IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008

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A Novel Three-Phase PFC Rectifier Usinga Harmonic Current Injection Method
Jun-Ichi Itoh, Member, IEEE, and Itsuki Ashida

Abstract—This paper proposes a novel circuit topology fora three-phase power factor correction (PFC) rectifier using aharmonics current injection method. In consideration of lower
cost, the harmonics injection method is more suitable than aconventional six-arm pulse width modulation (PWM) rectifier.
The harmonics injection current is simply generated by only one
switching leg. As a result, the proposed circuit has the advantage
of only two switches. An optimal injection current is achieved inorder to obtain an input current of sinusoidal waveforms. This
paper discusses the basic operation and optimal design method
for the proposed circuit. In addition, the validity of the proposed
circuit is confirmed by simulation and experimental results. An
input current of almost sinusoidal waveform was obtained andan input current total harmonic distortion (THD) of 8.5% was
obtained at a load of approximately 1 kW.
Index Terms—AC–DC power conversion, converters, harmonic
distortion, power conversion harmonics, power quality, rectifiers.

I. INTRODUCTIONECENTLY, the harmonics current in a power grid cancause various problems, such as line voltage distortion,
heating of power factor correction capacitors and so on. Powerfactor correction (PFC) rectifiers, which suppress the harmonics
current, are still a very important technology. One of the mostpopular PFC methods for three-phase input is a full-bridge
type pulse with modulation (PWM) rectifier, which consistsof six arms and a boost-up reactor. The conventional PWM
rectifier can obtain a sinusoidal input current without harmonics
distortion. However, in regard to cost, the conventional PWM
rectifier is not the best solution for the PFC. On the other
hand, many three-phase PFC rectifiers that use current injection
methods have been proposed [1]–[10]. These types of rectifiers
can realize a low cost system, because they do not require many
switching devices in comparison with a conventional PWM
rectifier. One famous rectifier that uses the current injection
method is called the Minnesota rectifier [1]. This circuit uses
two boost-up choppers in part of the dc-stage. The Minnesota
rectifier contains many switching devices in the main current
path. Therefore, it is difficult to obtain high efficiency due tothe increase in conduction losses from the switching devices in
the main path.
This paper proposes a new simple three-phase PFC rectifier
using a harmonic current injection method. The proposed circuit

R

Manuscript received May 29, 2007; revised August 30, 2007. Recommended
for publication by Associate Editor H. D. Mouton.
The authors are with the Department of Electrical, Electronics and Information Engineering, Nagaoka University of Technology, Niigata 940-2188, Japan.
Digital Object Identifier 10.1109/TPEL.2007.915774

consists of two switching devices; two LC filters and a harmonic
injection network. Thus, the proposed rectifier can realize lower
cost than the conventional injection type PFC rectifiers. In addition, high efficiency is achieved, because the main current passes
through only two diodes in addition to the diode rectifier. The
injection current is controlled by the optimum method given in[4], in order to suppress the input current distortion. This paper
describes the features of the proposed rectifier, and gives detailsof the operation and the optimum design method. Simulationand experimental results show the validity of the proposed circuit and design method.
II. CIRCUIT TOPOLOGY
A. Harmonic Current Injection Method
Fig. 1 shows the basic circuit configuration of the current injection method. The principle of this method is that the input
current is composed of an input current of the diode rectifier
and an injection current as shown in Fig. 1(b). When the injection current , is defined by (1), the harmonic component in the
input current can be expressed by (2)(1)(2)
is the dc link current, is the angular frequency ofwhere
the input voltage, and is the injection current gain. Here,is calculated as the difference between
and . in Fig. 1(a).
Therefore, the amplitude of depends on .
Although the 1/5 and 1/7 of the fifth and seventh harmoniccomponents are contained in the diode rectifier current , thosecomponents are decreased by the injection current gain, . The
optimum injection gain is set to 3/4 in order to obtain minimum values of the fifth and seventh harmonics components.
Fig. 2 shows examples of the harmonic current injection network. The harmonics current is equally injected through thesecircuits to ac side. The power capacity of the injection network
is not so large, since each phase current becomes about 1/4 ofthe dc link current. It should be noted that if a system has an
isolation transformer in the input side, the neutral point of the0885-8993/$25.00 © 2008 IEEE
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Fig. 3. Main circuit of a Minnesota rectifier.

Fig. 1. Circuit for the harmonic current injection method. (a) Circuit configuration. (b) Current waveform.

Fig. 4. Main circuit of the proposed three-phase harmonic current injection
method PFC rectifier.

neutral point voltage of the power supply(4)
Fig. 2. Harmonic current injection network. (a) Tuned LC filter. (b) Star/deltatransformer. (c) Zigzag transformer.

where

represents the peak value of the input voltage.

C. Proposed Circuit
isolation transformer can be used instead of the injection network.
B. Conventional Circuit
Fig. 3 shows one of the conventional three-phase PFC rectifiers using the harmonic current injection method, which iscalled a Minnesota rectifier. This rectifier consists of a threephase diode bridge rectifier, two series-connection boost converters, and the harmonic current injection network. In this cirandcuit, the injection current is generated by controlling. The injection current is obtained using

Fig. 4 shows the main circuit of the proposed three-phase PFC
rectifier, which uses a single leg for the harmonic current injection circuit. This rectifier requires a three-phase diode bridge, aswitching leg that consists of and , a filter reactor , filter
capacitor , a dc reactor , and the harmonic current injection
network. The harmonic component of the switching frequency
in the dc current is reduced by the LC-filter.
In this circuit, the injection current is directly controlled byand . The injection current flows depending on the voltage
difference between points P or N and point M. That is, whenis turned on, the injection current can be obtained by (5), if theis neglectedcurrent of the capacitor(5)(3)
The features of this circuit are as follows: the efficiency decreases because the main current path contains two diodes in
is conaddition to the diode bridge part; the output voltage
strained in (4), because the boost converter is used based on the

Similarly, whenthat given by

is turned on, the injection current becomes

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(6)

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717

Fig. 6. Control block diagram for the proposed circuit.

Fig. 5. Input current reference and i 3.

whereis the leakage inductance of the current injection
network.
Hence, it is possible to control the injection current, since
the increase and decrease of the current can be controlled byand , as shown in (5) and (6). It is noted that the output
voltage of the proposed circuit becomes the same as a normal
three-phase diode bridge.
The proposed rectifier has following advantages over the conventional rectifier (Minnesota rectifier).
a) High efficiency is obtained because the main current
passes through only two diodes, which are used as adiode bridge.
b) The filter reactor realizes a reduction in size, due to the folrelowing ac current. In the conventional circuit,quires a dc reactor. The volume of the ac reactor is smaller
than the dc reactor.
III. CONTROL STRATEGY
Fig. 5 shows the relation between the input current commandand the optimum injection current command . As discussed
in chapter II, the injection current can improve the input current
waveform to a sinusoidal current. In this chapter, we apply an
optimum harmonic current to the proposed circuit. While theis blocked by the diode rectifier, the injection current only appears in the input current. Hence, the waveform of has to fit toa part of the sinusoidal waveform if we want to achieve a sinusoidal input current. As a result, the optimum harmonic current
is obtained by the middle signal in the three-phase current command, as show in [4]. Therefore, the optimum harmonic current
command is obtained by(7)
where represents the maximum input current command, andrepresent the minimum input current commands. When the dc
link current is constant and the impedances of the power supply
are the same in each phase, the injection harmonics current comin Fig. 4 are the same. Therefore, the proponents of andposed circuit can achieve a sinusoidal input current with only

one current control. The input current commands are unity sinusoidal waveforms, which are synchronized with the power
supply voltage.
Fig. 6 shows the control block diagram of the proposed circuit. A hysteresis current controller is applied in order to suppress the switching ripple of the injection current. In this case,the ripple current can be controlled by the bandwidth of the, andhysteresis current controller. The input voltages
are detected in order to calculate thedc inductance current. It should be noted that
input current commands
an inexpensive detection circuit, such as a shunt resistor, can beused since the dc link current detection does not require quick
response or high accuracy. The optimum harmonic current comis calculated from, and (7).
mand
IV. CIRCUIT DESIGN
A. Design of the dc Link Reactor
In the proposed circuit,and , shown in Fig. 4, dependand ,on the difference between the dc link reactor current
although is directly controlled by the hysteresis current regulator. Therefore, to suppress the distortion of the input current,
must be maintained as constant.
the dc link reactor current
is caused by the diode bridge output
However, the ripple ofvoltage. When the switching leg in the proposed circuit
is obtained as follows:
stops switching,(8)Note that the sixth harmonic current in (8) is the dominantcomponent in the ripple component of. When the switching
includes the spike voltage, as discussed in [12].
leg works,
is still the dominant comHowever, the sixth harmonic in
ponent because the influence of the spike voltage is not large.
Therefore, only the sixth harmonic current is considered in thefollowing discussions. The ripple rate of the dc current causedby the sixth harmonic current is equal to the ripple rate of theoutput power under constant dc voltage. That is, the total harcan be calcumonics distortion (THD) of the dc side
lated by
(9)is the peak value of the sixth harmonic current,
where,
is the fundamental frequency component of the input current,

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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008

Fig. 9. Relation between the dc link reactor and the input current THD.
Fig. 7. Simulation circuit for the ripple analysis.

Fig. 9 shows relation between the value of the dc link reactor
and the THD of the input current, and is derived from (9) and(12). The value of the dc reactor is expressed by the percentage
unit based on the power supply voltage, frequency and converter
power capacity. It is suggested from Fig. 9, that the dc reactorof 10% is required in order to obtain an input current THD of
less than 10%.
B. Design of the LC-Filter
Fig. 8. Distortion in the input current depending on the ripple rate of i.

, and are the fifth, sixth and seventh harmonic components for the input current, is the value of the dc current, andis the input voltage.
The fifth and seventh harmonic components in the input current appear when the dc current contains the sixth harmonicis calcucomponent. Then, the input current THD
lated by (10).
(10)
Therefore (11), which expresses the relationship between
andis derived from (9) and (10).
(11)
Fig. 7 shows the simulation circuit used to confirm the proprietyof (11). Ideal current sources are used instead of the switchingleg and the dc reactor. The current source
assumes the
ripple of the sixth harmonic in the dc current. The relationshipandis investigated by changing the magof
nitude of the current source.
Fig. 8 shows the comparison of the simulation results andcalculated results from (11). The simulated results agree wellwith the calculated results using (11). In this case, the relationis almost theof (12) is obtained, because the magnitude ofsame as the magnitude of(12)

The propriety of (12) was identified as simulation result byagreement of (12).

The proposed circuit reduces the harmonic component of theswitching frequency using a LC-filter. The filter reactor
andare connected in parallel with the output side ofcapacitor
the diode bridge. There are two factors that influence the input
current in the LC-filter design.
1) Phase Shift of Harmonic Current: Fig. 10 illustrates theinfluence of the LC-filter using a simulation waveform of the
input current when the phase between the injection current
and the dc currentoris delayed by the LC-filter. The
phase shift from the LC-filter causes the distortion of the input
current, because the current can not pass through the dioderectifier, except for only 60 degrees in the half period of thepower supply. Fig. 10(b) shows the relationship between the
input current THD and the phase shift by the simulation. As
a result, the input current THD increases in proportion to thephase shift.
The input current THD can be reduced by increasing theimpedance of the LC-filter, because the phase shift is causedisby the LC-filter current. The impedance of the LC-filter
expressed by(13)
Fig. 11 shows the relation between the impedance ratio ofto the rated impedance , which is based on the rated voltage,
frequency and power capacity, and the input current THD. It isnoted that the decrease of the input current THD depends on theincrease in .
2) Harmonic Component of the Switching Frequency: If theof the LC-filter is close to the switching
cutoff frequency, the harmonic component of theremains.
frequency
Therefore, thehas to be designed at a sufficiently low frecauses a phase shift,quency for the . However, too low a
as discussed previously.
depends on
On the other hand, the switching frequency
the hysteresis width, the impedance of the current injection

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ITOH AND ASHIDA: NOVEL THREE-PHASE PFC RECTIFIER

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Fig. 12. Relation between the filter and the input current THD.

region from 20% to 90%,
power supply for (13). In thethe increase in the input current THD depends on the increaseof the cutoff frequency, because the harmonic component of theswitching frequency dominates the distortion of the input curregion around 10%, the input current
rent. However, in the
THD is increased from the influence of the phase shift. Simiregion under 50, the LC-filter current
larly, in case of thecauses distortion of the input current.
Fig. 10. Influence of the phase shift of the harmonic current on the input current THD. (a) Simulation waveform for input current. (b) Input current THD
dependence on the phase shift.

Fig. 11. Relation between Z =Z and the input current THD.

network, and the filter reactor , as shown in (14), because
the PWM pattern is used by the hysteresis current regulator

C. Example of the Circuit Design
The circuit parameters can be designed from Figs. 9 and 12 inorder to realize the desired input current THD. For example, an
input current THD of less than 10% can be designed for the proposed circuit. Firstly, the cutoff frequency is selected as 20% of
the switching frequency, using Fig. 12. Then the impedance ofis simultaneLf is obtained at 2.4%, and the admittance ofously determined as 5.5%. As a result, the design point in Fig. 12
is selected at an input current THD of approximately 8%. The
sixth harmonic current is dominant in the THD that is caused by, and the resonant frequency ofthe dc link reactor
the LC-filter dominates the harmonics components of the input
current THD. Therefore, the allowance for the dc reactor current
is obtained by (15), using. which dominates
the resonant frequency. In this example, the dc reactor current
THD has to suppress less than 6%. Lastly, the value of the dc
reactor is determined as 14% from Fig. 9

(14)
where
means the maximum input voltage.
andare designed from (14).
Fig. 12 shows the relationships among the input current THD
and the LC-filter parameter when the dc reactor current is maintained constant. The input current THD in Fig. 12 is obtainedby the simulation using the parameter variation of the LC-filter, which is obtained by substituting the resonant
impedance
frequency of the LC-filter for (13). The horizontal axis of Fig. 12
denotes the ratio of for switching frequency , and the vertical axis denotes the ratio offor the rated impedance ,which is obtained by substituting the rated frequency of the%(15)
V. SIMULATION AND EXPERIMENTAL RESULTS
Table I shows the experimental and simulation conditions
that were derived in chapter III-C. The simulation is used inorder to check the fundamental operation and the validity of
the circuit parameters. The switching frequency depends on thehysteresis bandwidth and the reactor as already explained. The
switching frequency is designed to be approximately 10 kHz.
The variation of the switching frequency according to the ripple
is less than 1 kHz in this condition. Note thatof

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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008

TABLE ISIMULATION CONDITIONS

Fig. 14. Experimental results for the proposed circuit.

Fig. 13. Simulation results for the proposed circuit.

the dc reactor appears to have a large value. However, the dc reactor for use with an electric inductor [11], [13] or a current typeload can be small. The terminal voltage of the transformer becomes the half the input voltage, and the current of transformer
decreases to 1/3 the input current. Therefore, the rated power of
the transformer can be suppressed to approximately 20% of theoutput power if the converter loss is neglected.
Fig. 13 shows the simulation results of the proposed circuit
using the parameters of Table I. A THD of 7.2% and a unity
power factor are obtained. In addition, a constant output voltage
on the dc side is also obtained. It is noted that the one of thecauses of this is the dc link current ripple, which occurs withthe current distortion around the peak of the input current.
Fig. 14 shows the experimental results of the proposed circuit with a resistive load under the same condition as shownin Fig. 13. We can confirm that the sinusoidal input current andunity power factor are obtained are the same as the simulated results. Furthermore, it is confirmed that the output voltage is also
maintained constant. A THD of 8.5%, which is almost the sameas the simulated results, was obtained. We believe the causes forthe difference between the simulated and experimental results tobe the accuracy of the circuit parameters and the imbalance in
the impedance of the power supply.
The ringing is caused by the dc current ripple and filter current ripple. The minimal or maximal part of the input current
consists of the injection current and the dc current. Therefore, if
the dc current contains ripple components, the input current distortion appears. Note that the current distortion does not appear
in the middle part of the input current because the middle partconsists of only the injection current, which is controlled by theswitching leg. In order to suppress the input current distortion
more than this, the switching frequency or the dc reactor should
be increased.

Fig. 15. Spectrum analysis result of the input current and the IEC-61000-3-2
standard.

Fig. 15 shows the spectrum analysis results of the input
current and the IEC-61000-3-2 standard. The proposed circuit
complies with this standard. In addition, the proposed circuit
complies with the IEC-61000-3-4 standard in the low-orderharmonics component even if the rated output power becomeslarge.
Fig. 16 shows the THD characteristics of the input current
against the output power. The input current THD of the proposed circuit increases according to the decrease in the output
power, since the harmonics current is constant, although thefundamental current becomes small in the light load region. In
the present study, we did not consider the impedance of thepower supply. However, the input current distortion is reducedby the impedance of the power supply. On the other hand, theimpedance instability in the power supply causes current distortion because the input current of each phase is not controlled
in the proposed circuit. However, the instability of the power
supply is not a significant problem for a practical power supply,
as shown by the experimental results.
Fig. 17 shows the efficiency and input power factor forthe proposed converter. A maximum efficiency of 96.2% is
obtained. In addition, an input power factor of over 99% is
obtained for a load over 50%. In the light load region, thepower factor decreases, because the THD of the input current
increases as shown in Fig. 16.

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ITOH AND ASHIDA: NOVEL THREE-PHASE PFC RECTIFIER

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by 0.8% compared to the conventional circuit. The converter
loss can be reduced by approximately 20% at the rated loadusing the proposed circuit. It is noted that the difference in theloss between the proposed and conventional circuit increases
according to a heavy load. The reason for this is that thecondition loss of the boost up diode in the conventional circuit
dominates the total loss.

VI. CONCLUSION

Fig. 16. Characteristics of the input current THD.

Fig. 17. Efficiency and input power factor for the proposed circuit.

Fig. 18. Comparison of the converter loss.

TABLE II
EXPERIMENTAL CONDITIONS FOR CONVENTIONAL CIRCUIT

Fig. 18 shows a comparison of the converter loss between
the proposed circuit and a conventional circuit based on theexperimental results. The conventional circuit was made under
the conditions given in Table II. A maximum efficiency of
95.4% was obtained for the conventional circuit at the rated
load. Therefore, the proposed circuit improves the efficiency

This paper proposed a novel three-phase current injection
method PFC rectifier. In addition, the basic operation and optimum design were discussed. The proposed circuit has the following features:— the additional circuit components to the normal diode rectifier are one leg, a LC-filter and injection circuit;— the input current THD is 8.5% at the rated load (1 kW);— the proposed circuit can reduce the converter loss by 20%
that for the conventional Minnesota rectifier.
The validity of the proposed circuit and the optimum design
method are confirmed with simulated and experimental results.
In future study, the volume of the dc reactor will be reduced by
optimum control, depending on the dc current ripple.

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[2] R. Naik, M. Rastogi, and N. Mohan, “Third-harmonic modulated
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[6] A. R. Prased, P. H. Ziogas, and S. Manias, “An active power factor correction technique for three-phase diode rectifiers,” IEEE Trans. PowerElectron., vol. 6, no. 1, pp. 83–92, Jan. 1991.
[7] S. Kim, P. N. Enjeti, and P. Packebush, “A new approach to improve
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Nov./Dec. 1995.
[8] S. Kim, P. N. Enjeti, D. Rendusara, and L. J. Pitel, “A new method toimprove THD and reduce harmonics geberated by a three phase dioderectifier type utility interface,” in Proc. IEEE IAS Annu. Meeting, 1995,
pp. 1071–1077.
[9] J. C. Salmon, “3-phase pwm boost rectifier circuit topologies using
2-level and 3level asymmetrical half-bridges,” in Proc. IEEE APEC’95,
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[10] B. M. Bird, J. F. Marsh, and P. R. McLellan, “Harmonic reduction in
multiplex converters by triple-frequency current injection,” Proc. Inst.
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[11] H. Funato and A. Kawamura, “Analysis of variable active-passive reactance,” in Proc. PCC’93 Conf., Yokohama, Japan, 1993, pp. 842–848.
[12] P. Boz̆ović and P. Pejović, “Current injection based low harmonic
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722

Jun-Ichi Itoh (M’01) was born in Tokyo, Japan, in
1972. He received the M.S. and Ph.D. degrees in electrical and electronic systems engineering from Nagaoka University of Technology, Niigata, Japan, in
1996, 2000, respectively.
Form 1996 to 2004, he was with Fuji Electric
Corporate Research and Development, Ltd., Tokyo,
Japan. Since 2004, he has been with Nagaoka
University of Technology, Niigata, Japan as Associate Professor. His research interests are matrix
converters, dc/dc converters, power factor correction
techniques and motor drives.
Dr. Itoh received the IEEJ Academic Promotion Award (IEEJ Technical Development Award) in 2007. He is member of the Institute of Electrical Engineersof Japan.

IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008

Itsuki Ashida was born in Niigata, Japan, in 1983.
He received the B.S. and M.S. degrees in electrical,
electronics and information engineering from Nagaoka University of Technology, Nagaoka, Japan, in2006 and 2008, respectively.
Since 2008, he has been an employee of Fuji Electric FA Components and Systems Co., Ltd. His main
research interests include power factor correction(PFC) rectifiers, new converter topologies.
Dr. Ashida is a member of the Institute of Electrical Engineers of Japan.

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