A new structure of serial hybrid active power filter for

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ISSN 1009 3095 Journal of ,Z17ejiang University(SCIENCE) V. 1, No. 4, P. 394 - 397, Oct. - Dec., 2(XX)
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394
A NEW STRUCTURE OF SERIAL HYBRID ACTIVE POWER FILTER
FOR HIGH POWER APPLICATION"
CHEN G u o - z h u ( [ ~ , l ~ ) t , LU Z h e n g - y u ( ~ - ~ - ) ,
QLAN Z h a o - m i n g ( $ ~ , ~ ] )
( Electrical Institute of Zhejiang University, Hangzhou, 310027, China)
"I"E-mail: [email protected]
Received Aug.28, 1999; revision accepted Apr. 15,2000
Abstract:
This paper proposes a new structure of serial hybrid active power filter which can reduce the
power rating of the active power filter dramatically, and has good performancefor ham~nic suppression. The
principle and designing rides are analyzed, rllae proposed structure is rational and feasible for high kVA applications. Simulation rexsultsare presented too.
Key words: activepower filter, harmonics, power conditioning, power quality
Document code: A
CLC ntmfl~r: TM714
INTRODUCTION
To cope with the more and more serious harmonic problems mainly caused by power electronic equipment application, various kinds of
active filters have been proposed and put into
field applications recently. Among them, a Serial Hybrid Active Power Filter ( S H A P F ) as
shown in Fig. 1 (exclude the dotted box) is particularly attractive due to its low cost, good performance, multi-function and small rating serial
active power filter ( A P F , typically 5 % of the
l o a d ) . It presents a resistance k to harmonic
current and a low resistance to fundamental component (Chen et a l . , 1998; Peng et al. , 1988)
However, it is clear that when the system
power rating is high, the Voltage Source Inverter
( V S I ) , the APF, has to deliver not only the
harmonic power but certain amount of fundamental power components too. This causes high demand for a large power rating of VSI. It is difficult to protect the APF inverter too due to its serial structure. These actually limit the SHAPF
application. }'or this reason, only one power
system application in U. S. A has been reported
( Bhattacharga et al. , 1995).
PRINCIPLES AND ANALYSIS
with notch impedance character is proposed
(Fig. 1 ) for preventing current coupled from the
main circuit from impacting on the VSI. By detailed design, it acts as a sink for the fundamental current and voltage from the main side and
the APF inverter respectively.
Where, PPF1 is the fundamental frequency
tuned L - C branch proposed by this paper; PF
is a set of passive filters, such as 5th, 7th and
so on, and a high pass one; Vc, Vr are the output voltage vectors of the APF and VSI respectively; Z r is the equivalent impedance of VSI including a low pass filter. In Fig. 1 hereafter V,
I , Z represent voltage, current and impedance
of the branches ; Subscripts S , L , F , r and p
represent the branches source, load, PF, VSI
and PPF1 respectively.
1. Design considerafiorts
For the aim that most fundamental current
coupled from the main side sink into PPF1 and
without causing high fundamental voltage or increasing harmonic current supplied by the VSI,
it has to comply with the following conditions:
I Zp(co0) I = R < : I Zr(CO0) I
I /p(CO0) " Zp(co0) I"--~ Lsl x COo x ls(COo)/n---"O
I Zp(CO h ) I::~-I JCOh X Lsl + Zl(COh) 13~1 Zr(COh) I
(1)
A fundamental frequency tuned L-C filter
9 Projectsupportedby DELTA~ience. Technologyand FMucationI~velopmentFoundationfor PowerEl~tronicsof China.
A NEW STRUCTURE OF SERIAL HYBRID ACTIVE POWER FILTER
395
[ Vc ( (oo ) = I , ( (oo ) " j(Oo L2 + I t ( ( o 0 ) " j(oo M
Source
Vs
ls
Vc
zp((oo)
E
/ = I t ( ( o 0 ) " j(ooLl + I s ( ( o o ) " j(ooM
tlt(a~o) + Ip((oo) = /r((o0) ~ 0
(3)
VSI
Z,
t'-"
v~
""l
Z,
Nolinar
load
Hg.
Zr
Proposed serial hybrid active power filter
(SHAPF) for high power application
Where (o0, cob are fundamental and harmonic
frequencies; Zp ( o-,0 ) is impedance of the PPF1
tuned L - C branch ; n is the transformer ratio;
R is the equivalent resistance of the tuned
PPF1; Lsl is the primary leakage induc "tance of
the transformer. Z1 (cob) is the equivalent impedance to harmonics of the transformer converted from the main side. Here I j(oh x Lsl I>>1
ZI ((oh) I is usually tenable for the main source
and the PF.
By using Equation ( 1 ) , the current of the
inverter (VSI) can be calculated as:
I~ = I , ( ( o 0) + / r ( C O h )
Zp((o0)
+
Zp((o0) + Zr((oo) ls((o~
L((oh)
Zr((oh)
4- Z ( ( o h )
4- Z p ( ( o h )
9
+
g
M i
n:ll
2. The harmonic suppression performance
An equivalent circuit ( F i g . 2 ) was used to
investigate the transfer function H I (j(o) 9
Equations ( 3 ) and ( 4 ) for fundamental ( COo)
and Equation ( 5 ) for harmonics ((oh) can be derived as follows:
For fundamental
_
n
Fig.2
The equivalent circuit of proposed SHAPF
we can get
V~
H, (fioo)
=
Zp((oo)
I~- =
nz
(4)
For harmonics
V~((oh) = I s ( ( o h ) " j(oh " Lz + / t ( ( o h )
"
j(ohM
"
(Zr +
(oh
"
L1) +
G - Mwh
It((oh)
(2)
Where Zr is the output current and voltage of
the Current Controlling Voltage Source ( C C V S ) ,
that is the VSI, controlled by residual harmonic
current of the source branch ( Is ((oh) with gain
G. Ir is the current supplied by the VSI .
Equation ( 2 ) shows that the fundamental
current component flowing into/out of the VSI is
almost eliminated if Zp ( COo) I ~z I Z , ( COo) 9
!
!
i
V~h = G 9 I s ( ( o h ) " I r
Is(cOb) 9 M(oh
///jwhLsl
/r((oh)
Is
=
/r((oh)
=
Zr((.Oh)
4- (-oh " L 1
Is(oh)
v~
Ht (j(oh) -- l,h
G - Mooh
M 9 (oh
= Zr(COh) + (oh " LI
Using
+ (ohL2,
M ---- ~ / L 1 L 2 and LI = n 2 9 L2
H1(j(oh) -
G _ K
n
(5)
From Equations ( 4 ) and ( 5 ) , we can conclude :
This structure SHAPF has the same transfer
function for harmonics control as that reported in
literature ( P e n g et a l . , 1988; Bhattacharya et
a l . , 1 9 9 5 ) . It acts as a harmonic isolator with
equivalent resistance K .
SHAPF with extremely low resistance to fun-
396
CHEN Guozhu, LU Zhengyu et al.
damental current can be produced by proper design.
1988, S. Bhattacharya et a l . , 1995).
lOOo;oo
3. The rating and protection of the VSI
-100.00 L
100.00,
The three phase APF-VSI's rating is determined by
S, = 1 V
r
Ixl
I r Ix3
-100 00 l / ~ ' " ' ~ \
300.00 . . . . . .
(6)
/~
-300.08
1000
Here V~h : G - I~ ( C-Oh ) , and L is given by
Equation ( 2 ) . To achieve the same system suppression performance, residual harmonic current
I~ ( cos ) , under the conditions of Equation ( 1 ) ,
we can find that the first term of Equation ( 2 ) is
Zp (
)
reduced by Zp ( coo ) + Z r( coO ) ' while the sec-
_
r
t
~
-10.08 - - -
48o.0o
48o.08
508.08
Time (ms)
108.00 - - 0.08
-100.00
100.00
..<
ond term is almost constant in the application of
the proposed S H A P F . What is more, the first
0.00,
term of the Equation (2) is usually m u c h larger
4
0.00 ~ , . / '
~
~ - ~
~ F ~ , / ~ - f ' ~ _ f%J
than the second term in a conventional S H A P F
-10.08
460.00
480.00
500.00
( Zp --~ ~ ). That is to say that the rating of the
Time (ms)
VSI without this structure is mainly fundamental,
Fig. 3
SHAPF harmonic suppression simulation F r o m
t o p to bottom: s o u r c e c u r r e n t 1~ , hind c u r r e n t
and it is sharply reduced by the proposed
l L , inverter output voltage Vm~(V~) , inverter
S H A P F . Also, the S~ is reduced dramatically.
current I~(1~) ( a ) Conventional SHAPF; ( b )
With the PPFI providing a fundamental
SHAPF with proposed structure
channel for the main coupled current, this
S H A P F structure can easily protect the VSI from
From Fig. 4, we can see that the VSI fundao v e r - current, and can provide uninterrupted mental current is greatly reduced from 6 . 7 A to
power supply to the load when the VSI faults.
0 . 3 6 A with the proposed structure. The losses,
This was one of the difficulties limiting the
SHAPF actual application formerly ( S . Bhatta7.00
charya, 1 9 9 5 ) .
]
-
-
5.25
SIMULATION RESULT
3.50
1.75
To test the aforementioned rules and principles, a detailed simulation was done over the set
of parameters below.
Load rating 50 kVA/380V 3 ~ ;
Transformer ratio n = 1 0 : 1 ;
PPF1 branch:
0.0t]
O.O0
Q
co" 138'uF) ~ '
(a)
5,25
350
1.75
5o
Some results are shown as follows:
Fig. 3 shows us that the new structure
SHAPF has the same good performance for harmonic suppression as the harmonic suppressor
systems reported in literature ( F . Z. Peng et al. ,
500.00
7.00
J
Zp = 0 . 2 + j ( co . 3 O m H -
250.00
Frequency (Hz)
0 0 0 ~ . J x0.00
A
/%
250.00
Frequency (Hz)
(b)
F i g .4
VSI current speclrmn
(a) conventional SHAPF;
(b) proposed SHAPF
A NEW STRUCTURE OF" SERIAL HYBRID ACTIVE POWER FILTER
which are square functions of the c u r r e n t , s h a r p ly drop down. A l t h o u g h the harmonic current of
the VSI is increased a little, it is not very serious. Especially in higher power system this small
increase can be i g n o r e d .
If this structure S H A P F is applied to higher
power rating s y s t e m , for a 10 MVA s y s t e m , for
example, the rating of the VSI can be r e d u c e d
from the typical 5 0 0 k V A to 20 - 30 k V A . W h i c h
is valuable in practical applications.
CONCLUSIONS
The new structure serial S H A P F a n d its designing rules are p r e s e n t e d in this p a p e r . A n a l y sis and simulation results showed that this
S H A P F has good p e r f o r m a n c e for h a r m o n i c suppression. It is simpe but c a n reduce the A P F inv e r t e r ' s power rating and r e d u c e e n e r g y losses
and cost significantly. The new S H A P F c a n give
highly reliable protection against harmonic currents. It is suitable for high power a p p l i c a t i o n .
397
References
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