First International Power and Energy Coference PECon 2006
November 28-29, 2006, Putrajaya, Malaysia
422
Modeling Of Three-Phase Harmonic Rectification
Scheme Using Three-Phase Inverter
As A Current Injection Device
Mohd Najib Mohd Hussain, Nasrudin A. Rahim
Abstract - In this paper, new harmonic reductions of
the three-phase rectification concept with harmonic
current injection technique are presented using threephase inverter as a current injection device. The
injection current based on zero-sequence triplen-odd
harmonic will automatically generate and then
circulated through the ac side of the three-phase
rectifier via the Zig-Zag transformer which provides
low-leakage impedance for the current harmonics
generated, resulting in pure sinusoidal input current
in the three-phase diode bridge rectifier. The
modeling and simulation of the new proposed current
injection device are verified and compared with a 1.5kVA prototype provided [1].
I. INTRODUCTION
Traditionally, three-phase AC to DC conversions is
performed by three-phase diode rectification
scheme. Obviously these rectifiers draw nonsinusoidal currents or reactive power from the
source, thus the power quality of the distribution
network is greatly deteriorated, resulting in low
efficiency of utilities due to high total harmonic
distortion (THD) of the input three-phase rectifier.
Recently, many approaches have been proposed to
eliminate the existence of harmonic currents in the
input of the three-phase rectification scheme.
Harmonic current injection technique have gained
great attention as a good solution to reduce the
harmonics, since they make the input of the threephase rectifier draw a pure sinusoidal currents form
the power distribution network. This method has
advantages of relatively low cost and high
efficiency and can be applied to medium as well as
to high power rectification over 1 MVA. The main
part of harmonic injection method is the current
injection device [1].
Among the current injection devices that have been
used in [1]-[3], the three-phase inverter is the best
alternative to provide injection current to the input
of the three-phase rectifier in order to obtain low
total harmonic distortion as well as high efficiency.
Basically, three-phase inverter incorporates with
1-4244-0273-5/06/$20.00 C2006 IEEE
three-phase transformer (two windings) and
inductor to actively produce zero-sequence triplenodd harmonics. This current harmonic will
circulate in the ac side of the three-phase diode
bridge rectifier through the Zig-Zag transformer [5]
to produce a current that will be subtracted from
the remaining three-phase rectifier input current
and thus resulting in a pure sinusoidal input current
on the ac side of the scheme. The complete circuit
of the new proposed scheme is illustrated in figure
1.
In this paper, the devices that were used in the new
proposed scheme and the optimization of current
injection are also analyzed in order to achieve
minimum total harmonic distortion (THD). The
results of the analysis obtained were compared with
previous approach to determine the advantages of
the new proposed scheme approach.
It is shown that the THD of the new propose
scheme is equal to 0.05% under unbalanced source
condition while for balanced source condition the
THD approximate to 0.09% compared to the THD
for a previous approach [1] when using two halfbridge as current injection device which THD equal
to 0.45%. According to the recommended
guidelines and standards such as IEEE 519 [4], the
THD obtained form the proposed scheme are
acceptable limits.
423
Figure 1: A three-phase harmonic rectification scheme using three-phase inverter as current injection device
II. CURRENT INJECTION APPROACH
In order to eliminate the harmonic current in the ac
input waveform due to non-linear load application,
this method have been approved to prevent the
current harmonic from damaging the equipment or
malfunction operation of the system.
The harmonic reduction concept in this thesis is
established based on the current injection system
which consists of a current injection network and
current injection device. The current injection
network is a three-terminal network applied to form
the injected current from the basis of the diode
rectifier output terminal voltage and . The current
injection device is applied to divide the injected
current in the three equal current denotes as, and
hence to inject them back to the rectifier supply
lines as shown in figure 2.
Figure 2: Harmonic reduction of three-phase
rectifier with current injection
The current injection devices which are to be
designed should satisfy the following requirements
i.
There should be no increased dc-link
voltage, because higher dc-link voltage
warrants redesign of the pulse width
modulation (PWM) inverter [6].
ii.
No additional components in series with
the power flow path should be used, due
to increased losses [6].
iii.
Using the diode and the IGBT of the
inverter circuit, lower cost can be
achieved for high power applications
purpose.
While the requirements for the harmonic reduction
of three-phase rectification should be
i.
The harmonic distortion of the input
current should be as low as possible and
the resulting input current should be
sinusoidal.
ii.
The operation of the rectifier should be
independent of the line impedance
because when a non-linear load draws
current that current passes through all of
the impedance that is between the load
and the system source. As a result of the
current flow, harmonic voltages are
produced by impedance in the system for
each harmonic.
iii.
No additional or switching devices in
series with the main power flow path [6].
iv.
The circulating harmonic current should
be automatically generated by the
proposed novel interconnection.
v.
The cost, power losses and size compared
to the diode rectifier should be as small as
possible.
III.ANALYSIS OF THE PROPOSED SCHEME
The analysis of the current injection system can be
depicted of a current injection network and a
current injection device. The current injection
network is a three-terminal network applied to form
the injected current on the basis of the diode bridge
output terminal voltages [7]. The zero-sequence
sources from the current injection devices going to
the input terminal of three-phase diode rectifier as
an injection current through the Zig-Zag
transformer [8]. The performance of the Zig-Zag
1~ .
transformer to provide the injection current will be
determined by the performance of the input current
sources of the scheme.
f$Et
The modeling of the proposed scheme is designed
using the following parameters [1]:
*
Input: 220 V/50 Hz, 15kVA;
*
Switching frequency: 2 kHz;
*
Load power,: 10 kW;
*
Output Inductor: 4 mH
..
424
..
..
..
.,.
i~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Figure below show the power circuit of the threephase rectification scheme.
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ae
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F-
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m
M
MCARI
x
1Vclt.g=- R.-gLd.tc-
.`=-f
. . . . ... . .
,...........
~~~~~~~~~~~~~~~~~~
Figure 3: Control and reference signal block
I
I
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LOI
I
I
...
I
I
I
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...
.
...
0
..
0.01
0.03
0.02
0.04
0.05
0.06
0.07
0.08
Figure 5: The resultant of AC side waveform for
a new proposed scheme
Figure 4: Voltage Regulator block
',,of)f 5i cycles. Lf selecte d signa
101
IV. EXPERIMENTAL RESULTS
A.
Unbalanced source condition for
proposed scheme
new
_0-015
In the simulation of three-phase rectification
scheme, the unbalanced source voltages can cause
by unequal load distribution in each phase. Since
the unbalanced three-phase voltages contain a zerosequence voltage, and this will generate a
significant fundamental component flow between
the source, the neutral conductor on the source side
and the Zig-Zag transformer [9]. Figure 5 show the
input side waveforms of the three-phase rectifier
and figure 6 illustrate the FFT analysis of the
waveforms.
0-02
0
02f 50 0-0 0-35 0-04
0-045
Tire i.s)
J--i
0-005
0. 0' -3
0.131O
0.0
o
0
5f
10
1D
L
25
Harmonic Order
30
3 5f
Figure 6: FFT Analysis for Unbalanced source
0.09
0.1
.
.
.
.
.
.
.
425
more effective to reduce the input current
harmonics of the three-phase rectifier in terms of
distortion factor in order to meet the total
harmonics distortion (THD) requirement and
standards obviously to be less than 5% compared
with previous approach in [1]. The design of the
control and reference signal for this new approach
is simpler compared with previous approach. This
is because these new scheme only need one PWM
generation pulse for IGBT compare with using two
PWM generation pulse for separate IGBT of the
single-phase inverter in the previous scheme.
Therefore, this new proposed scheme will result in
relatively low cost as well as provide high
efficiency which can be applied to medium and
high power rectifications.
Balanced source condition for new
proposed scheme
B.
The results for this condition are shown in figure 7
and figure 8 respectively as below.
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ae
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ACKNOWLEDGEMENT
The authors wish to express their thanks to
Associate Prof. Dr. Ahmad Maliki Omar, for all the
support and guidance during implementing this
research.
REFERENCES
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Figure 7: Input waveform under balanced source
voltages
1 of selected sipal
2 Ltf cycles
,n-
I
-10,
.131
0-01-5 0.02 0.025 0-03 0. 03 - 5 0.04 0 045,
uidauental
z50Hz
=
489
-D
=
0091
Ha
Figure 8: FFT Analysis for balanced source
V. CONCLUSION
The current injection harmonics using three-phase
inverter approach has been analyzed and
implemented in this paper. The simulation results
obtained proved that this new proposed scheme is
U1
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