THREE-PHASE SINGLE STAGE AC-DC BUCK-BOOST CONVERTER
OPERATING IN BUCK AND BOOST MODES
◊
Altamir Ronsani Borges◊ and Ivo Barbi*
Department of Electrical and Telecommunications Engineering: University of Blumenau (FURB)
Blumenau – SC - Brazil
arb@furb.br
*Power Electronic Institute (INEP): Federal University of Santa Catarina (UFSC)
Florianópolis – SC – Brazil
ivobarbi@inep.ufsc.br
Abstract – This paper presents a single stage three
phase Buck-Boost AC-DC converter operating in
continuous conduction mode (CCM). The converter
operates with high power factor in wide input voltage
range (60 – 140 VRMS line-to-neutral). It has three
operations modes: Buck, Boost and a combination of
both, named Buck+Boost. The original topology,
operation stages, mains waveforms and equations for
Buck and Boost modes are presented. Simulation
results for a 1.5 kW , 150 V output voltage converter
are also show.
Keywords – Three-phase AC-DC converter, BuckBoost, power factor correction.
I. INTRODUCTION
The three-phase AC-DC converters evolution is
remarkable, comparing the first diode based structures
with the current ones. Several factors contributed to this
development, such as semiconductor and microelectronics
progress. The creation and adoption of standards for
regulating the electrical equipments interferences in the
power grid, such as IEEE-519, IEC-555, IEC-6100-3-2
and IEC-6100-3-4 [1], also had an important influence as
lead to increased research efforts in the area.
A wide variety of three-phase AC-DC converter
topologies was developed, aimed to comply with the most
varied and stringent specifications [2-6]. Some of them
have been highlighted as the Boost and Buck converters
[3].
Other converters, in spite of their interesting features,
have few references in the literature. This is the case of the
Buck-Boost converters, even presenting a step up/down
output voltage characteristic, has not received considerable
attention [7-10].
The main Buck-Boost three-phase topologies found in
literature are [2, 5]:
• Association of Buck-Boost single-phase modules;
• Converters with two stages of power processing;
• Converters with single stage of power processing;
In [11] is proposed a topology based on three
Buck+Boost single phase modules association, while in
[12] is proposed a topology associating ĆUK single phase
converter modules. The main advantage of this
configuration is that single phase PFC techniques can be
used directly, with a little additional development effort
[2].
978-1-4577-1646-1/11/$26.00 ©2011 IEEE
A two stages converter has its input currents controlled
by a structure, while output voltage regulation is controlled
by another [2].
In [10] two configurations of bidirectional two stages
three-phase Buck-Boost converters are presented. The first
is named ĆUK-ĆUK converter and the second consists of
a SEPIC converter input stage, coupled with a ZETA
converter output stage. An unidirectional structure
composed by a three-phase Buck PFC converter cascaded
with a DC/DC Boost converter is presented in [13, 14]. A
converter formed by a VIENNA Boost PFC rectifier on the
input stage and a DC/DC three-level Buck on the output
stage, is presented in [15].
A single stage converter has its input currents and
output voltage regulation controlled by same structure [2].
The single-stage topologies found in literature are
derived from DC/DC converters with step up/down
features. Boost-Buck converter (ĆUK) is the basis for the
converter discussed in [8]. A topology based on BuckBoost converter is presented in [9], while in [7], a SEPIC
derived converter is proposed.
II. THE PROPOSED CIRCUIT
A. The original single-phase circuit
The proposed circuit is based on the Buck+Boost
single-phase PFC converter, presented in [7]. The basic
configuration is shown in Fig. 1 (the input filter was
omitted).
Fig. 1. Buck+Boost single phase PFC.
For the attainment of the three-phase version of the
circuit, some changes were carried out in the single-phase
topology. As shown in Fig. 2, switch S1 is incorporated to
the rectifier circuit along with the diodes D1 and D2;
inductor L is divided into two equal inductors (L1 and L2)
and the D8 diode is added to the structure.
The voltage source VO represents the association of the
output capacitor with the resistive load, as depicted in Fig.
1. The three-phase rectifier circuit is obtained through a
single-phase module for each phase, connected in wye, as
presented in Fig. 3.
176
+
described strategy, its switches are turned on throughout
the sector.
Three modulators (one per phase) compose by two
superposed saw-tooth waves and two comparators, are
used, as shows Fig. 5.
(a)
(b)
Fig. 2. (a) Switch S1 is incorporated to the rectifier circuit; (b)
Final single-phase module.
Fig. 5: Carriers wave forms and modulator circuit.
IV. OPERATION MODES
The operating regions are defined as the ratio of output
voltage and the line-to-line voltage input - VAB (t) and VAC
(t) for sector 3.
V
Boost Mode: O >1
VP
VO 1
<
VP 2
Buck Mode:
Buck+Boost Mode:
1 VO
<
<1
2 VP
Where VP is the line-to-line voltage peak .
Fig. 3. Final circuit of three-phase Buck-boost PFC converter.
In the circuit of Fig. 3, switches S1A, S1B and S1C are
named Buck switches, while S2A, S2B and S2C are called
Boost switches. All switches are IGBT-type.
III. MODULATION STRATEGY
As a three wire topology is been studied, the input
currents meet the relationship defined in (1):
(1)
IA + IB + IC = 0
Thus, controlling two phases, the third is automatically
defined. In order to implement this strategy, the periods in
which the current of each phase is indirectly controlled
were defined. It was done by dividing the grid voltage
period into sectors, as shown in Fig. 4.
Table I shows the expressions of the static gain for each
phase along the sector 3, for the three operation modes.
TABLE I
Static gains for Buck, Boost and Buck+Boost converter
operation modes
BUCK
BUCK+BOOST
BOOST
⎛ VO 1 ⎞
< ⎟
⎜
⎝ VP 2 ⎠
⎛ 1 VO
⎞
< 1⎟
⎜ <
⎝ 2 VP
⎠
⎛ VO
⎞
> 1⎟
⎜
⎝ VP
⎠
VO
= d j (t)
Vij (t)
VO
= d j (t)
Vij (t)
VO
1
=
Vij (t) 1 − d j (t)
VO
= d k (t)
Vik (t)
VO
1
=
Vik (t) 1 − d k (t)
VO
1
=
Vik (t) 1 − d k (t)
Where i, j and k correspond to phases A, B or C, such that
ViN (t) > VjN (t) > VkN (t) .
V. OPERATION STAGES
Fig. 4: Sectors definition.
In each sector, the phase with higher absolute value is
submitted to indirect control. In order to enable the
Only Buck and Boost modes are discussed in this paper.
The Buck+Boost is a composite of previous modes, which
one phase operates in Buck mode while another in Boost
mode. Fig. 6 presents the pulse generation schemes for
Buck and Boost switches of one phase, considering the
operation on Buck and Boost modes, respectively.
177
Table II presents the switches command signals for the
three operation modes (Buck, Boost and Buck+Boost) in
sector 3.
In Fig. 7, the pulses applied to switches and the
behavior of parameters that define the operation stages for
Buck and Boost modes are outlined.
Fig. 7: Waveforms outline for parameters that define the Buck
and Boost modes operation stages.
Fig. 6. Pulses generation for Buck and Boost switches.
TABLE II
Command signals for each mode of operation.
BUCK
BOOST
BUCK + BOOST
S1A
1
1
1
S2A
1
1
1
S1B
S2B
0
1
0
S1C
S2C
0
1
1
Where:
1
0
=
=
Switch turned on;
Switch turned off;
=
Switch that receives command pulses.
On the Table III the ranges that define the stages, valid
for both operation modes, are shown
TABLE III
Ranges of operation stages.
STAGE
1
2
3
INTERVAL
t0 – t1
t1 – t2
t2 – t3
STAGE
4
5
INTERVAL
t3 – t4
t4 – t0
A. Operation Stages –Buck Mode
This operation mode comprises five steps, whose limits
are defined by interval t0 to t4, according to shown in Fig.
7.
• t0: D4A is blocked by extinction of it current;
• t1: S1B is turned off;
• t2: S1C is turned off;
• t3: The currents of L1B and L1C are extinct;
• t4: A new switching cycle is started with S1B and S1C
turned on.
Buck mode operation introduces an input current
discontinuity, requiring the use of an input filter. An
typical LC filter per phase was employed, whose design
was based on [16].
B. Operation Stages –Boost Mode
This operation mode comprises five steps, whose limits
are defined by interval t0 to t4, as shown in Fig. 7.
• t0: D4A is blocked by extinction of it current;
• t1: S2B is turned off;
• t2: S2C is turned off;
• t3: A new switching cycle is started with S2B and S2C
turned on;
• t4: D7C and D8B are blocked by the extinction of it
current.
In Fig. 8 and Fig. 9, the configurations assumed by the
converter operating in Buck and Boost modes,
respectively, are presented.
VI. EXPERIMENTAL RESULTS
In order to validate the theoretical analysis, a prototype
with the following features was implemented:
• Input line-to-neutral voltage range: 60 to 140 VRMS;
• Output voltage: 150 V;
• Switching frequency: 39600 Hz;
• Output power: 1500 W.
For this input voltage range, the converter operates in
the modes shown in the Table IV.
TABLE IV
Ranges of operation modes
Input voltage range (VRMS)
60 to 80
80 to 127
Above 127
Operation mode
Boost
Buck+Boost
Buck
The values of THD and power factor were obtained
with the software WaveStar version 2.8.1.
178
Fig. 8: Buck mode operation stages.
Fig. 9: Boost mode operation stages.
179
Figure 10 depicts the waveforms for three input currents
(IA, IB and IC) on Boost operation mode. The total harmonic
distortion (THD) of these currents, varies between 3,9% (IA)
and 5% (IC).
IA
IB
IC
Fig. 12: Boost mode: inductors L1A and L2A currents waveforms.
IA = 31. 01 AP-P
Fig. 10: Boost mode: input currents waveforms.
In Figure 11 the line-to-neutral voltage VAN and IA current
are presented, where it can be observed the high power factor
in the boost mode (0.997).
Fig. 11: Boost mode: Line-to-neutral VAN and input current IA
waveforms.
The inductors L1A and L2A currents waveforms are shown
in Figure 12. In each phase, the current of these inductors is
equal and corresponds to the rectified input current.
In Figure 13 the waveforms of voltage VAN (CH1), the
signal that indicates the sectors 3, 4, 9 and 10 (CH2), and the
voltage across the switch S2A (CH4) are presented. Through
the waveform of CH4 is possible to prove that the voltage
across the boost switch has de same magnitude of the load
voltage (166 V).
Fig. 13: Boost mode: Line-to-neutral VAN (CH1); signal that
indicates the sectors 3, 4, 9 and 10 (CH2) and voltage across the
switch S2A (CH4).
Figure 14 depicts the three unfiltered input currents (IA, IB
and IC) waveforms on Buck operation mode.
180
Fig. 14: Buck mode: unfiltered input currents waveforms.
Fig. 16: Buck mode: Line-to-neutral VAN and filtered input current
IA waveforms.
Figure 15 shows the three filtered input currents
waveforms (IA, IB and IC). The harmonic distortion of these
currents varies between 5.7% (IA) and 6.1% (IC).
Fig. 17: Buck mode: inductors L1A and L2A currents waveforms
(CH3 and CH2, respectively) and line-to-neutral VAN (CH4).
Fig. 15: Buck mode: filtered input currents waveforms.
In Figure 16 the line-to-neutral voltage VAN and the
filtered IA current in Buck mode are presented, where it can
be observed the high power factor in this mode (0.974).
In Figure 17 are shown the inductors L1A and L2A currents
waveforms (CH3 and CH2, respectively) and line-to-neutral
VAN (CH4).
In Figure 18 are presented the waveforms of S2A
command signal (CH1) and voltage across the switch S2A
(CH3). Through the waveform of CH3 is possible to observe
that the voltage across the boost switch has de same
magnitude of the line-to-line input voltage (376 V peak).
Figure 18: Buck mode: Voltage across the switch S2A (CH3) and
S2A command signal (CH1).
181
VII. CONCLUSION
From experimental results, it can be seen that the circuit
present high power factor in both Buck and Boost operation
modes.
The proposed topology efficiency varies with the
operating mode: 74% for Boost mode and 87% for Buck
mode, at rated power. Large part of this low efficiency is
explained by the high voltage drop across the diodes. Diodes
with lower voltage drop are being selected to increase
efficiency.
On the other hand, as the focus of the design was not to
optimize the efficiency but only to prove the theoretical
analysis of the structure, these results can be improved.
The current distortion observed in Buck mode is due to
unbalance and distortion of input voltages. Alternatives to
reduce the influence of these factors on the input current are
being studied.
[10]
[11]
[12]
[13]
VIII. REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Key, T. S.; Lai, J. S., "Comparison of standards
and power supply design options for limiting
harmonic distortion in power systems", IEEE
Transactions on Industry Applications, vol. 29, n°. 4,
pp. 688-695, 1993.
Hengchun, M.; Lee, C. Y.; Boroyevich, D. et al.,
"Review of high-performance three-phase powerfactor correction circuits", IEEE Transactions on
Industrial Electronics, vol. 44, n°. 4, pp. 437-446,
1997.
Singh, B.; Chandra, A. et al., "A review of threephase
improved
power
quality
AC-DC
converters", IEEE Transactions on Industrial
Electronics, vol. 51, n°. 3, pp. 641-660, 2004.
Erickson, R. W., "Some Topologies of High
Quality Rectifiers", First International Conference
on Energy, Power, and Motion Control, Tel Aviv,
1997.
Shah, J.; Moschopoulos, G., "Three-phase
rectifiers with power factor correction", Canadian
Conference on Electrical and Computer Engineering,
2005, vol., pp. 1270-1273, 2005.
Bhat, A. H.; Agarwal, P., "Three-phase, power
quality improvement ac/dc converters", Electric
Power Systems Research, vol. 78, n°. 2, pp. 276-289,
2008.
Shieh, J. J., "SEPIC derived three-phase switching
mode rectifier with sinusoidal input current", IEE
Proceedings-Electric Power Applications, vol. 147,
n°. 4, pp. 286-294, 2000.
Ching-tsai, P.; Jenn-jong, S., "A single-stage threephase boost-buck AC/DC converter based on
generalized zero-space vectors", IEEE Transactions
on Power Electronics, vol. 14, n°. 5, pp. 949-958,
1999.
Pires, V. F.; Silva, J. F. A., "Single-stage threephase buck-boost type AC-DC converter with high
power factor", IEEE Transactions on Power
Electronics, vol. 16, n°. 6, pp. 784-793, 2001.
[14]
[15]
[16]
Kikuchi, J.; Lipo, T. A., "Three phase PWM boostbuck
rectifiers
with
power
regenerating
capability", Industry Applications Conference, 2001.
Thirty-Sixth IAS Annual Meeting. Conference Record
of the 2001 IEEE, vol. 1, pp. 308-315 vol.1, 2001.
Ridley, R.; Kern, S.; Fuld, B., "Analysis and design
of a wide input range power factor correction
circuit for three-phase applications", Applied
Power Electronics Conference and Exposition, 1993.
APEC '93. Conference Proceedings 1993., Eighth
Annual, vol., pp. 299-305, 1993.
Kamnarn, U.; Chunkag, V., "Analysis and Design
of a Modular Three-Phase AC-to-DC Converter
Using ĆUK Rectifier Module With Nearly Unity
Power Factor and Fast Dynamic Response", IEEE
Transactions on Power Electronics, vol. 24, n°. 8, pp.
2000-2012, 2009.
Nishida, Y.; Miniboeck, J.; Round, S. D. et al., "A
New 3-phase Buck-Boost Unity Power Factor
Rectifier with Two Independently Controlled DC
Outputs", Applied Power Electronics Conference,
APEC 2007 - Twenty Second Annual IEEE, vol., pp.
172-178, 2007.
Baumann, M.; Drofenik, U.; Kolar, J. W., "New
wide input voltage range three-phase unity power
factor rectifier formed by integration of a threeswitch buck-derived front-end and a DC/DC boost
converter output stage", Telecommunications
Energy Conference, 2000. INTELEC. Twenty-second
International, vol., pp. 461-470, 2000.
Nussbaumer, T.; Kolar, J. W., "Comparison of 3Phase Wide Output Voltage Range PWM
Rectifiers", IEEE Transactions on Industrial
Electronics, vol. 54, n°. 6, pp. 3422-3425, 2007.
Vlatkovic, V.; Borojevic, D.; Lee, F. C., "Input
filter design for power factor correction circuits",
International Conference on Industrial Electronics,
Control, and Instrumentation, 1993. Proceedings of
the IECON '93., vol., pp. 954-958 vol.2, 15-19 Nov
1993, 1993.
182