Comparison of Boost Chopper and Active Buffer
as Single to Three Phase Converter
Yoshiya Ohnuma

Jun-ichi ItohStudent Member, IEEE
Nagaoka University of Technology
1603-1 Kamitomioka-machi Nagaoka City
Niigata, Japanohnuma@stn.nagaokaut.ac.jp

Member, IEEE
Nagaoka University of Technology
1603-1 Kamitomioka-machi Nagaoka City
Niigata, Japan
itoh@vos.nagaokaut.ac.jp[5]. These circuits add the a few switching devises andenergy buffer such as capacitor or reactor to the conventional
boost chopper. Certainly, the voltage ripple in the DC partcan be reduced by the control of the energy buffer even if thesmall something capacitor is used in DC part. However, theadditional circuit for the power decupling causes increasing
the power loss.

Abstract—This paper presents a comparison in terms ofefficiency and volume between the single-to-three-phase power
factor correction (PFC) converter. A conventional PFC circuitthat consists of a boost chopper requires a large boost-up
inductor and large smoothing capacitors to decouple the power
ripple. The size and efficiency of the converter become adiscussion issue recently. On the other hand, a single-to-threephase power converter using an active buffer has been
proposed. The active buffer does not require a large inductor
and large smoothing capacitors in the DC link part. These two
types of converters are designed and simulated to calculate thelosses. In addition, a prototype converter has been built andtested. The efficiency achieves 94.6% at 1.5-kW same as thecalculated efficiency. Furthermore, the efficiency increases by
1.5% comparing to the conventional converter. In addition, thevolume is decreased by approximately 0.7 times then the size ofthe conventional converter.

I.

Apparently, a single-to-three-phase power converter withan active buffer (proposed converter) as shown in Fig. 2 hasbeen proposed in [6] in terms of loss reduction of the power
decoupling circuit. This converter is based on the concept of
an indirect matrix converter that coupled with an active
buffer to decouple the power ripple. The converter obtains
sinusoidal waveforms on the input and output current. In
addition, the size of the converter is reduced because theconverter does not require a large smoothing capacitor and alarge boost inductor in the DC link part. However, theclarifying of the efficiency and the volume are remained
unidentified.

INTRODUCTION

Single-phase to three-phase converters achieve energy
saving in the application of home motor appliances. One of
the important requirements of the converter is to provide low
input current harmonics. Therefore many power factor
correction (PFC) converters and control methods have been
proposed [1]-[3]. At the same time, studies on the highefficiency and design of the volume are very important
subjects in this field. The most common structure of PFC
converter is the single-switch boost chopper circuit(conventional converter) as shown in Fig. 1 [1]. This circuit
can control the input current easily. However, this converter
requires a large boost-up inductor and a large smoothing
capacitor to decouple the power ripple, which is a frequency
twice of the power supply at the DC link part. In addition,
the DC link voltage is always higher than the maximum
input voltage because a boost-up converter is used. Therefore
the switching loss of this conventional converter becomeshigh.

This paper demonstrates a comparison on the efficiency
and the volume among these converters. At first, the paper
discusses the circuit layout and control methods for thesesingle-to-three-phase PFC converters. There are two type ofboost up operation modes which are known as thecontinuous current mode (CCM) and the discontinuous
current mode (DCM). Second, each parameter of the passive
components is designed and utilized in the simulation
analysis in order to compare the losses of these converters.

In order to reduce the volume of the smoothing capacitor,some power decoupling converters have been proposed [4],978-1-4577-0541-0/11/$26.00 ©2011 IEEE

Fig.1 Conventional converter.

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Then the size of the heat sink is calculated based on thesimulation results. Nevertheless, a prototype of the proposed
converter has been built and tested in order to validate theloss analysis. As a result, the efficiency of the proposed
converter is 1.5 % higher than the conventional converterwith DCM boost chopper. In addition, the total volume ofthe passive components is approximately decreased by 0.7
times comparing to the conventional converter with CCM
boost chopper.
II.

Active buffer
Dr1

Dr2

L
Dp

•

The current of an inductor is either CCM or DCM.

•

Duty ratio of the switch in boost chopper is either
constant or variable.

•

Frequency of the switch in boost chopper is either
constant or variable.

M

SL

Dr4

Diode
rectifier

CIRCUIT CHARACTERISTICS

Cdc

Charge Discharge
circuitcircuitInverter
circuitFig.2 Proposed converter.

(a) Conventional converter with CCM

The simplest controls such as constant duty ratio, constantfrequency or line frequency commutated control can obtainhigh power factor easily for low power applications.
However, the input current remains distorted at low voltage
boost ratio. On the other hand, advanced control strategies
can control the input current into a clear sinusoidal
waveform based on the duty ratio or switching frequency. In
this paper, CCM or DCM operation with constant switchingfrequency and variable duty ratio methods are discussed.

(b) Conventional converter with DCM(c) Proposed method

Figure 2 shows a single-to-three-phase converter with anactive buffer [6]. The active buffer that consists of adischarge circuit and a charge circuit replaces the boost
chopper to decouple the power ripple, which the power
ripple has a frequency that is twice of the power supply. The
discharge circuit consists of a small capacitor and a switch.
The charge circuit is similarly to a boost chopper circuit but
using a smaller inductance value because the current is
controlled based on DCM. The voltage ripple in the DC linkpart is absorbed to the small capacitor Cdc by controlling its
terminal voltage. The terminal voltage of Cdc has large
fluctuation according to the energy ripple which comes fromthe input side.

Fig.3 three different control method diagrams for PFC circuits.

current command and switching period of the switch in boost
chopper, respectively.
Therefore, for both the conventional converters, theinductor current command il* is obtained by a PI controller.
In the proposed control method, the power ripple iscompensated by the discharge circuit and the charge circuit.
The control method of the charge circuit is based on the
DCM. Therefore the duty ratio is determined by (1). It
should be note that the charge circuit and the discharge
circuit are operating alternately at per quarter cycle of thepower grid frequency. Thus, half of the input power is
supplied directly to the inverter. Therefore the inductor
current command il* is calculated by

Figure 3 shows three different control method diagramsfor PFC circuits. The switching duty ratio dl of CCM isobtained by PI controller using the inductor current as shown
figure 3 (a). In contrast, DCM can obtain the duty dl using
the equation without a current sensor as follows:**

il = I IN sin(ωt ) −*2 Lb (vc − vin )il,
vin vc Tsw

SC

Input filter
Lin
Cin

Figure 1 shows a single-to-three-phase converter with asingle switch boost converter. The converter consists of adiode rectifier, inverter and boost chopper. There are many
control methods can be applied into this PFC [1]-[3]. The
point of the control method is as following.

dl =

Dr3

(1)

I IN
,
2 sin(ωt )(2)where IIN* is the amplitude of the input current command andω is the input single phase angular frequency In addition, thecapacitor voltage is fluctuating in this system. Hence, thepower ripple WC which is the electric storage energy is
calculated by the maximum capacitor voltage VCmax andwhere, Lb, vc, vin, il*and Tsw are inductance of the boost-up
inductor, DC link capacitor voltage, input voltage, inductor516

minimum capacitor voltage VCmin. Therefore IIN* can be
expressed by*

I IN =()

2ωWC ωC dc
2
2=
VC max − VC min ,
VIN
V IN

Table 1 Common specification of converters.

(3)

where VIN is the peak value of the input voltage, Cdc is
capacitance of the DC link capacitor. Notice that the
proposed circuit is not implemented with the PI controller, asa result, the transient response for the control of DC link
voltage is fast and stable.
III.

DESIGN OF PARAMETERS

This section explains a design example for a 1.5- kWclass PFC converter. Table 1 provides the common
specification of the converters.
A. Input filter
The input filter for PFC circuit must have enough ripple
attenuation at per switching frequency to satisfy the EMI
requirement. In order to satisfy the above requirements, thecut-off frequency is required to be lesser than 1/5 to 1/10
times of the switching frequency. In this case, we design the
cut-off frequency fcf sets to 1.5 kHz. Also, in order to control
the input power factor closed to unity at the line frequency,
the reactance of input filter Lin is set to 1 % of rated
impedance of converter. From these specifications, we obtain
200
0.01% LZ cov
7.5 = 0.85 mH ,Lin ==2πf in2 ⋅ π ⋅ 50
C in =(

1

Lin 2πf cf

=
2

)

1

(

0.85 ⋅ 10 −3 2π 10 ⋅ 10 3

IL

)

(5)

VIN
V − VIN
Δt on − C
(Tsw − Δton )Lb
Lb

Δt on =

VC − VIN
Tsw
VC

1/(2fin)Lb =V IN (VC − V IN ),2VC I L Δ I L f sw

(8)

where fsw is the switching frequency of the chopper.
Here, the current ripple ratio rl of the inductor, which isnormalized by the peak value IL of average inductor current
for one switching period is expressed in Eq.(9).

.

rl =

ΔI L / 2.
IL(9)Therefore Eq. (8) can be rewritten as
Lb =V IN (VC − V IN ).
2VC I L rl f sw

(10)

The required inductance of the boost-up inductor Lb isdominant at the maximum inductance current IL and the ratioof the inductor current ripple rl. Note that in the inductor
current, the ratio of the inductor current ripple rl is from 0 to
1 means that the inductor current is a continuous current(CCM). Over than 1 means the inductor current is controlled
as a discontinuous current (DCM). Then the peak values ofthe each current mode are calculated by(6)

where Δton is turn on time of the switch in the boost chopper
and VL is inductor voltage of the boost-up inductor. VL equals
vin when the switch is turned on. In contrast, when the switch
is turned off, VL equals to vc minus vin. Therefore, we obtain
Eq. (7) at the maximum ripple of the inductor current.
0=

VCmin

From Eq. (6) and (7), the required inductance of theboost-up inductor Lb is obtained byFirst of all, the ripple of the inductor current is discussed.
The inductor current ripple ΔIL is obtained fromVL
Δt on ,Lb

VC

Fig.4 Definition of inductor current andcapacitor voltage parameters.

B. Boost-up inductor Lb
This section discusses the design of the boost-up inductor.
In order to simplify the derivation, we design the inductor
value based on the peak value of the input voltage. At the
input phase of π/2, the peak value input voltage is VIN and thecapacitor voltage is assumed as the average value VC.

ΔI L =

VC

IL

ton
Tsw

(4)
= 13.2 μF
2VCmax

IL_peak

I L _ peak = I Lrl + I L
I L _ peak = 2 I L rl

(7)

517

, when, whenrl < 1 (CCM)rl ≥ 1 (DCM)

.

(11)

From (11), IL_peak of DCM becomes twice of the IL and more.

Table 2 Design value of parameters

In term of design, we assumed that the ripple ratio of
inductor current rl for CCM is lower than 0.1 p.u. For thecomparisons, rl parameter for the DCM and proposed
converter needs to be 1.1 p.u. From the calculation, theboost-up inductor Lb is obtained as shown in Table 2. Noticethat in the proposed circuit, the value of inductor current IL ishalf of the conventional converters as shown in Eq. (2).
C. DC capacitor Cdc
In the single-phase to three-phase converter, the electric
storage energy required to compensate the power ripple WC
is obtained by
1

4 f in1
WC = VIN I IN ∫ sin (2ωt )dt
0
2,
VIN I IN
=
2ω in

(12)

where IIN is the amplitude of the input current and ωin is the
input single phase angular frequency. Moreover, the WC in
the capacitor is required from the relations between theelectric power and the capacitor voltage by (13).
1122WC = CVC max − CVC min ,(13)22
where, VCmax is the maximum voltage, and VCmin is theminimum voltage of the buffer capacitor.
The electric storage energy used to compensate thepower ripple WC is obtained by (12) and (13). Therefore, theminimum capacitance in the buffer circuit is obtained by(14).
C dc ==

Fig. 5 Experimental results of proposed converter.

2WC
2

VC max − VC min

2

VIN I IN

(14)

ω (VC max 2 − VC min 2 )The capacitance Cdc is obtained from the ratio of thecapacitor voltage ripple rc which is expressed in (15). The
capacitor voltage ripple rc is normalized by the averagevalue Vc of the capacitor voltage for a grid period.
rc =ΔVC / 2.
VC

Fig. 6 comparison efficiency
between experiments and simulations.

the proposed converter, the fluctuation of the DC capacitor
voltage can be controlled by the active buffer. Therefore theratio of capacitor voltage ripple rc parameter is set to 14.3%.
So, requirements for capacitance Cdc of these converts are
obtained as shown in Table 2. However, the selection of theelectrolytic capacitor must consider upon its rated ripple
current. Therefore, we select the closest capacitor that meetthese conditions as shown in Table 2.

(15)

Accordingly, the capacitance Cdc is obtained fromC dc ==

WC

ωinVC 2 rc
VIN I IN

,

(16)

2

4ωinVC rc

IV.

Therefore the capacitance Cdc depends on the peak-peakvoltage ΔVC.

COMPARISON OF LOSSES

This chapter shows the loss analysis using the circuit
simulator Piece-wise Linear Electrical Circuit Simulation(PLECS). We assume that each winding resistance of theinductor is same as 0.25 Ω. The motor condition is simulated
by ideal current sources. Here, the rated voltage of the motor
specification is generally 200 V. However, in the proposed

In the conventional converters, the DC capacitor voltage
must be sufficiently higher than the maximum input voltage
to control the PI controller stable. Therefore, we assume theratio of the capacitor voltage ripple rc parameter is 2.5%. In

518

converter, the voltage transfer ratio between the input
voltage and the output voltage is less than 0.707 because theprinciple of the converter is a step-down converter.
Therefore the motor rating for the proposed converter ischanged to 141 V.

140

110.7 W
(93.1 %)

120

93.9 W
100 85.3 W 85.4 W (94.1 %)(94.6 %) (94.6 %)80

In order to validate the simulation results, the proposed
converter has been tested practically. The experimental
conditions are the same as the simulation, in Table 1 and 2.
Figure 5 shows operation waveforms of the proposed
converter. Sinusoidal waveforms are obtained on the singlephase input current and three-phase output current, with asingle-phase power factor of over 99 %.

No-load loss
Filter inductor loss
Inverter loss

60
Boost inductor loss
40
PFC converter loss

20

Rectifier loss
0
Proposed Proposed Conventional Conventional
circuitcircuitcircuitcircuit(Experiment)
(CCM)
(DCM)

Figure 6 shows the comparison of the efficiency between
experiments and simulations. The proposed system canachieve efficiency 94.6 % similar to the simulated loss
analysis. Moreover, simulation results of the loss can achieve
approximately the same efficiency to the experimental
results at any range. That is, those experimental results
confirmed that the power loss for each converter can be
discussed based on loss simulations.

Fig.7 Loss analysis of converters.

Figure 7 shows loss comparisons among the three
converters. The total efficiency of the proposed converter isincreased by 0.7 % comparing to the CCM. The largest
difference shown in the loss is the boost inductor loss. DCM
shows the largest in the boost inductor loss because the peakcurrent is the highest among these converters. (Refer toTable 3). In the proposed converter, although the peakcurrent is equal to CCM, the amount of current flows into theboost-up inductor is nearly quarter of the CCM.
Figure 8 shows a study on the losses among the boost
choppers (conventional circuits) and the active buffer(proposed converter). The loss of the active buffer isdecreased by 10 to 20 % in compared with the conventional
boost choppers. In particular, even the number of switches isincreased in the active buffer, but the current passing throughthe active buffer is quarter of the input current. Therefore theconduction loss is decreased.
V.

DESIGN OF CONVERTER VOLUME

A. Inductor
The design of the inductor volume can be calculated byusing an area product method [7]. The area product Ap isdefined as following
Ap = Ae Aw ,Fig.8 Detail loss analysis of PFC converters.

Ae

(17)

where Ae is the cross-sectional area of magnetic core, Aw is
the cross-sectional area of the winding wire as shown Fig. 9.
The area product Ap can obtain the volume due to bisect Aeand Aw at right angles. The volume of an inductor can be
related to the area product Ap. The relationship is derived
according to

D

D

A

B

Aw
A
C
D

Fig.9 Design of core.

519

BFig. 11 Simplified thermal model.

Capacitance [ F]Fig. 10 Relationship between the
inductor volume and the area products.

(a)Volume of capacitor versus capacitance(b) Capacitance versus Rated ripple current(c)Volume of capacitor versus rated ripple current
Fig. 12 Relationship among volume of capacitor, capacitance and rated ripple current.
3

VL = K V A p 4 ,Figure 10 shows the relationship between the inductor
volume and the area products. From (18), (19), the volume of
an inductor is proportional to the three-quarters power of thestored energy in the inductor. In this specification, thevolume of the boost inductor in the active buffer can be
decreased by 70% lower than the standard boost chopper.

(18)

where KV is a constant related to core configuration values.
The area product of an inductor is obtained as
Ap =

2W m
,
K u Bm J w(19)

B. Heat sink
Heat sinks are designed by concerning about the power
density. At first, we calculate the cooling system
performance index (CSPI) [8],[9] as

where Wm, Ku, Bm and Jw are the energy stored in the
inductor, the utilization factor, amplitude of a magnetic flax
density in the core, and the amplitude in the current densityof the winding conductor, respectively.

CSPI =We designed a magnetic ferrite C-core based on thefollowing parameters as shown in Fig.9: Kv = 19.2 (the rated
A : B and C : D is set to 1:3), Ku = 0.5 Bm = 0.8 T and Jw = 4
A/mm2.

1
.
RthVF

(20)

Figure 11 shows a simplified thermal model. Parametersof resistance Rth_j-c and Rth_c-f are obtained from the data sheet.
Rthf is calculated from (20) with loss analysis data.

520

In this paper, the heat sink is designed to meet thefollowing specifications: CSPI = 5, Junction temperature =125 °C, ambient temperature = 40 °C.

800
600

C. Capacitor
The design of the capacitor volume is difficult to indicate
by mathematical expression. Therefore, the capacitor volume
is designed based on the available market products.
Figure 12 presents three different types of capacitor thatcan be utilized as a DC capacitor. As can be seen in Fig.
12(a), the volume of these capacitors is proportional to thecapacitance. The smallest capacitor for the proposed
converter is shown in Fig. 12(a). Notice that the selection of
the electrolytic capacitor must consider upon its rated ripple
current. Therefore, the large capacitor of conventional
converter must select in fig 12(b), and Fig. 12(c).

400Inductor
Capacitor

200

Heat sink0

Input filter
ProposedcircuitConventional Conventional
circuitcircuit
(CCM)
(DCM)

Fig.13 Total volume of passive components
Table 3 Comparison of the conventional CCM, DCM and proposed
converter.

Figure 13 show the total volume of the passives
components implemented in the conventional converters andthe proposed converter. The total volume of the proposed
converter is shown to decrease by 0.6 times in comparedwith the conventional converter. In particular, the volume of
the active buffer, which includes of the boost inductor andthe DC capacitor, can be reduced by approximately 60%
than that of the standard boost chopper.
Table 3 shows the comparison among these converters.
The efficiency of the proposed circuit is higher than theconventional circuits even the amounts of switches are
increased in the proposed circuit. In addition, volume of the
proposed converter is smaller than conventional circuits dueto the decrement on the inductor size.
VI.

[3]

Sangsun Kim; Enjeti, P.N.; “Control of multiple single-phase PFC
modules with a single low-cost DSP” in Industry Applications, IEEE
Transactions, Vol. 39, Issue: 5, 2003 , Page(s): 1379 – 1385.
[4] Shimizu, T. Wada, K. Nakamura, N. " Flyback-Type Single-Phase
Utility Interactive Inverter With Power Pulsation Decoupling on the
DC Input for an AC Photovoltaic Module System " PowerElectronics, IEEE Transactions on Issue Date: Sept. 2006 Volume: 21
Issue: 5, pp. 1264 - 1272, (2006)[5] Kuo-Hen Chao; Po-Tai Cheng; Shimizu, T. “New control methods
for single phase PWM regenerative rectifier with power decoupling
function” Power Electronics and Drive Systems, 2009. PEDS 2009.
International Conference on, pp. 1091 - 1096.
[6] Y. Ohnuma, J. Itoh; “A control method for a single-to-three-phasepower converter with an active buffer and a charge circuit” Energy
Conversion Congress and Exposition (ECCE), 2010 IEEE, pp. 1801 1807.
[7] C. W.T McLyman, “Magnetic Core Selection for Transformer andInductors, 2nd Ed., New York, NY: Marcel Dekker, 1997.
[8] Kazimierczuk, M.K.; Sekiya, H.; “Design of AC resonant inductors
using area product method” Energy Conversion Congress andExposition, 2009. ECCE 2009. IEEE pp. 994 - 1001.
[9] U. Drofenk, G. Laimer, and J. W. Kolar, “Theroretical Converter
Power Density Limits for Forced Convection Cooling” in PCIM
Europe 2005, pp. 608-619.
[10] Kolar, J.W.; Drofenik, U.; Biela, J.; Heldwein, M.L.; Ertl, H.; Friedli,T.; Round, S.D.; “PWM Converter Power Density Barriers” in Power
Conversion Conference - Nagoya, 2007. PCC '07, pp. 9 - 29.

CONCLUSION

This paper compares the efficiency and the volume
between several single-to-three-phase PFC converters. The
efficiency of the proposed converter is highest efficiency andsmallest volume of these converters. In particular, theproposed converter is 1.5% higher than the conventional
converter with DCM. In addition, the total volume of the
proposed converter is reduced by 0.7 times than that of theconventional converter with CCM. Therefore, the converter
can achieve downsizing and high-efficiency by using the
proposed active buffer.
ACKNOWLEDGMENT
This study was supported by Industrial Technology Grant
Program in 2009 from New Energy and Industrial
Technology Development Organization (NEDO) of Japan.
REFERENCES
[1]

[2]

Zhonghui Bing; Min Chen; Miller, S.K.T.; Nishida, Y.; Jian Sun;
“Recent Developments in Single-Phase Power Factor Correction” inPower Conversion Conference - Nagoya, 2007. PCC '07, pp. 1520 1526.
Crebier, J.-C.; Revol, B.; Ferrieux, J.P.; “Boost-chopper-derived PFC
rectifiers: interest and reality” in Industrial Electronics, IEEE
Transactions, Vol. 52, Issue: 1, 2005 , Page(s): 36 – 45.

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