r.
There is
no p
o
we
r supply
at dc
side to
sup
port th
e
serie
s
conve
r
ter
DC voltag
e. Both the shun
t
and
seri
es
co
nverters u
s
e
GTO-diod
e a
s
the
swit
chi
ng device wit
h
PWM
control schem
e [2
3].
The si
mulatio
n
paramete
r
s of the DPFC device
a
r
e li
sted in the A
ppen
dix (see
Table 1
)
. Th
e
DPFC model
is sim
u
lated in M
a
tlab Simulin
k,
u
s
in
g SimPo
w
erSystems tool
box. The
DP
FC
simulatio
n
re
sults a
r
e di
scussed in two parts: i)
the a
c
tive and re
a
c
tive power flow thro
ugh t
h
e
transmissio
n
line at 1
o
tra
n
smi
ssi
on
an
gle
with
DP
F
C
system an
d
with
out DPFC system,
ii
)
the
DPFC b
ehavi
o
r in stea
dy
state and step
respon
se.
Ca
se- I: Simu
lation Model
without DPF
C
and
with DPFC
In this
case, the s
i
mulation model
with
out DPF
C
a
n
d
with
DPF
C
is
simul
a
ted
for 0.1
se
c to ob
se
rve the value
s
of active and
rea
c
tive po
wer flow th
rou
gh the tra
n
smissi
on lin
e. The
theoreti
c
al va
lues of po
we
r flow for with
out DPFC
an
d with DPFC
system a
r
e o
b
tained by Eqn.
(3) an
d Eqn.
(2) an
d
a
r
e
given a
s
: P
+
jQ=1
344.3
7
-j1
1
.73 VA a
nd
P+jQ
=67.76
-j
11.73 VA .T
h
e
simulate
d val
ues of a
c
tive and rea
c
tive power flo
w
s i
n
the line for
1o of tran
smi
ssi
on an
gle a
r
e
sho
w
n in Fig
u
re 10 a
nd Fi
gure 1
1
. The
output wave
forms can b
e
see
n
in the
MATLAB scope
block.
(a)
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IJEECS
Vol.
2, No. 3, Jun
e
2016 : 510
– 521
517
(b)
Figure 10. (a
) Active Power through the li
ne (b
) Re
acti
ve Power through the lin
e with 1o
transmissio
n angle
without
DPFC
(a)
(b)
Figure 11. (a
) Active powe
r
through the li
ne (b
) Re
acti
ve powe
r
thro
ugh the line
with 1o
transmissio
n angle
with DPFC
CaseII: DPFC behavio
r in steady state
and step response.
The
Simul
a
tion
mo
del with
DPF
C
i
s
simulated und
er steady
-sta
te
and step
cha
nge
con
d
ition
s
an
d their re
sult
s are sh
own in
Figure
s
(1
2)
to (19).
Ca
seII (A) Steady-state re
sults
Und
e
r stea
dy-state
conditi
ons
the se
rie
s
conv
e
r
ter is co
ntrolle
d to
inje
ct a fu
nd
amental
voltage of 2V
. The line
cu
rre
nt, voltage
injecte
d
by the serie
s
co
nverter
and t
he voltage
a
n
d
c
u
rr
en
t a
t
the
∆
-si
de
of the
tran
sformer
are
shown i
n
Figu
res (12) to (14).
Fo
r
co
nvenien
ce
on
ly
the waveforms in
on
e p
hase a
r
e
sh
own. T
he
co
nstant 3rd
h
a
rmo
n
ic cu
rrent
inje
cted by
the
shu
n
t conve
r
ter
evenly di
sperse
s to
the
thre
e p
h
a
s
e
s
a
nd i
s
supe
rimpo
s
e
d
o
n
the fund
ame
n
tal
curre
n
t as
sh
own i
n
Figu
re (12
)
. It is
observed f
r
o
m
Figure (13
)
that the vol
t
age inje
cted
by
seri
es
co
nve
r
ter i
s
a pul
se
width mo
dulated
(PWM) waveform contai
ning
two freq
ue
ncy
comp
one
nts. The amplitud
e of the waveform rep
r
e
s
e
n
ts the dc-ca
pacito
r
voltag
e at the line side
of the transf
o
rme
r
whi
c
h
is well mai
n
tained by exchangi
ng activ
e
power with
the line at
3rd
harm
oni
c freq
uen
cy.
Figure 12. DPFC ope
ratio
n
in steady-st
a
te: line curre
n
t
Evaluation Warning : The document was created with Spire.PDF for Python.
IJEECS
ISSN:
2502-4
752
Analysis of DPFC in Powe
r System
Ne
t
w
ork for Im
provin
g Powe
r
Flow Control
(Kuldeep Sai
n
i)
518
Figure 13. DPFC ope
ratio
n
in steady
-st
a
te: serie
s
co
nverter voltag
e
Figure 14. DPFC ope
ratio
n
in steady-st
a
te: bus volta
g
e and
curre
n
t at the
∆
sid
e
of the
trans
former
The voltag
e
and
cu
rre
nt
waveforms which
are sho
w
n in
Figu
re
(14
)
Contain
s
no thi
r
d-
harm
oni
c co
mpone
nt. This sh
ows the
third-
harmoni
c filtering p
r
o
perty of the Y-
∆
tr
an
s
f
orme
r
.
The step re
spon
se re
sults
are sh
ow
n in
Figures (1
5)
to (19
)
. A ste
p
ch
ang
e of t
h
e fund
ame
n
t
al
referen
c
e vol
t
age of the serie
s
co
nvert
e
r is ma
de a
s
sh
own in F
i
gure 1
5
(1
5). As sho
w
n in
Figure 16, the dc voltage of the
serie
s
conve
r
ter is
stabilize
d
befo
re and after t
h
e step chan
ge
and a
p
h
a
s
e shift
of
th
e se
ries conve
r
ter
voltage
i
s
ob
serve
d
at 0.2
8
5
simulatio
n
time. Th
e lin
e
curre
n
t thro
u
gh the lin
e is sho
w
n i
n
Fi
gure
17.
It is observed
th
at the ch
ang
e in the volta
g
e
injecte
d
by t
he seri
es
co
nverter
ch
an
ges th
e
curre
n
t flowing
through th
e lin
e
.
The a
c
tive
and
rea
c
tive powers inj
e
cte
d
o
r
absorbed by
the
serie
s
co
nverter a
r
e shown in Figu
re 18.
Figure 15. Re
feren
c
e volta
ge for the seri
es converte
rs
Figure 16. Step re
spo
n
se of DPFC: se
ri
es converte
r
voltage
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ISSN: 25
02-4
752
IJEECS
Vol.
2, No. 3, Jun
e
2016 : 510
– 521
519
Figure 17. Step re
spo
n
se of
the DPFC: line cu
rrent
Figure 18. Step re
spo
n
se of the DPFC: active
and re
active po
wer i
n
jecte
d
by the seri
es
conve
r
ter at the fundam
ent
al freque
ncy
Figure 19. Step re
spo
n
se of the DPFC
: bus voltag
e a
nd cu
rrent at the
∆
sid
e
of the tran
sform
e
r
It is o
b
serve
d
from
Fig
u
re (19) that t
he
∆
-sid
e of
the
network co
ntain
s
no
3rd h
a
rm
on
ic
comp
one
nt and a pha
se
shift of the current is ob
serv
ed in wavefo
rms
4. Conclusio
n
This p
ape
r prese
n
ts a n
e
w powe
r
flow
cont
roller within the FACTS
family, c
a
lled
DPFC.
The main o
b
j
e
ctive of this pape
r is to mi
nimize
the li
mitations of the co
nventio
nal UPF
C
thu
s
to
reduce the
cost and
increase the reliability of
the system, and to v
e
rify the principle and control
of the DPFC in the real tra
n
sm
i
ssi
on ne
twork. The DPFC whi
c
h
is emerg
e
d fro
m
the UPFC
by
eliminating th
e com
m
on d
c
link
betwee
n
the sh
unt
and seri
es
converte
r, can
simultan
eou
sly
control all the
para
m
eters
of the
system
as the
UPFC. As far as
co
st and
relia
bility concern
s
t
h
e
DPFC h
a
ve two maj
o
r ad
vantage
s ove
r
UPF
C
ve
ri
fy, that
the DPFC sol
u
tion
is economi
c
al
than UPF
C
:
1) the
se
rie
s
conve
r
ter of
the
DPF
C
u
s
e the
D-FA
CTS con
c
ept
, which em
pl
oys
multiple low
rated sin
g
le-p
hase se
rie
s
converte
rs
in
st
ead of the si
ngle large po
wer
rated three-
phase seri
es
converter that incr
eases the reliabilit
y of the DPF
C
during seri
es converter
failures;
2) the hig
h
voltage and
curre
n
t ratin
g
of t
he co
mpone
n
ts a
n
d
the high v
o
ltage isolati
o
n
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