TELKOM
NIKA Indonesia
n
Journal of
Electrical En
gineering
Vol. 13, No. 1, Janua
ry 201
5, pp. 10 ~ 1
9
DOI: 10.115
9
1
/telkomni
ka.
v
13i1.680
9
10
Re
cei
v
ed O
c
t
ober 6, 20
14;
Revi
se
d No
vem
ber 18, 20
14; Accepted
De
cem
ber 1
0
,
2014
Inter-Harmonics in Voltage-Sourced Converters based
High Voltage Direct Current Systems
Phuchu
y
Ngu
y
en*
1
, Minxiao Han
1
, Wenli Yan
2
1
School of Elec
trical an
d Elect
r
onic En
gin
eer
i
n
g
2
School of Mat
hematic
al & Ph
ysic
al Sci
ence,
North Chi
na El
ectric Po
w
e
r U
n
iversit
y
,
Beiji
ng, Ch
in
a, 010-
519
71
64
5
*Corres
p
o
ndi
n
g
author, e-ma
i
l
: hu
ynp
@
ep
u.
edu.vn
A
b
st
r
a
ct
Voltag
e-So
urced Co
nverter (
VSC) is the
main
co
mpo
n
e
n
t in a VSC-
bas
ed Hi
gh V
o
lta
ge Dir
ec
t
Current (HVDC) system
. In
addition to the characteris
t
ic har
m
o
nics,
the inter-
har
m
o
nics c
ould be
origi
nate
d
from the characteri
stic
of each co
nverter w
o
rkin
g at different
mo
du
latio
n
freque
ncies, or fro
m
a
distorting frequency on one or both ac (or dc) syst
ems. The space vector
repres
entatio
n of VSC’
s
sw
itching funct
i
ons
is use
d
a
s
a tool for
an
aly
z
i
n
g a
nd
giv
i
ng th
e u
nderst
and
ing
how
th
e inter-
har
mo
ni
cs
app
ear. Base
d
on the
meth
odo
log
i
cal
an
a
l
ysis, simul
a
tio
n
mod
e
ls w
e
re bui
lt an
d i
m
ple
m
ented
usi
n
g
Sim
P
owerSystem
s in MATLAB for cases.
The si
mul
a
tio
n
results show
that, a series of inter-har
monics
is
prod
uced
tend
to be
do
mi
na
nt in l
o
w
-
frequ
ency ra
ng
e, es
peci
a
lly th
e n
e
gative-s
equ
enc
e inter-
har
mo
ni
cs
w
h
ich h
a
ve
lo
w
e
r freque
nci
e
s than
the
fun
d
a
m
e
n
ta
l. T
h
is
el
abor
ate
und
erst
and
ing
of VSC-bas
ed H
V
D
C
system’
s
inter-
har
m
o
nic
char
acteri
stic could be
benefic
ial to
har
m
o
nic m
e
asur
em
ent and
m
i
tigation
control.
Ke
y
w
ords
: vol
t
age sourc
ed c
onverter, VSC-
base
d
HVDC,
i
n
ter-har
monic,
sw
itching functi
on
Copy
right
©
2015 In
stitu
t
e o
f
Ad
van
ced
En
g
i
n
eerin
g and
Scien
ce. All
rig
h
t
s reser
ve
d
.
1. Introduc
tion
The Volta
ge-Sourced
Con
v
erter
ba
sed
High
Voltage
Dire
ct Cu
rre
n
t
(VSC-
b
a
s
ed
HVD
C
)
system
s h
a
ve bee
n utili
ze
d in p
o
wer
system for ma
ny years fro
m
the first te
st in 1
997. S
o
me
advantag
es o
f
VSC-ba
s
ed
HVDC incl
ud
e [1]: Independent
control
of active and
rea
c
tive power;
Possi
bility to sup
p
ly pa
ssive
we
ak netwo
rks
and b
a
ck-st
a
rt ca
pabilit
y; High dyn
a
mic
performance;
Multi-terminal possibility.
Ho
wever,
VSC-b
ased
HVDC produ
ci
ng h
a
rm
oni
cs o
n
both
a
c
-side
a
nd
d
c
-side
i
s
inherent by t
he VSC itsel
f, called
cha
r
acte
ri
st
ic
ha
rmoni
cs, an
d
will i
n
tera
ct
with
harmo
nic
distortio
n
s al
ready
existe
d in the
sy
stem. The
ch
a
r
acte
ri
stic
ha
rmoni
cs of V
S
C a
r
e di
re
ctly
asso
ciated
with the type of VSC technolo
g
ies,
m
odulatio
n techniqu
es a
n
d
the swit
chi
ng
freque
ncy [2]. When the
ac supply is
unbal
an
ced
or one
side
of VSC cont
ains b
a
ckg
r
o
und
harm
oni
cs, th
ere a
r
e no
n-cha
r
a
c
teri
stic harmo
nics
o
n
both a
c
- a
nd dc-side of
the VSC [3, 4].
Inter-h
arm
oni
cs
are th
e n
on-inte
gral n
on-cha
r
a
c
teri
stic h
a
rm
oni
cs, whi
c
h a
r
e
cau
s
e
d
by an
AC/DC/A
C
sys
tem operating with different fr
eq
u
enci
e
s on t
he both ac-side
s
[5]. Well
unde
rsta
ndin
g
these ha
rm
onics will co
ntribute to
establish ad
equ
ate approa
ch
es to harmon
i
c
eliminating, i
m
provin
g t
he system p
e
rfo
r
mance.
Several works have stu
d
i
ed harmoni
c intera
ctio
ns betwee
n
the two sid
e
s of the
conve
r
ter
an
d thro
ugh th
e
dc-link of HV
DC [3
-8]. In
[3], the harm
o
nic tran
sfer
chara
c
te
risti
c
of a
curre
n
t
source
converte
r b
a
se
d HVDC has
be
en an
alyzed. In
th
e case of th
e
two
ac sy
ste
m
s
are a
s
yn
chro
nou
s, a ba
ckgrou
nd ha
rm
onic from
on
e end a
c
sy
stem will be transfe
rred to the
other e
nd an
d pro
d
u
c
es t
w
o inte
r-h
arm
onics. Fo
r th
e
VSC-ba
s
e
d
HVDC sch
e
m
e
, a non-i
n
te
gral
harm
oni
cs on the dc-si
de
will
ca
use two inter-harm
o
nics
on the ac-side [4]. The am
plitudes
of
inter-harmoni
cs dep
end on
the
imped
an
ce
s
on both ac
- and
dc-si
de of the
con
v
erter [6, 7].
For
a practi
cal
project i
n
[8], h
a
rmo
n
ic emi
s
sion
fr
om
wi
n
d
turbi
n
e
s
, which
contain
s
VSCs,
ha
s b
een
measured an
d sho
w
e
d
tha
t
group
s of int
e
r-harm
oni
cs appe
arin
g in the output
current spe
c
trum
.
These inter-h
a
rmo
n
ics are mainly gathe
red and
signifi
cant in the lo
w-frequ
en
cy range.
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
Inter-Harm
oni
cs in Voltag
e-Sourced
Con
v
erte
rs
ba
sed
High Voltage
Dire
ct… (Ph
u
ch
uy
Ngu
y
e
n
)
11
The ha
rmo
n
i
c
tran
sfe
r
chara
c
te
risti
c
of VSC
is i
n
vestigated in this paper, which
con
s
id
ers bot
h the fundam
ental and hi
g
h
-o
rde
r
sw
itching compo
n
ents of the V
S
C’s
swit
chin
g
function
s. Thi
s
is a contra
st to all previous
an
alyse
s
whi
c
h have ju
st con
s
id
ere
d
the fundame
n
tal
swit
chin
g co
mpone
nt. In fact, the hi
gh-orde
r
swit
chi
ng comp
one
nts have
si
gn
ificant effect
s on
the amplitud
e and the
seque
nce
of harm
oni
cs.
By using the
swit
chin
g function
s of V
S
C
rep
r
e
s
ente
d
in sp
ace vect
or form, the
o
r
igin
a
nd
cha
r
acte
ri
stic of i
n
ter-harmoni
c on VSC-b
a
s
ed
HVDC
syste
m
s a
r
e
also i
n
vestigate
d
. In an
asyn
ch
ronou
s HVDC
con
n
e
c
tion who
s
e ac
gri
d
s
differ in frequency, one
end converter’s dc-side c
haracteri
stic
harmonics
will be the ripples
to
the othe
r e
n
d
converte
r.
Con
s
e
quently
, these
ri
p
p
le
s
could
ind
u
c
e inte
r-ha
rm
onics o
n
the
a
c
system
s. Th
e
disto
r
ting
in
freque
ncy
of
one
ac
sy
ste
m
could
al
so
ca
use inte
r-harm
oni
cs to
be
prod
uced i
n
the sy
stem al
so. Fu
rthe
rm
ore, a
ba
ckground ha
rmoni
c
in one end
ac system
wil
l
be
transfe
rred to
the other en
d ac sy
stem
and produ
ce
s a serie
s
of in
ter-h
arm
oni
cs.
Und
e
r th
e m
a
thematical a
nalysi
s
, the i
n
ter-
harmoni
c cha
r
a
c
teri
st
ic can
be
stu
d
ied by
usin
g the
si
mulation
mo
del in
Figu
re 1. T
he
sy
stem’s pa
ra
meters m
a
y be
ch
ang
e
d
in
corre
s
p
ondin
g
to each ca
se of study. In conve
r
ter stations, rea
c
t
o
rs a
r
e in
stal
led on the both
side
s
of the
converte
rs.
Th
e tra
n
sfo
r
me
r win
d
ing
is Y
n
/Y co
nne
ctio
n type
whe
r
e
the Y
windi
ng
is
on the
conve
r
ter-side, resul
t
ing in de
cou
p
ling the a
c
system from th
e triple h
a
rm
onics p
r
od
uced
by
the co
nve
r
ter.
T
he ac high-
pa
ss filter
gro
up i
s
an e
s
sential
part
of the
schem
e, lo
cat
e
d
betwe
en the
conve
r
ter
transfo
rme
r
and the
co
nverter
rea
c
tor for imp
r
oving filterin
g
cha
r
a
c
teri
stic. The dc-si
d
e of the VSC uses
re
se
rvoir dc
cap
a
c
itors to equ
alize d
c
volta
ge,
enha
nce the
system dyn
a
mics, and
redu
ce th
e
dc-sid
e volta
ge rip
p
le
s, whe
r
e the
most
domina
n
t 3
rd
harm
oni
c will
be filtered out
by the 3
rd
order tuned filters.
2. Rese
arch
Metho
d
2.1. VSC’s Operatio
n Principle
In Figure
2, a three
-
leve
l NPC VSC
force
s
the a
c
-side volta
g
e
to a ce
rtai
n value
determi
ned
b
y
the given switchi
ng fun
c
tions. Corr
e
s
pondi
ng to th
ree voltag
e l
e
vels, the
switch
of
pha
se
x
t
a
ke
s t
h
e
v
a
lue
k
x
=1,
k
x
=0, a
nd
k
x
=-1, re
spectively swit
chin
g
to
th
e positive dc
p
o
le,
the “midp
o
int
,
” and the n
egative dc p
o
le. For
the
VSC usin
g p
u
lse
-
wi
dth m
odulatio
n (P
WM)
techni
que, th
e k
x
=1
an
d
k
x
=-1 corre
s
po
nd to th
e
po
sitive an
d n
e
gative half
cycle m
odulati
on
wave, res
p
ectively.
In orde
r to redu
ce ha
rmo
n
ic level, the
naturally
sa
mpled p
h
a
s
e
disp
osition
PWM i
s
adopte
d
. The
switching
states of valves are d
e
fined
by compa
r
in
g the sinu
soi
dal modul
atio
n
wave
with t
w
o
high f
r
eq
uen
cy trian
g
u
lar
ca
rri
ers.
Using th
e
doubl
e Fo
uri
e
r a
nalysi
s
,
the
expre
ssi
on o
f
switching f
unctio
n
of p
hase
x
(with
“
x
= a, b, c
”
also use
d
for all follo
wing
equatio
ns
) of a three
-
level
conve
r
ter in ti
me domai
n is given by the followin
g
Equ
a
tion [2]:
2n
1
x1
x
m
2
,
4
,
6
...
n
c1
x
km
2
m
1
,3
,5
.
.
.
n
c1
x
Jm
M
c
o
s
n
21
kt
M
c
o
s
t
m
co
s
m
t
2
n
1
t
Jc
o
s
n
81
co
s
m
t
2
n
t
m
(1)
Whe
r
e: M is the modul
atio
n index;
1
is the
frequen
cy of the modulation wave;
c
is the
freque
ncy of the carrie
r wave; m is the group in
dex
(multiple of switchi
ng freq
uen
cy); n is th
e
Transfo
rmer
Reacto
r
AC f
ilter
Re
actor
Reacto
r
(a)
(b)
Figure 1. Model system fo
r analyzi
ng in
ter-h
arm
oni
c cha
r
a
c
teri
stic. (a) Sy
stem block dia
g
ra
m;
(b) Re
ctifier/Inv
e
rter statio
n
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 13, No. 1, Janua
ry 2015 : 10 – 1
9
12
side
ban
d ha
rmonic ind
e
x
from e
a
ch g
r
oup;
x
is the
modulatio
n
wave ph
ase
shift for ea
ch
pha
se x;
is
the carrier
wave phase
shift;
2n
1
2
k
1
J,
J
is
the firs
t k
i
nd B
e
ssel func
tions
(s
ee
Appendix A); and
km
J
is defined in (2).
km
2
k
1
k1
2k
1
JJ
2
m
1
M
2k
2
n
1
2
k
2
n
1
(2)
Figure 2. Three-level volta
ge so
urced
conve
r
ter p
h
a
s
e qu
antities.
Figure 3. Step function
s of
phase a
The
swit
chin
g functio
n
s a
r
e u
s
e
d
to d
e
t
ermine th
e relation
ship
s
betwe
en the
both si
de
quantitie
s of the co
nverte
r. Gene
rally, these rela
tion
ships
can b
e
e
x
presse
d in (3) for ph
ase
x
.
xx
x
d
ut
k
t
u
t
(3)
Whe
r
e:
xd
p
x
p
n
xn
ut
u
t
k
t
u
t
k
t
(4)
In (4
), u
p
(t) a
nd u
n
(t) a
r
e
d
c
-side
po
sitive an
d ne
gative pol
e voltag
es, respe
c
tively; k
xp
(t)
and k
xn
(t) a
r
e
step
fun
c
tion
s
co
rre
sp
ondi
ng to
ea
ch
h
a
lf cycl
e
of p
hase x m
odul
ation
wave, a
s
sho
w
n in Fig
u
re3.
It can be see
n
that, for ph
ase
a
, k
ap
(t)-
k
an
(t) = 1 an
d [k
ap
(t)
+
k
an
(t)] i
s
a pe
riodi
c f
unctio
n
,
and thu
s
ca
n be expan
ded
by a Fourie
r serie
s
as [6]:
ap
an
1
h
1
,
3
,
5
...
41
h
kt
k
t
s
i
n
c
o
s
h
t
h2
(5)
Adding -2
π
/3
and 2
π
/3 to
the pha
se
a
ngle of e
a
ch
harm
oni
c co
mpone
nt in (5) will
derive the correspon
den
ce
forms of
ph
ase b and c, respectively.
The dc-side
current on the
positive d
c
pole is
es
tab
lished in (6).
da
a
b
b
c
c
it
k
t
i
t
k
t
i
t
k
t
i
t
/
2
(6)
In the ca
se of
u
p
(t)=
- u
n
(t) =
u
d
(t)/2, the relation
ship
s b
e
tw
ee
n ac- a
nd dc-side q
u
antities
of VSC , with
out the
ze
ro
seque
nce com
pone
nts,
no
w ca
n be
dete
r
mined i
n
the
gene
ral fo
rm
ula
of the spa
c
e
vector [4]:
Vd
*
dV
ut
K
t
u
t
/
2
3
it
R
e
K
t
i
t
4
(7)
t
u
a
t
u
b
t
u
c
t
k
a
t
k
b
t
k
c
t
i
a
t
i
b
t
i
c
p
ut
d
C
2
d
C
2
1
-1
-1
-1
1
1
n
ut
0
0
0
d
it
ap
kt
an
kt
0
1
1
2
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
Inter-Harm
oni
cs in Voltag
e-Sourced
Con
v
erte
rs
ba
sed
High Voltage
Dire
ct… (Ph
u
ch
uy
Ngu
y
e
n
)
13
Whe
r
e:
VV
ut
,
i
t
are
spa
c
e
vect
or of a
c
-sid
e
voltage an
d
cu
rre
nt re
spectively;
dd
ut
,
i
t
are the
dc-si
de voltage
an
d cu
rrent, re
spectively;
Kt
is t
he spa
c
e ve
ctor of thre
e
-
sinu
soi
dal switching fun
c
tio
n
s.
2.2. Space Vector
Repr
es
enta
tion of S
w
i
t
ching Fu
nctions
As can b
e
se
en from (1
), the first term
gi
ves the fun
damental
co
mpone
nt of switchi
ng
function. Its
amplitude
ju
st is d
epen
de
nt on th
e mo
dulation
inde
x, but is i
n
d
epen
dent of
the
freque
ncy i
n
d
e
x, m
f
=
ω
c
/
ω
1
,
and carri
er phase shift.
T
he
amp
litudes of
other
harmonics depend
on the cha
r
a
c
teri
stic of the Bessel fun
c
tion,
whi
c
h
are eq
ual for two sideb
an
d harmo
nics
on
oppo
site si
de
s of the cente
r-pl
a
ced ha
rmonic in e
a
ch grou
p.
In ea
ch
gro
up of
ca
rri
er sid
eba
nd
s,
t
he hig
h
-o
rd
er
swit
chin
g
co
mpon
ents sati
sfy
0
fm
n
mm
n
3
i
N
, where i is a
n
integer, a
r
e
called
zero-seque
nce switchin
g com
p
o
nents. It is
clea
r from
(6
) that the d
c
curre
n
t is n
o
t affe
cted by t
he zero
se
qu
ence switchin
g com
pon
ent
s.
The hig
h
-o
rder
swit
chin
g com
pon
en
ts sati
sfy
fm
n
mm
n
3
i
1
N
are
calle
d positive-
seq
uen
ce
switchi
ng co
mpone
nts. And the ot
he
r
high-ord
e
r swit
chin
g
co
mpone
nts sa
tisfy
fm
n
mm
n
3
i
1
N
are
called
n
egative-seq
u
ence swit
ch
i
ng comp
one
nts.
As
a re
sult,
the
spa
c
e ve
ctor of switchi
n
g function
s is com
p
o
s
ed
of three co
mpone
nts ex
pre
s
sed a
s
the
followin
g
equ
ation:
1m
n
m
n
m1
n
m
1
n
Kt
K
t
K
t
K
t
(8)
Whe
r
e:
1
mn
1
mn
1
jt
1
jN
t
mn
mn
jN
t
mn
mn
Kt
M
e
ˆ
Kt
K
e
ˆ
Kt
K
e
(9)
In (9
),
mn
ˆ
K
and
mn
ˆ
K
are the
a
m
plitude
s of
the
po
sitive- a
nd
neg
ative-se
que
nce
swit
chin
g co
mpone
nts, re
spe
c
tively. It is cl
ea
r
that, the ze
ro
-seq
uen
ce
swit
chi
ng comp
one
nts,
whi
c
h ha
s trip
le orde
rs, doe
s not app
ear.
2.3. Ripples on DC-side c
a
used by
Harmonics Tra
n
sfer
red fr
o
m
AC-side
Practi
cally, many VSC-b
ase
d
HV
DC syst
em
s a
r
e asyn
ch
ron
ous i
n
tercon
nectio
n
s
who
s
e
ac g
r
ids have
di
fferent fund
a
m
ental fr
e
q
u
enci
e
s. M
o
reover, fo
r the syn
c
h
r
o
n
ous
interconn
ecti
on b
e
twe
e
n
two
ide
n
tical fre
que
ncy
ac
system
s, there
may
be
di
stortin
g
in
freque
ncy in
operation. Fo
r the
s
e
sche
mes, the
dc-side
ch
ara
c
te
ristic ha
rmoni
cs
of one
en
d
conve
r
ter co
uld be acte
d as the dc-sid
e rippl
es to the converter at the opposite e
nd.
Con
s
e
quently
, the both en
d conve
r
ters
will ope
rate
t
o
cau
s
e th
e d
i
fferent harm
onic
spe
c
tru
m
o
n
their both a
c
-
and d
c
-side.
Assu
ming a
c
-sid
e current
s of the co
nverter 1
su
perim
po
se h
a
rmo
n
ic
com
pone
nts
expre
s
sed in
the spa
c
e ve
ctor form as:
hh
jt
j
t
Vh
h
h
ˆ
ˆ
it
i
e
i
e
(10
)
The first pa
rt in (10) i
s
the positive-se
qu
ence harm
oni
c, and the se
con
d
is the n
egative-
seq
uen
ce ha
rmoni
c. Substituting (10) to the se
con
d
equation i
n
(7) with th
e expre
ssi
on
of
swit
chin
g fun
c
tion a
s
(8
), we get:
dh
d1
h
d
m
n
h
d
m
n
h
m1
n
m
1
n
i
t
i
t
it
it
(11
)
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02-4
046
TELKOM
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KA
Vol. 13, No. 1, Janua
ry 2015 : 10 – 1
9
14
Whe
r
e:
h1
h
1
mn
1
h
mn
1
h
mn
1
h
m
n
1
h
jt
j
t
d1h
h
h
jN
t
j
N
t
mn
dm
h
h
h
jN
t
j
N
t
mn
dm
h
h
h
3M
ˆˆ
it
R
e
i
e
i
e
4
ˆ
3K
ˆˆ
it
R
e
i
e
i
e
4
ˆ
3K
ˆ
ˆ
it
R
e
i
e
i
e
4
(12
)
In the case o
f
a balance
d
harm
oni
c, the ac
-side h
a
s j
u
st only the positive or n
e
gative-
seq
uen
ce h
a
rmonic. Equ
a
tion (12
)
sho
w
s that, only one sid
eba
nd
harm
oni
c to be pro
d
u
c
ed
on
the dc-si
de for ea
ch
seq
uen
ce of the
harmo
ni
c.
The interacti
on of the p
o
sitive-seq
ue
nce
swit
chin
g co
mpone
nts
(in
c
ludi
ng the f
undam
ental
comp
one
nt) contrast with
the
neg
ative
-
seq
uen
ce
swi
t
ching
compo
nents; th
e p
o
s
itive-s
equ
en
ce harmoni
c offers
l
o
wer orde
r sid
eba
nd,
while the n
e
g
a
tive-se
que
n
c
e ha
rmo
n
ic
offers hig
h
e
r
orde
r on
e.
Whe
n
the a
c
-side h
a
s
an
unbal
an
ced h
a
rmo
n
ic
, it ha
s both the p
o
sitive- an
d ne
gative-
seq
uen
ce
co
mpone
nts a
s
in
(10
)
. T
herefore,
th
ere
will
b
e
two si
deba
nd harm
onics on
the dc-
side,
but thei
r am
plitude
d
epen
ds
on th
e amplitu
de of
the
o
r
igin comp
one
nts on
the ac-sid
e,
r
e
spec
tively.
2.4. Inter-h
a
r
m
onics on the AC-sid
e c
a
used by
the DC-link ripp
les
Assu
me th
at
the d
c
-sid
e v
o
ltage
co
mpri
se
s a
ri
pple
with a
ngle
freque
ncy
r
, w
h
ic
h
is
not an intege
r of the fundamental, writte
n in the form as:
rr
jt
jt
dr
d
r
r
d
r
ˆ
ˆ
ut
u
c
o
s
t
u
e
e
/
2
(13
)
Und
e
r the i
n
tera
ction
of th
e zero-seq
ue
nce
switching
co
mpo
nent
s, the
dc-si
de
h
a
rmo
n
ic
voltage tran
sfer thro
ugh V
S
C can b
e
explaine
d in
(14
)
for example
of phase a ou
tput voltage:
dr
r
00
0
a.
m
n
r
m
n
m
n
1
0
00
mn
d
r
mn
1
r
mn
1
r
ˆ
uc
o
s
t
ˆ
ut
K
c
o
s
N
t
2
ˆ
ˆ
Ku
c
o
s
N
t
c
o
s
N
t
4
(14
)
These a
dditio
nal ha
rmo
n
ics a
r
e all
ze
ro
-se
que
nce h
a
rmo
n
ics, an
d t
herefore, t
hey will
not appe
ar in
line voltage.
For th
e othe
r switchi
ng
co
mpone
nts,
su
bstitute (13
)
t
o
the first e
q
uation in
(7)
with the
expre
ssi
on of
switching fun
c
tion a
s
(8
), we get:
Vr
1
r
mnr
m
nr
m1
n
m
1
n
u
t
u
t
ut
ut
(15
)
Whe
r
e,
r1
r
1
mn
1
r
mn
1
r
mn
1
r
mn
1
r
jt
j
t
1r
dr
jN
t
j
N
t
mn
mn
r
d
r
jN
t
j
N
t
mn
mn
r
d
r
M
ˆ
ut
u
e
e
4
ˆ
K
ˆ
ut
u
e
e
4
ˆ
K
ˆ
ut
u
e
e
4
(16
)
As ca
n be
se
en from
(16
)
, there a
r
e two side
ban
d in
ter-h
arm
oni
cs in the ac-si
d
e of the
VSC, co
rre
spondi
ng to a
ripple
on th
e dc-side.
Under the int
e
ra
ction
of the fund
ame
n
tal
swit
chin
g
co
mpone
nt, the
high
er
order inter-ha
rmo
n
i
c i
s
a
po
sitive-sequ
en
ce
compon
ent, a
nd
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TELKOM
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ISSN:
2302-4
046
Inter-Harm
oni
cs in Voltag
e-Sourced
Con
v
erte
rs
ba
sed
High Voltage
Dire
ct… (Ph
u
ch
uy
Ngu
y
e
n
)
15
the lower o
r
der i
s
a n
e
g
a
tive-se
que
n
c
e o
ne if
r1
, and vice ve
rsa. Whe
r
ea
s,
unde
r the
intera
ction of the
hig
h
-freq
uen
cy
switchi
ng comp
on
e
n
t
s, if the freq
uen
cy of the
dc-sid
e
rippl
e
is
smalle
r th
an
the fre
quen
cy of switchi
n
g compo
nent
s, the
se
que
nce
of the
two-si
deb
and
in
ter-
harm
oni
cs o
n
ac-side i
s
the same
seq
u
ence as the
switchi
ng com
pone
nts.
2.5. Inter-h
a
r
m
onics on the AC-sid
e c
a
used
the DC-c
apa
c
itor
Ripples
In the three
-
level NP
C
VSC, the midpoint curre
n
t contai
ns
large thi
r
d
-
h
a
rmo
n
ic
comp
one
nt, cau
s
in
g the third
-
ha
rmo
n
ic voltage (the
ripple
)
on th
e dc
cap
a
cit
o
r. Thi
s
voltage
harm
oni
c in turn re
sult
s in
low-o
r
de
r voltage ha
rmo
n
ics on the ac-sid
e of the conve
r
ter [9].
More
over, th
e midpoi
nt cu
rre
nt co
uld flo
w
through
the
earth
retu
rn
path bet
wee
n
two en
ds
of the
dc-li
n
k. In the
case of the two a
c
sy
ste
m
s have diffe
rent freq
uen
cies, low-o
r
de
r inter-h
arm
o
n
i
cs
may be prod
uce
d
on one
end ac
syste
m
beca
u
se of
the dc capa
citor rip
p
le
s o
f
the other end.
Assu
ming
tha
t
the ri
pple
o
n
the
dc
cap
a
citor at
th
e
end
2 of
the
dc-li
n
k
cau
s
e
d
by the
mid
point
curre
n
t from the end 1 i
s
e
x
presse
d as
(17):
3r
3r
1
ut
U
c
o
s
3
t
(17
)
The
dc po
sit
i
ve and
ne
g
a
tive pole
voltage
s n
o
w ca
n b
e
writ
ten a
s
the
followin
g
equatio
n:
pd
3
r
1
nd
3
r
1
ut
U
/
2
U
c
o
s
3
t
ut
U
/
2
U
c
o
s
3
t
(18
)
Ju
st con
s
ide
r
ing the
se
co
n
d
pa
rts i
n
(18
)
an
d
sub
s
titu
te them into
(4) fo
r the
co
n
v
erter
2, we get for the ca
se of ph
ase
a
:
3r
ad
1
2
h
1
,3
,5.
.
.
4U
1h
ut
s
i
n
c
o
s
3
h
t
h2
(19
)
Und
e
r the i
n
teractio
n of the fund
amen
tal swit
ching
comp
one
nt, the pha
se
a
output
voltage on th
e ac sy
stem
2 coul
d be a
c
hieved by su
bstituting (1
9) into (3), expressed in (20
)
.
dc
3
r
a2
2
1
2
2
h
1
,3
,5
.
.
.
MU
MU
1h
ut
c
o
s
t
s
i
n
c
o
s
3
h
t
2h
2
(20
)
From
(20
)
, the additio
nal
inter-harmo
nics may h
a
ve small
e
r freque
ncy t
han the
fundame
n
tal whi
c
h co
uld d
a
mage rotating machine c
onne
cted to the system, e
s
pe
cially in case
of negative-seque
nce harmonics.
2.6. Inter-h
a
r
m
onics und
er Unsy
mmetrical Con
d
itions
Whe
n
the p
o
i
n
t of comm
o
n
co
upling
(P
CC) on th
e a
c
sy
stem 1 i
s
subj
ecte
d to
single
pha
se-to
-
g
r
o
und fault, the
HVDC sy
ste
m
will op
erat
e und
er u
nba
lanced
condit
i
ons, a
nd VSC is
quite se
nsitiv
e to the negat
ive-se
que
nce
compo
nent i
n
the ac volta
ge [10].
Based
on
th
e theo
ry of
symmetrical
com
pon
ents,
an u
nbala
n
ced three
-
pha
se
cu
rrent
comp
ri
se three bal
an
ced
comp
one
nts
of positiv
e-, negative- an
d
ze
ro
-sequ
e
n
ce com
pon
e
n
ts.
The mathem
atical expression of pha
se
x
cu
rrent is th
e followin
g
eq
uation:
0
sx
s
1
x
s
1
x
s
ˆ
ˆ
it
I
c
o
s
t
I
c
o
s
t
i
t
(21)
Whe
r
e
ss
ˆ
ˆ
I,
I
are th
e cu
rre
nt am
plitude of po
siti
ve- an
d n
egative-seq
u
ence co
mpo
n
ent,
r
e
spec
tively;
is the
pha
se
a
ngle of th
e n
e
gative-sequ
e
n
ce
compo
n
e
n
t, relative to
the po
sitive-
seq
uen
ce co
mpone
nt.
The
spa
c
e v
e
ctor corre
s
p
ondin
g
to three-
p
h
a
s
e cu
rrent without the
ze
ro
-seq
uen
ce
comp
one
nt is:
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ISSN: 23
02-4
046
TELKOM
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KA
Vol. 13, No. 1, Janua
ry 2015 : 10 – 1
9
16
1
1
jt
jt
ss
s
ˆ
ˆ
it
I
e
I
e
.
(22
)
Equation
(22
)
has
a simil
a
r form a
s
(10)
for unb
alan
ce
d harmoni
cs. As a result, a se
rie
s
of ripple
s
will
be ind
u
ced
on the d
c
-si
d
e of t
he
conv
erter
wh
ere the comp
one
nt with fre
q
u
ency
1
2
is domin
ant. Again, this dominant com
pone
nt is
con
v
eyed to the
ac sy
stem 2 to prod
uce a
seri
es of int
e
r-harmoni
cs, wh
ere
the negative-se
q
uen
ce and p
o
sitive-seq
ue
nce
compo
n
ents
have frequ
en
cie
s
at
12
2
and
12
2
, res
p
ec
tively, are dominant.
3. Simulation and Result Anal
y
s
is
Simulation m
odel
s we
re
set up for the
VSC-ba
s
e
d
HVDC sy
ste
m
on Fig
u
re
1 usi
n
g
SimPowe
r
System
s in Matlab. In each
model, the se
nding e
nd VSC wa
s mo
del
e
d to ope
rate
as
power dispat
che
r
while
th
e receiving
e
nd VSC wa
s modele
d
to
o
perate
a
s
dc voltage regul
ator
and re
active power control
l
er. In each V
S
C stati
on, the VSC is a 6-IGBT bridge t
h
ree
-
level NP
C
conve
r
ter. T
h
e VSCs ad
o
p
t the SPWM mod
u
latio
n
techniqu
e.
The frequ
ency of the tria
n
g
le
carrie
r
wave i
s
27
times of
the funda
men
t
al frequ
en
cy. The
paramet
e
rs of ea
ch
m
o
del a
r
e
give
n
in the Appen
dix.
For
acce
pta
b
le
corre
c
tne
s
s of me
asu
r
eme
n
t both
harmoni
c
s
and inte
r-ha
rmonics,
Fouri
e
r
analy
s
is wa
s i
m
pl
emented
wit
h
a n
u
mb
e
r
cycle
win
d
o
w
s
wa
s cho
s
e
n
ho
w to
get
a
suitabl
e resol
u
tion
spe
c
tru
m
for
both t
w
o
system
s.
For
example,
acco
rdin
g to
IEC-6
100
0-4
-
7
stand
ard, a
10 (for 50
Hz system
s) o
r
12 (for
6
0
Hz
sy
st
em
s)
cy
cle win
d
o
w
s
wa
s cho
s
en,
therefore a spectrum with
5 Hz
resolution will be achi
eved [5].
3.1. Case 1
:
T
w
o
AC Sy
st
ems Opera
t
e
at 50 Hz
(a)
Dc-si
de volta
ge wavefo
rm
(b)
Dc-si
de volta
ge sp
ectrum
of case 1a
(c)
Dc-si
de volta
ge sp
ectrum
of case 1b
Figure 4. Ca
se 1: DC-sid
e voltage
(
a
) C
u
rr
ent
w
a
vefor
m
(b)
Cur
r
e
n
t
spe
c
t
r
um of
ca
se 1
a
(c
)
Cur
r
e
n
t
spe
c
t
r
um of
ca
se 1
b
Figure 5. Ca
se 1: ac
syste
m
2 phase cu
rre
nt
The first
ca
se
is the
ba
se-case
giving
a
comp
arative
view to
the
other cases. A
s
ca
n
be
see
n
fro
m
(1
), the o
u
tput
voltage of th
e VSC
will h
a
ve the fu
nd
amental
co
m
p
one
nt and
the
carrie
r multipl
e
side
ban
ds.
Becau
s
e of t
he ac hi
gh-
p
a
ss filters, th
e harm
oni
c o
r
de
rs e
qual t
o
o
r
highe
r tha
n
2
7
si
gnifica
ntly su
ppresse
d.
Therefore, th
e ph
ase
current was just
measured u
p
to
1000
Hz in a
ll cases. Th
e
spe
c
trum of
dc-sid
e
voltage and p
h
a
s
e cu
rre
nt of ac sy
stem 2
(the
c
u
rrent flows
to the PCC point from the
s
y
s
t
em
) are repre
s
e
n
ted in
Figure
4 and
Figure
5. Th
e
1.
6
1.
6
1
1.
62
1.
63
1.
64
1.
65
0.
9
1.
0
1.
1
Ti
m
e
(
s
)
M
a
g
(pu)
ca
s
e
1b
ca
s
e
1
a
1.
6
1.
6
1
1.
62
1.
63
1.
64
1.
65
-1
0
1
Ti
m
e
(
s
)
M
a
g (
p
u)
ca
s
e
1.
a
ca
s
e
1.
b
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TELKOM
NIKA
ISSN:
2302-4
046
Inter-Harm
oni
cs in Voltag
e-Sourced
Con
v
erte
rs
b
a
s
e
d H
i
g
h
Vo
lta
g
e D
i
r
e
c
t
…
(
P
hu
c
h
u
y
N
g
uy
en
)
17
first example
in this ca
se is called
case 1
a
a
s
su
ming that th
e two a
c
sy
stem
s have
no
distortio
n
s. T
he d
c
-side vo
ltage an
d ac
system
2
pha
se
curre
n
t ha
ve quite low l
e
vels. It can
b
e
see
n
from Fi
g.5b, the ac system
2 ph
ase
current i
n
clu
d
e
s
the 5
th
and 7
th
harmo
n
ics. Th
ese
harm
oni
cs a
r
e cau
s
ed
by
dc-ca
p
a
c
itor
ripple
s
wh
en
the t
w
o
ac
systems op
era
t
e at the
sa
me
freque
nci
e
s
(as sho
w
n in (20)).
In the
se
con
d
exampl
e
(calle
d
ca
se
1b), the
a
c
system 1
wa
s assum
ed to
have
a
distortio
n
wit
h
a 10% neg
ative-se
que
n
c
e compo
n
e
n
t at 125 Hz.
As a result,
the dc-side
ha
d
indu
ced i
n
ter-harm
oni
cs
ca
usin
g d
c
-sid
e
voltage to
be
disto
r
ted
(Fig
ure
4a) with
the do
mina
nt
at
175 Hz (Fi
gure 4c). Thi
s
int
e
r-harmoni
c in turn
domin
a
n
tly resulted i
n
the low freq
uen
cy rang
e of
the ac
syste
m
2 a same i
n
ter-harmoni
c to the o
r
igin
at 125
Hz
an
d a ne
w inte
r-ha
rmoni
c
at
225
Hz (Fi
gure 5
c
). The
waveform
s of th
e a
c
system
2
p
hase
curre
n
ts in the
s
e
two
example
s
we
re
similar.
3.2. Case 2
:
DC
Capa
cito
rs Effe
ct Inte
r-
harmo
n
ic Char
acteristi
c of the Sy
stem
In this case, the simul
a
tio
n
model
wa
s simila
rl
y buil
t
as the
ca
se
1, except th
at the ac
system 2
operates
at 60 Hz. As
above mention, the
dc
-side
of
50 Hz-si
de conv
erter will
cont
ain
its own
cha
r
a
c
teri
stic ha
rm
onics, but the
y
are ri
pple
s
to the 60 Hz-side co
nverte
r. These
ripple
s
,
again, are tra
n
sferre
d to the ac-sid
e of this c
onverte
r
to produ
c
e a
non-ch
aracte
ristic h
a
rm
oni
cs
inclu
d
ing i
n
te
r-h
arm
oni
cs.
Ho
wever, th
e
magnitu
de
s
of these inte
r-ha
rmoni
cs a
r
e m
u
ch
smal
ler
than the fund
amental.
As the analy
s
is in the
se
ction 2.5, the
in
ter-h
arm
o
nics on the
ac sy
stem
s coul
d be
originated from the dc
capacitors.
Figure 6 illustrates the effect of
dc capacitors without and
with
third-harmoni
c filters o
n
th
e d
c
-side.
Cl
early, some
l
o
w-f
r
eq
uen
cy
inter-ha
rmo
n
i
cs produ
ce
d
if
third-harmoni
c filters were
not in
stalled.
The simul
a
tio
n
s gave inter-harm
oni
cs were ag
ree
d
wi
th
the an
alytical
re
sults from
(20
)
, which
a
r
e 3
0
Hz, 90 Hz, 210
Hz,
2
7
0 Hz
, 330
Hz
, 390 Hz
, et
c
.
(Figu
r
e 6
b
).
This inte
r-harmonics di
sa
p
peared
with
third
-
ha
rmo
n
ic filters (Fi
g
.6
c), resulted i
n
a
smooth
e
r
current wavefo
rm as shown in Figure 6a.
(
a
) C
u
rr
ent
w
a
vefor
m
(b)
Curre
n
t spe
c
t
r
um of ca
se 2
a
: Without dc
3
rd
filter
(c)
Current s
p
ec
t
r
um of c
a
s
e
2b: With dc
3rd filter
Figure 6. Ca
se 2: the phase
curre
n
t of the ac
system
2 unde
r the e
ffect of dc ca
pacito
rs
1.
6
1.
61
1.
6
2
1.
63
1.
64
1.
65
-1
0
1
Ti
m
e
(
s
)
Ma
g
(p
u
)
ca
s
e
2a
ca
s
e
2b
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ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 13, No. 1, Janua
ry 2015 : 10 – 1
9
18
3.3. Case 3
:
AC Sy
stem 1 Includes Un
balance
d
Ha
rmonic
The
simulatio
n
mod
e
l in thi
s
case i
s
the
model i
n
case 2
with the i
n
stallatio
n
of
dc thi
r
d-
harm
oni
c filters. Th
e inte
r-harm
oni
c lev
e
l co
uld b
e
la
rge
r
if one
en
d ac
syste
m
comp
ri
se
s of
the
backg
rou
nd
harm
oni
cs. In
jecting to the
ac sy
stem 1
a 10% of un
balan
ce
d 2
nd
harmo
nic
(1
00
Hz), the
d
c
-si
de voltag
e a
nd a
c
syste
m
2 p
h
a
s
e
cu
rrent were me
asu
r
ed
for sp
ectra
a
nalyzi
ng.
As re
sult
s, the dc-si
de was induced
a
se
ries
of harm
o
nics wh
ere the 1
st
(50
Hz)
and the 3
rd
(150
Hz) h
a
rm
oni
cs a
r
e th
e d
o
m
inant o
n
e
s
(Figu
r
e
7b
).
They play th
e rol
e
of i
n
ter-ha
rmoni
c
s to
the
60
Hz-side
conve
r
ter. A
nalytically, u
nder th
e
int
e
ra
ction
of
the fund
ame
n
tal switchin
g
comp
one
nt, there
are i
n
te
r-h
arm
oni
cs
at 10 Hz, 90
Hz, 11
0Hz, and 21
0 Hz i
n
low-freq
ue
ncy
rang
e of the ac sy
stem 2 (Figure 8b). In
addition,
there were multip
le inter-harm
onics produ
ced,
becau
se of the intera
ction
of other high
-orde
r
switchi
n
g com
p
on
en
ts.
3.4. Case 4
:
Uns
y
mmetrical AC Sy
stem
In this l
a
st
ca
se, a
si
ngle
p
hase-to
-grou
nd
fault
wa
s i
n
vestigate
d
i
n
stea
d of
ba
ckgroun
d
harm
oni
c in the ca
se 3.
A fault occu
rred on th
e a
c
system
1 resulting
inter-h
a
r
moni
cs to be
pro
d
u
c
ed i
n
the dc-
link
and
the
ac
system
2. Figu
re
7
c
sh
ows t
he simulatio
n
re
sult
in
corre
s
po
ndin
g
to the
methodol
ogi
cal analy
s
is i
n
se
ction
2.6
with 10
0
Hz
ripple
on th
e
dc-sid
e. Con
s
eq
uently, there
were two in
d
u
ce
d inter-ha
rmoni
cs with
freque
nci
e
s a
t
40 Hz a
nd
160 Hz (Fi
g
u
r
e 8
c
). Nota
b
l
y,
the 40 Hz inter-harmoni
c i
s
t
he neg
ative-sequ
en
ce
comp
one
nt smaller tha
n
the fundam
en
tal
one. If a seri
es re
so
nan
ce
at this frequ
ency o
c
curs, a mode
st inter-h
arm
o
ni
c voltage is
see
m
ed
dra
s
tically to
amplify the inter-harmoni
c current, da
maging th
e rotating ma
chi
n
e conne
cte
d
to
the ac sy
ste
m
2.
Although the
dc-sid
e volta
ge in the
ca
se 3 wa
s la
rge
l
y distorted i
n
comp
ari
s
on
with the
ca
se 4 (Fi
gure 7a), the a
c
system 2 p
h
a
s
e curr
ent
s in
bot
h ca
se
s w
e
re si
milar
(Fi
g
ure 8
a
).
(a) Voltage
wave
form
(b)
Voltage sp
ect
r
um of ca
se 3
(c)
Voltage sp
ect
r
um of ca
se 4
Figure 7. Dc-side voltag
e whe
n
the ac
system
1 (50 Hz) ha
s unbala
n
ced
2
nd
harmoni
c
(ca
s
e
3), and un
sy
mmetrical fau
l
t (ca
s
e 4).
(
a
) C
u
rr
ent
w
a
vefor
m
(b)
Cur
r
e
n
t
spe
c
t
r
um of
ca
se 3
(c
)
Cur
r
e
n
t
spe
c
t
r
um of
ca
se 4
Figure 8. The pha
se curre
n
t of the ac system
2
w
h
en
th
e
ac
s
y
s
t
em 1
(
5
0
H
z
)
h
a
s
unbal
a
n
c
ed 2
nd
harmoni
c (ca
s
e 3), an
d
unsymm
e
trical fault (ca
s
e
4).
4. Conclusio
n
The
sp
ace ve
ctor re
presen
tation
of
V
S
C’
s
swit
chin
g f
u
nct
i
on
s i
s
a s
t
raightforward tool
to
1.
6
1.
6
5
1.
7
1.
75
1.
8
0.
6
0.
7
0.
8
0.
9
Ti
m
e
(
s
)
M
a
g (
pu)
ca
s
e
3
ca
se 4
1.
6
1.
6
5
1.
7
1.
75
1.
8
-1
0
1
Ti
m
e
(
s
)
M
a
g
(pu)
ca
s
e
3
ca
se 4
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
Inter-Harm
oni
cs in Voltag
e-Sourced
Con
v
erte
rs
ba
sed
High Voltage
Dire
ct… (Ph
u
ch
uy
Ngu
y
e
n
)
19
study harm
o
nic interactio
n. From that, the or
igin of inter-ha
r
m
onics in VSC-b
ased HV
DC
system
s was
investigate
d
and cl
assified
as:
(1)
Re
sulting fro
m
the cha
r
a
c
teristi
c
of
each conve
r
ter in
asynchro
nou
s co
nne
ction;
(2)
Re
sulting fro
m
a distortin
g
frequen
cy;
(3)
Re
sulting fro
m
unsymmet
r
ical fault or u
nbala
n
ce;
In all ca
se
s,
there
wa
s a
seri
es
of inte
r-h
arm
oni
cs
prod
uced, wh
ich i
s
be
cau
s
e of the
intera
ction of
both funda
mental an
d carri
er
si
de
ba
nd (hi
gh-orde
r)
swit
chin
g comp
one
nts.
For
confirmation,
the simul
a
tio
n
model
s
we
re set up to i
m
pleme
n
t, and giving
re
sults ag
ree
d
with
the theoreti
c
a
l
analyse
s
. In corre
s
po
ndin
g
to the resu
lts, the effect of dc cap
a
cito
rs is si
gnifican
t
in raisi
ng a serie
s
of low-freque
ncy inter-ha
rmoni
cs.
It has to put attention to
the inter-harm
onics who
s
e freque
nci
e
s are lo
we
r than the
fundame
n
tal, espe
cially if they are n
egativ
e-seq
u
ence com
p
o
nents. Th
ese
inter-h
arm
o
nics
coul
d se
riou
sl
y damage the
rotating ma
chine
s
co
nne
cted to the system.
Referen
ces
[1]
P
Jiupin
g
, R Nuqu
i, K Srivastava, et al.
AC
Grid w
i
th Embedd
ed VSC-H
VDC for Secure and Efficien
t
Pow
e
r Deliver
y
. Proceedin
g
s
of
the IEEE
Energ
y
20
30
C
onfer
ence (E
NERGY
200
8)
,
Atlanta, GA,
200
8; 1-6
[2]
Stamatios K.
Kartala
p
o
u
los
et al. Pulse W
i
dth
Modul
atio
n
for Po
w
e
r Co
nverters. Ne
w
Jerse
y
: IEEE
Press. 2003.
[3]
Lih
ua Hu, R
o
b
e
rt
Y
a
cami
ni. Harmon
i
c
T
r
an
sfer through
C
onverters a
nd
HVDC li
nks.
IEEE T
r
ans.
Power Electronics
. 1992; 7(3):
514–
52
4
[4]
Y
i
n
g
Jian
g,
Ake Ekstrom. Ge
nera
l
Anal
ys
is
of Harmonic
T
r
ansfer throu
g
h
Convert
e
rs.
IEEE T
r
ans.
Power Electronics
. 1997; 1
2
(2
): 287–2
93
[5] EW
Gunther
.
Inter
-
harmonics
in power system
s
. Proce
e
d
i
n
g
s of the IEEE
Po
w
e
r En
gi
ne
erin
g Soci
et
y
Summer Meeti
ng, V
anco
u
ver
,
BC. 2001; 2: 8
13-8
17.
[6]
L
Hu, R
Y
a
camini.
Calc
ul
ati
on of har
mo
nic
s
and inte
r
-
har
mo
nics i
n
HVD
C
sche
m
es w
i
th low
dc-sid
e
impe
danc
e
. Procee
din
g
s C of
IEE Generatio
n,
T
r
ans
missio
n
and D
i
stributi
on. 199
3; 140:
469-
476.
[7]
Lia
n
g
x
i
a
n
g
T
ang, Boon-T
eek Ooi.
Converter
Noninte
g
ral H
a
rmonics fro
m
AC netw
o
rk Resonati
ng w
i
th
DC Netw
ork
. Procee
din
g
s of the IEEE Indust
r
y
App
licat
i
ons Soc.
Confere
n
c
e.
2001; 4: 21
86-2
192.
[8]
Math HJ, Bolle
n, Kai
Y
ang. H
a
rmoni
c as
pec
ts of
w
i
nd po
wer integrati
on.
J. Mod. Power
Syst. Clean
Energy
. 20
13;
1(1): 14-2
1
.
[9]
Amirnas
er
Y
a
z
dan
i, Reza Ira
v
ani. V
o
ltag
e-
Source
d Conv
erters in Po
w
e
r S
y
stems.Ne
w
Jerse
y
: IEEE
Press. 2010.
[10]
Guibi
n
Z
han
g,
Z
heng
Xu, Gu
angz
hu W
ang.
Contro
l Strate
gy for Unsy
mmetric
a
l Op
era
t
ion of HV
DC-
VSC base
d
on
the improve
d
inst
anta
n
e
ous
reactive p
o
w
e
r theory
. Proceedings of the IEEE
AC-DC
Po
w
e
r
T
r
ansmi
ssion i
n
ternati
o
nal co
nfere
n
ce
, Londo
n, UK. 200
1; 262-
267
Evaluation Warning : The document was created with Spire.PDF for Python.