TELKOM
NIKA Indonesia
n
Journal of
Electrical En
gineering
Vol.12, No.4, April 201
4, pp. 3193 ~ 3
1
9
9
DOI: http://dx.doi.org/10.11591/telkomni
ka.v12i4.4930
3193
Re
cei
v
ed Se
ptem
ber 21, 2013; Revi
se
d No
vem
ber
20, 2013; Accepted Decem
ber 9, 201
3
A Kind of Discrete Variable Frequency Heavy-
Load
Soft Sta
r
t System
Xiao Yi-ping
Schoo
l of Elect
r
ical a
nd Electr
onic En
gin
eer
i
ng, Hub
e
i U
n
iv
ersit
y
of T
e
chn
o
lo
g
y
, W
u
h
an,
Chin
a
email: yp
_
x
ia
o
201
3@1
63.co
m
A
b
st
ra
ct
A kind of discr
ete varia
b
l
e
freque
ncy he
avy-l
oad so
ft start system w
a
s des
ign
ed in
order t
o
real
i
z
e
heavy-
loa
d
s
o
ft starting
of
mo
tor. It consiste
d of v
a
ria
b
le
re
actance
co
nve
r
ter, discrete
v
a
ria
b
le
frequ
en
cy
converter
and
controller. The
system
struct
ure was descri
bed in detail and
the pr
in
ciple of
discrete variabl
e
freque
ncy h
e
a
vy-loa
d
soft starting w
a
s
an
a
l
y
z
e
d
. Als
o
the
mode
l of th
e s
ystem w
a
s
ma
de a
nd s
i
mul
a
t
i
o
n
of the system w
a
s done. The
simu
latio
n
res
u
lts prove
d
tha
t
the system c
an not on
ly start motor smoot
hly,
but als
o
i
n
cre
a
s
e the
motor s
t
art torque
gre
a
tly, thus
h
eav
y loa
d
soft-sta
r
ting of
motor
can b
e
re
ali
z
e
d
perfectly. In
addition, the ex
perim
ent of t
h
e system
was
done. The ex
perim
ent res
u
lt
s prov
ed that
the
simulati
on w
a
s
correct a
nd t
he d
e
si
gne
d
d
i
screte va
r
i
a
b
l
e
freq
uency
h
eavy-l
oad
soft start system
ca
n
reali
z
e
he
avy-l
oad soft start of motor.
Ke
y
w
ords
:
he
avy loa
d
, discr
ete varia
b
le frequency, soft start
Copy
right
©
2014 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
AC motor n
e
eds to be
soft-starte
d to le
ssen the
curre
n
t impa
ct, voltage drop an
d
damag
e, as
well a
s
save
energy and
redu
ce
co
st. There are m
any soft sta
r
t ways fo
r wo
und
rotor m
o
tor
s
su
ch a
s
Y/
ᇞ
start, autoformer redu
ced
-
voltage sta
r
ting, stator
re
sistan
ce sta
r
ti
ng,
seri
es-con
ne
cted thyristo
r voltage-dro
p
starting
[1
-3]. These
sof
t
start metho
d
s are aime
d
to
start
motor softly by red
u
c
ing
sta
r
t vol
t
age
of
mot
o
r .
Ho
weve
r, motor sta
r
ting to
rqu
e
co
uld
redu
ce
sha
r
pl
y whe
n
stator voltage
re
du
ced
[4, 5
]. T
h
erefo
r
e, fo
r it
coul
d n
o
t p
r
o
v
ide big
en
ou
gh
starting to
rq
u
e
, redu
cin
g
-v
oltage
soft st
art metho
d
could n
o
t be fit for heavy load
start a
nd
coul
d be fit
for no-lo
ad st
art and light
-l
oad sta
r
t.
In this pa
pe
r, a kin
d
of di
screte va
riabl
e freq
uen
cy
heavy-loa
d
soft start sy
st
em was
prop
osed. It con
s
i
s
ted of
variable
rea
c
tance
co
nv
erter, discrete
variable f
r
eq
uen
cy co
nverter
and
cont
rolle
r. It used
the
spe
c
ial
structure of
va
riab
le re
acta
nce
conve
r
ter
an
d co
ntroll
ed t
he
high voltag
e
circuit with
lo
w voltage
circuit. By
controlling
curre
n
t in the lo
w voltage
circuit, the
curre
n
t in the
high voltage circuit ca
n be
contro
ll
ed. Redu
cing stato
r
curre
n
t frequen
cy of motor
in the
high
vo
ltage
circuit, t
he
start to
rq
u
e
can
be
rai
s
ed a
nd
sta
r
t
curre
n
t can
b
e
d
r
op
ped,
a
n
d
then heavy lo
ad soft sta
r
t of high-voltage
motor ca
n be
realized.
2. Proposed
Appro
ach
2.1. Structu
r
e Design o
f
Discre
t
e Vari
able Frequ
e
nc
y
Hea
v
y
-
load Soft Sta
r
t Sy
stem
M
disc
r
e
t
e
va
r
i
a
b
l
e
f
r
e
que
nc
y
c
onv
e
r
t
e
r
c
ont
rol
l
e
r
R
T
S
va
r
i
a
b
l
e
r
eactan
ce
c
onve
r
t
e
r
Figure 1.
The
Structure Dia
g
ram of the Discrete
Vari
ab
le Freq
uen
cy Heavy-lo
ad S
o
ft Start
Sys
t
em
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 4, April 2014: 3193 – 3
199
3194
The stru
cture
diag
ram of discrete
varia
b
le
fre
que
ncy heavy-loa
d
soft
start
system i
s
sho
w
n in Fig
u
re 1. The sy
stem mainly consi
s
ts of
vari
able re
acta
nce conve
r
ter, d
i
screte vari
ab
le
freque
ncy co
nverter a
nd controlle
r [6-8]
.
The p
r
in
ciple
of variabl
e
rea
c
tan
c
e
co
nverter
wa
s
descri
bed i
n
the refe
ren
c
e [9] in
detail.
Co
ntro
ller con
s
i
s
ts o
f
stat
or
cu
rre
n
t dete
c
t ci
rcuit, control
circuit, a
nd d
r
iv
e ci
rcuit. Co
ntrol
circuit ad
opts microchip 8
0
C1
96KC.
Di
screte va
ri
abl
e frequ
en
cy converte
r is m
a
inly made u
p
of
three p
a
irs o
f
reverse pa
rallel thyristo
r. RC seri
e
s
circuits are conne
cted with
thyristors
i
n
parall
e
l in order to protect
the thyristors thro
ugh the
cache fun
c
tion of cap
a
cit
ance C. Di
scret
e
variable frequ
ency convert
e
r structu
r
e i
s
sho
w
n in Fig
u
re 2 a
s
follo
ws:
Figure 2. The
Structure Dia
g
ram of Di
screte Variabl
e Freq
uen
cy Converte
r
2.2. Principle of the Sy
stem
Whe
n
motor
start
s
, stator
start cu
rrent I
st
and start torque T
st
ca
n be expre
ssed into
expre
ssi
on (1
) and exp
r
e
s
sion (2
) re
spe
c
tively [10, 11].
2
2
1
2
2
1
1
)
(
)
(
x
x
r
r
U
I
st
(1)
2
2
1
2
2
1
2
2
1
1
1
)
(
)
(
2
x
x
r
r
r
U
f
p
m
T
st
(2)
In expre
ssi
o
n
(1
) an
d ex
pre
ssi
on
(2),
stator
re
sist
ance is
1
r
、
sta
t
or win
d
ing l
eakage
impeda
nce i
s
1
x
、
equival
ent
roto
r
re
sista
n
ce
after con
v
erting i
s
2
r
、
rotor windi
ng equivalent
leakage
impe
dan
ce after converting
is
2
x
、
the fre
que
n
c
y of
stator current
or vol
t
age i
s
1
f
、
the pha
se n
u
mbe
r
of stator windi
ng is
1
m
、
numbe
r of pole-pai
rs i
s
p
、
stator volta
ge is
1
U
.
Acco
rdi
ng to
the expre
s
sio
n
(1), it ca
n b
e
see
n
that stator
start current is p
r
op
ortional
to stator sta
r
t voltage. A
s
stator volt
age d
e
cr
e
a
ses,
the stat
or star
t cu
rrent
de
crea
ses.
Mean
while,
a
c
cordi
n
g
to t
he exp
r
e
s
sio
n
(2),
stator
start to
rqu
e
i
s
p
r
o
portio
n
a
l
to the
squa
re of
the stator vo
ltage and is
inversely pro
portion
al to
the frequ
en
cy of stator
cu
rre
nt or stat
or
voltage. Whe
n
stator volta
ge decrea
s
e
s
, stator
sta
r
t torque de
cre
a
se
s sharply, which may lead
to motor n
o
t
being
sta
r
ted.
But if
redu
ci
ng
the
freque
ncy of the stator curre
n
t (o
r voltage) to 1/k
(k is a
natural num
be
r)
o
f
the
po
we
r
freque
ncy, th
e sta
r
t torqu
e
can i
n
crea
se
by k time
s
comp
ared wi
th directly voltage-re
du
ce
d starti
ng, thus the sta
r
t torque can
be enhan
ced
greatly.
Controlle
r
co
ntrols the
trig
gerin
g time
a
nd trig
ge
ring
angle
of thyri
s
tors i
n
the
d
i
screte
variable freq
uen
cy conve
r
ter whic
h conne
cted in
serie
s
with
second
ary side of vari
able
rea
c
tan
c
e
co
nverter i
n
o
r
der to
ch
ang
e trigg
e
r fr
eq
uen
cy of thyristors. The
tri
gger freq
uen
cy
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
A Kind of Discrete Va
riabl
e Freq
uen
cy Hea
v
y-L
oad
Soft Start System
(Xiao Yi-ping)
3195
can
be in
cre
a
se
d ste
p
by
step from 1/
k of t
he p
o
wer fre
que
ncy
to the po
we
r
freque
ncy. T
hus
the freque
ncy
and amplitud
e of current in
the sec
ond
ary side of the variable
rea
c
t
ance co
nvert
e
r
can b
e
chan
ged. Co
nseq
uently, the freque
ncy an
d
am
plitude of
current in th
e prima
r
y sid
e
of
the varia
b
le
reacta
nce con
v
erter
can
al
so b
e
cha
n
g
ed a
c
cordingl
y due to th
e
elect
r
oma
g
n
e
tic
indu
ction. On
ce the
curre
n
t
frequen
cy o
f
stator re
du
ced, the start t
o
rqu
e
of the motor would
be
raised an
d di
screte vari
abl
e freque
ncy soft start with heavy load can be re
alize
d
.
Take
4
-
divisi
on fre
que
ncy
for exam
ple,
trigge
r the
th
yristors
in th
e time of th
e
sha
ded
part of the followin
g
Figu
re 3. That is to say, tr
igger the thyrist
o
rs in th
e pe
riod of the first
positive
half-wave, the
se
con
d
p
o
sitive
half-wave,
t
he third
nega
tive half-wave, and
the fo
urth
negative
half-wave,
cu
rre
n
t (o
r volta
ge)
wh
ose
freque
ncy i
s
1
2
.5Hz
can
b
e
form
ed,
which
calle
d 4-divi
si
on freq
uen
cy
current (volt
age). Th
e pr
i
n
cipl
e of othe
r divisio
n
freq
uen
cy is simil
a
r
to the 4
-
divisi
on fre
que
ncy.
The
sche
mat
i
c di
agram
of
4-divisi
on f
r
e
quen
cy i
s
sh
own
in Fi
gu
re
3
as
follows
.
Figure 3. The
Schemati
c
Diagra
m
of 4-di
vision Frequ
e
n
cy
The po
wer freque
ncy ca
n be divided into different levels of frequency wh
ose frequ
en
cy
value is 1/k o
f
the powe
r
freque
ncy valu
e. The re
latio
n
shi
p
betwee
n
the power f
r
equ
en
cy value
and the
s
e di
fferent levels
of freque
ncy
value
s
ca
n be expresse
d into expre
ssi
on (3
)
as follo
ws (k i
s
a natu
r
al nu
mber).
k
s
*
(3)
Assu
ming th
a
t
initial A-pha
se p
h
a
s
e a
n
g
l
e of the p
o
wer fre
que
ncy i
s
zero, pha
se
angle
s
of B pha
se
a
nd C ph
ase a
r
e
n
t
2
3
2
and
n
t
2
3
4
(n i
s
integer). So if
initial A-
pha
se ph
ase
angle of k-di
vision freq
ue
ncy is a
s
sum
ed as
zero, phase angle
s
of B phase a
nd
C pha
se are
k
n
t
s
2
3
2
and
k
n
t
s
2
3
4
res
p
ectively.
Appro
p
riate i
n
itial pha
se
angle
com
b
i
nation
mu
st be
choo
sed to
maximize positive
pha
se-se
que
nce
cu
rrent o
f
division freq
uen
cy. As a
result, po
sitive maximum t
o
rqu
e
could
be
cre
a
ted. If
k i
s
e
qual
to
(
1+3
n
), th
at is to sa
y, k is
equal
is 1, 4,
7, 10,
13,
1
6
……., divisi
on
freque
ncy
cu
rre
nt is th
ree
-
pha
se
symm
etric
po
sitive seq
uen
ce
cu
rrent, an
d po
sitive sequ
en
ce
comp
one
nt is maximum value. And its initial phas
e an
gle of three p
hase are 0
°
, 120° a
nd 24
0
°
.
If k is eq
ual t
o
(1
+3n
)
/2, th
at is to say, k is eq
ual is
2, 5, 8, 11, 14,
17……., divi
sion frequ
ency
curre
n
t is three-p
h
a
s
e
symmetric
neg
ative sequ
en
ce
current. If k is e
qual to
3, 6, 9, 12, 15,
18……., division frequ
en
cy cu
rre
nt is three-pha
se
asy
mmet
r
i
c
pha
se s
equ
e
n
ce
cu
rre
nt
.
For
three
-
ph
ase
asymm
e
tric pha
se
seq
uen
ce
cu
rre
n
t and
thre
e-ph
ase
symmetric ne
g
a
tive
seq
uen
ce
cu
rrent, initial ph
ase
angle
mu
st be
combi
n
ed to maximi
ze p
o
sitive p
hase-seq
uen
ce
comp
one
nt.
Table 1. Th
re
e Phase
Optimal Initial Phase Angl
e Co
mbination of
Different Lev
els of Fre
que
ncy
K
Phase se
que
nc
e
f(H
Z)
Grou
p1
Grou
p2
Grou
p3
2 negative
sequen
ce
25
(0°,60
°,210°
)
(0°,150
°,210°
)
(0°,240
°,120°
)
4 positive
sequence
12.5
(0°,120
°,240°
)
\
\
7 positive
sequence
7.14
(0°,120
°,240°
)
\
\
13 positive
sequence
3.85
(0°,120
°,240°
)
\
\
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 4, April 2014: 3193 – 3
199
3196
Acco
rdi
ng to
co
rrespon
ding th
eory [
12-1
6
], thre
e
pha
se
opti
m
al initial
ph
ase
an
gle
combi
nation
of different levels of fr
eque
ncy is sho
w
n
in Table 1 a
s
follows.
As
cont
rolle
r chang
ed
freque
ncy, fre
quen
cy
wa
s
often re
qui
re
d to b
e
p
r
op
o
r
tional to
voltage, nam
ely, the ratio betwe
en fre
q
uen
cy and
vo
ltage wa
s oft
en re
quired to be a con
s
tant.
Con
s
id
erin
g the co
mpe
n
sa
tion of voltage, trigger
ang
les of the thyristors corre
s
p
ondin
g
to ea
ch
corre
s
p
ondin
g
level divisio
n
freque
ncy can be
de
du
ce
d as sho
w
n in
Table 2 as fo
llows.
Table 2. Trig
ger Angl
es of
the Thyristo
rs Co
rrespon
d
i
ng to each Corres
pon
ding Level
Divisio
n
Freq
uen
cy
f1(HZ
)
25 12.5
7.14
5
U1
(V)
1
1
0
60 40 30
T
r
igger
angle
75°
90°
96°
100°
3. Simulation and Analy
s
is
Usi
ng Po
we
r System Blo
c
kset i
n
Matl
ab/Simulin
k,
the di
screte
variabl
e f
r
eque
ncy
system can b
e
simul
a
ted. The
si
mulatio
n
model of
di
screte va
riabl
e frequ
en
cy system i
s
sho
w
n
in Figu
re 4 [
17]. The mot
o
r’s
rate
d po
wer i
s
1
1
kW,
stator
rated
voltage is
38
0V, stator
ra
ted
curre
n
t is 1
6
A, and fre
q
uen
cy is 5
0
H
z. T
he mot
o
r’s pole
pai
rs i
s
2. Va
ri
able rea
c
tan
c
e
conve
r
ter’
s ra
ted power is
10kW. Its primary windi
n
g
’s ph
ase voltage is 220V,
resi
stan
ce R is
0.002
Ω
, an
d rea
c
tan
c
e X=0.01H. Its se
con
dary wi
nd
ing’s p
h
a
s
e voltage is 5
5
V, and resi
stan
ce
R is 0.0
005
1
Ω
, rea
c
tan
c
e
X=0.002
H. T
he sim
u
lation
algorithm i
s
ode2
3tb. The
simulatio
n
m
odel
of discrete va
riable frequ
en
cy system i
s
sho
w
n in Fig
u
re 4 a
s
follo
ws.
v
a
r
i
ab
l
e
r
e
act
a
n
c
e con
v
er
t
e
r
di
s
c
re
t
e
va
r
i
a
b
l
e
f
r
e
que
nc
y c
o
nv
e
r
t
e
r
c
o
n
t
ro
lle
r
Figure 4.
Simulation Mod
e
l
of Discrete V
a
riabl
e Fre
q
u
ency System
Acco
rdi
ng to
the simul
a
tion mod
e
l o
f
discrete v
a
riabl
e freq
u
ency
system
, using
hiera
r
chi
c
al start
mo
de like
1/7f
1/4f
1/2f
f (f
is po
wer f
r
equ
en
cy
), d
i
sc
rete v
a
ri
a
b
le
freque
ncy
cu
rre
nt wave
a
nd sta
r
t torqu
e
wave
ar
e shown in Fi
gu
re 5.
While
d
r
op
-voltage
soft
start torq
ue wave is sh
own in Figure 6.
As sho
w
n in
Figure 5, start frequen
cy varie
s
from 1/
7f (f is powe
r
frequen
cy) to 1/4f
,
then from 1/4
f
to 1/2f, the
n
from 1/2f
to f.
Start current maximu
m value is about 2 times the
rated cu
rrent.
Com
pared Figure
5 and
Figure 6, it
can
be
see
n
that start to
rque
of di
screte
variable f
r
eq
uen
cy syste
m
is n
early 3
times bi
gge
r than that of
drop
-voltag
e
soft sta
r
t syst
em.
Therefore, a
con
c
lu
sio
n
ca
n be d
r
a
w
n t
hat discre
te variabl
e freq
u
ency
start sy
stem can
real
ize
soft start an
d has
so large
start torq
ue that it can ca
rry heavy load.
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
A Kind of Discrete Va
riabl
e Freq
uen
cy Hea
v
y-L
oad
Soft Start System
(Xiao Yi-ping)
3197
i/A
0
50
-5
0
24
6
8
1
0
0
-1
0
0
10
0
t/
s
(a) Simulation wave of c
u
rrent
02
4
6
8
10
t/
s
0
10
0
-1
0
0
20
0
30
0
40
0
-2
0
0
T/
N
.
m
(b) Simulation wave of s
t
art torque
Figure 5.
Simulation Wave of (a) di
screte
variable fre
q
uen
cy curre
n
t and (b
) sta
r
t torque
24
6
8
1
0
0
10
0
-1
0
0
20
0
30
0
0
T/
N.
m
t/
s
Figure 6. Simulation Wave of Drop
-volta
ge Soft Start
Torq
ue
4. Experiment
Discrete vari
able fre
que
ncy start syste
m
experim
ent
was
don
e ba
sed o
n
the si
mulation
of the syste
m
above. Th
e start moto
r is Y90S
-4 a
s
ynchro
nou
s
motor who
s
e
rated po
we
r was
1.1 KW, stator rate
d voltage wa
s 38
0V
and stato
r
ra
ted cu
rre
nt was 2.7A. Synchrono
us
spe
e
d
wa
s 1500
r/mi
n. The rated
start torq
ue was 7
N
.M. Va
riable rea
c
tan
c
e conve
r
ter’
s rated power
wa
s 11
kW. S
t
art mode a
d
opted 5 level
s
sta
r
t. The 5 levels were
1/10f, 1/7f,
1/4f, 1/2f and f.
Start current
wave of discrete variable fr
eque
ncy sta
r
t system is
sh
own in Fig
u
re
7.
t/
s
i/
A
0
5
-5
10
250
m
s
/
u
n
i
t
0
(a) 5 level
s
st
art cu
rrent wa
ve
0
5A
/
uni
t
t/
s
i/
A
1
s
/
uni
t
(b) di
screte v
a
riabl
e freq
ue
ncy soft sta
r
t
cur
r
e
n
t
wav
e
Figure 7. Start current wav
e
of di
screte
variable frequ
ency sta
r
t system
Figure 7(a
)
sho
w
s 5 levels sta
r
t cu
rrent
clea
rly. The cu
rrent freque
ncy vari
es from
1/10f to
1/7f, then
from
1
/
7f to 1/4f, t
hen f
r
om
1/4
f
to 1/2f, fin
a
lly from
1/2
f
to the
po
wer
freque
ncy f. From Fi
gure
7(b
)
, it can b
e
see
n
that
start current
is abo
ut 2.5 times the rated
cur
r
e
n
t
.
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 4, April 2014: 3193 – 3
199
3198
Load
wa
s
magneti
c
p
o
w
de
r b
r
a
k
e.
The m
agn
etic p
o
wder b
r
a
k
e’
s maxim
u
m exciting
curre
n
t wa
s
1.0A and it
s
rated to
rqu
e
wa
s 10
0N.M
.
The m
agn
etic p
o
wder b
r
ake’ to
rq
ue
was
nearly p
r
op
ortional to the exciting curre
n
t. Hence,
controllin
g the
bra
k
e’s
excit
i
ng cu
rrent can
control th
e
load to
rq
ue.
The
rel
a
tio
n
shi
p
bet
wee
n
torq
ue
and
exciting
cu
rrent is
sh
own
in
Figure 8.
0.
2
0
.
4
0.
6
0
.
8
1
ex
cit
i
ng
curre
nt
£¨
A£©
20
40
60
80
10
0
tor
q
u
e
(N
.
M
)
Figure 8. The
Relation
ship
betwe
en To
rq
ue and Exciti
ng Cu
rrent
Assu
ming tha
t
the magnetic powde
r
bra
k
e’
s exciting
curre
n
t is
a
i
、
motor
stato
r
current
is
s
i
、
motor run c
u
rrent is
r
i
. Measuri
ng
data of curre
n
t is sho
w
n i
n
Table 3.
Table 3. Mea
s
uri
ng Data o
f
Current
(A)
(A)
(A)
0(No load
)
6.3
→
2.04
2.04
0.1 7.0
→
2.65
2.65
Acco
rdi
ng to
Figure 7, it can
be
se
en t
hat wh
en ex
citing cu
rrent
as 0.1, the l
o
ad torq
ue
wa
s abo
ut 7
N
.M, almost
rea
c
hin
g
mot
o
r rate
d torq
ue. That is t
o
say, the m
o
tor sta
r
ted
with
heavy load. Acco
rdi
ng to
the Table 3, t
he sta
r
t cu
rre
nt varied fro
m
7.0A to 2.65A, its maximum
value was m
e
rely ab
out
2.6 times th
e rated
cu
rr
ent. This
discrete
varia
b
l
e
frequ
en
cy start
system
can
start motor
softly with heavy load.
5. Conclusio
n
A discrete variable fre
que
ncy start sy
stem
wa
s studi
ed. It can rea
lize discrete variabl
e
freque
ncy
so
ft start with
heavy load. I
t
controlled
the stator sta
r
t
cu
rrent
by
co
ntrollin
g
t
he
discrete va
ria
b
le freq
uen
cy
conve
r
ter. B
y
controlli
ng t
he trigg
e
ri
ng
time and tri
g
gerin
g an
gle
o
f
thyristors in d
i
screte va
riab
le frequ
en
cy conve
r
te
r
co
n
necte
d in se
ries
with the
se
con
dary
si
de
of variable reacta
nce co
nverter,
the
power fre
que
ncy ca
n be
divided into
different leve
ls of
freque
ncy. T
hus the fre
q
uen
cy and a
m
plitude of current
in the primary si
d
e
of the variable
rea
c
tan
c
e
co
nverter
ca
n b
e
ch
ang
ed, a
nd the
start t
o
rqu
e
of the
motor
woul
d
be raise
d
. So
, the
discrete
varia
b
le freq
uen
cy
start
system
can
sta
r
t mo
tor softly with heavy load.
In addition, t
he
system
co
uld
be mo
re
saf
e
ty beca
u
se i
t
controll
ed
motor in
high
voltage
circu
i
t by controlli
ng
discrete va
ria
b
le frequ
en
cy converte
r in l
o
w voltage
circuit.
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ces
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engi
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uz G, Cadirc
i I, Ermis M, Barlak C. Soft st
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ductio
n
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t
w
i
t
h
min
i
mize
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starting torq
u
e
pu
lsatio
ns.
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1; 37(5)
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133
4–
134
7.
a
ii
s
i
r
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
A Kind of Discrete Va
riabl
e Freq
uen
cy Hea
v
y-L
oad
Soft Start System
(Xiao Yi-ping)
3199
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Evaluation Warning : The document was created with Spire.PDF for Python.