I. INTRODUCTION
Tapped-Inductor Filter Assisted
Soft-Switching PWM DC-DC
Power Converter
SERGUEI MOISSEEV
KOJI SOSHIN
MUTSUO NAKAOKA, Member, IEEE
Yamaguchi University
Japan
A novel high-frequency transformer linked full-bridge
type soft-switching phase-shift pulsewidth modulated (PWM)
controlled dc-dc power converter is presented, which can be
used as a power conditioner for small-scale photovoltaic and
fuel cell power generation systems as well as isolated boost
dc-dc power converter for automotive ac power supply. In these
applications with low-voltage large-current sources, the full-bridge
circuit is the most attractive topology due to the possibility of
using low-voltage high-performance metal-oxide-semiconductor
field-effect transistor (MOSFET) and achieving high efficiency
of the dc-dc power converter. A tapped-inductor filter including
the freewheeling diode is newly implemented in the output stage
of the full-bridge phase-shift PWM dc-dc converter to achieve
soft-switching operation for the wide load variation range.
Moreover, in the proposed converter circuit, the circulating
current is effectively minimized without using additional resonant
circuit and auxiliary power switching devices. The practical
effectiveness of the proposed soft-switching dc-dc power converter
was verified in laboratory level experiment with 1 kW 100 kHz
breadboard setup using power MOSFETs. Actual efficiency of
94—97% was obtained for the wide duty cycle and load variation
ranges.
Manuscript received September 10, 2001; revised June 11, 2004;
released for publication September 16, 2004.
IEEE Log No. T-AES/41/1/844817.
Refereeing of this contribution was handled by M. G. Simoes.
Authors’ address: 2-1-1, Tokiwadai Dept. of Electrical
and Electronics Engineering, Yamaguchi University, Ube
City, Yamaguchi, Japan, Postal Code 755-8611, E-mail:
(sergey@pe news1.eee.yamaguchi u.ac.jp).
c 2005 IEEE
0018-9251/05/$17.00 °
174
A variety of the high-frequency transformer linked
dc-dc converter circuit topologies have been for fuel
cell power generation systems and 42 V automotive
ac power supplies. In these systems with relatively
low input voltage and large input current, due the
capability of reducing power devices voltage and
current peak stresses, lower switching power losses,
and electromagnetic noises, the high-frequency
step-up transformer zero voltage switchings (ZVS)
phase-shifted pulsewidth modulated (PS-PWM)
full-bridge isolated dc-dc power converters have
attracted much attention [1]. However, there is
a large circulating current in the ZVS PS-PWM
full-bridge dc-dc converter. This current flows
through the high-frequency transformer and its
primary side circuit during the freewheeling interval
as a consequence of the PS-PWM control strategy
[2—4]. Due to this current, the conduction power
losses in the ZVS PS-PWM dc-dc converter are
higher compared with those of the hard-switching
PWM dc-dc converter. This problem becomes
especially significant in the dc-dc power converters
with the low-voltage and large-current sources,
like the above mentioned photovoltaic and fuel
cells and automobile batteries. Moreover, in the
conventional ZVS full-bridge dc-dc power converter,
the soft-switching operation is not obtainable for
lagging bridge-leg power metal-oxide-semiconductor
field-effect transistor (MOSFET) due to insufficient
current to charge/discharge lossless snubber
capacitors of these power MOSFETs under the light
load [4—8].
A new full-bridge PS-PWM dc-dc power converter
with ZVS and zero current switching (ZCS) bridge
legs, using the tapped-inductor filter in the output
stage is presented. In the proposed dc-dc converter,
the soft-switching operation range is enlarged to
10%—100% output load. The circulating current is
effectively reduced without using additional resonant
circuit and auxiliary power switching devices. The
36 V input voltage 1 kW-100 kHz prototype circuit
using power MOSFETs is built and tested in the
experiment. Actual efficiency of the proposed dc-dc
converter is achieved 94—97% over the wide duty
cycle and load variation ranges.
II.
PROPOSED SOFT-SWITCHING DC-DC
CONVERTER CIRCUIT
A. Circuit Configuration
Fig. 1 shows a schematic circuit topology of
the proposed high-frequency transformer linked
full-bridge soft-switching PS-PWM dc-dc power
converter with tapped-inductor filter Ld1 =Ld2 in its
output stage. In fact, the full-bridge dc-dc converter
IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 41, NO. 1
JANUARY 2005
Fig. 1. Proposed full-bridge type soft-switching PS-PWM dc-dc
power converter with trapped inductor filter.
is a buck converter, however, the boost characteristic
of the full-bridge dc-dc converter can be achieved by
selecting step-up high-frequency transformer Tr with
suitable turns ratio aT , where aT = np =ns and np and
ns are the primary and secondary windings numbers,
respectively (see Fig. 1).
The lossless-snubber capacitors C1 and C2 in
parallel with leading bridge-leg active semiconductor
devices (power MOSFETs) Q1 (switch S1 /diode
D1 ) and Q2 (S2 =D2 ) make the power MOSFETs
Q1 , Q2 operate with ZVS transitions. The lagging
bridge-leg power MOSFETs Q3 and Q4 operate with
ZCS at turn-on with the aid of the inductance Ls . This
inductance Ls can be presented by leakage inductance
of the high-frequency transformer Tr. On the other
hand, the tapped-inductor filter Ld1 =Ld2 including
a freewheeling diode is used to obtain ZCS for the
power MOSFETs Q3 and Q4 at turn-off as well as to
minimize circulating current during the freewheeling
interval.
B. Circuit Operation
Fig. 2 illustrates switching-pulse sequences and
theoretical voltage and current waveforms of the
presented dc-dc converter in a steady state. The
switches S1 and S2 are driven complementary with
the short blanking interval td to protect circuit from
shorting and to achieve ZVS commutation at the
turn-on instant. The output voltage E0 is regulated
by shifting the gate-pulse of the lagging bridge-leg
switches from gate-pulse of the leading bridge-leg
switches and thus varying the interval ton (ton = DT=2)
as phase-shifted PWM control strategy with the
constant switching frequency f = 1=T.
The operating principle of the proposed dc-dc
converter circuit under the steady-state condition can
be described as follows. The main operation mode
during a half period of the steady state operation is
shown in Fig. 3.
Fig. 2. Calculated waveforms of proposed soft-switching
PS-PWM dc-dc power converter.
Mode 1 (t < t0 ): Before time t0 , it is assumed that
the switches S1 , S4 and the rectifier diodes D5 , D8 are
conducting.
Mode 2 (t0 , t1 ): At the instant t0 , the switch
S1 (Q1 ) is turned off under principle of ZVS with
the aid of the lossless-snubber capacitors C1 and C2
(C1 = C2 = C). The voltage vQ1 across the switch
S1 (Q1 ) rises as follows,
dvQ1 (t) im (t0 ) + iD5 (t0 )=®T
=
:
(1)
dt
2C
After that, the rectified voltage vd decreases in
accordance with the following equation,
vd (t) =
(E ¡ vQ1 (t))
:
®T
(2)
The freewheeling diode D9 starts to conduct
when vd reaches the certain value ®L E0 , where ®L
is the turns ratio of the tapped-inductor defined as
®L = n2 =(n1 + n2 ); n1 , n2 are the number of turns of
MOISSEEV ET AL.: TAPPED-INDUCTOR FILTER ASSISTED SOFT-SWITCHING PWM DC-DC POWER CONVERTER
175
Fig. 3. Equivalent circuits during half period of steady state operation.
Ld1 and Ld2 , respectively. The rectifier current
id5 decreases and it is expressed by the following
equation,
diD5 (t)
®2 ® E
=¡ T L 0:
dt
LS
(3)
Mode 3 (t1 , t3 ): Due to the presence of the leakage
and magnetizing inductances in the transformer Tr its
primary side diode D2 becomes forward biased and,
therefore, starts to conduct. After the rectified current
id5 reaches zero at the instant t1 , the freewheeling
current i1 becomes equal to the magnetizing current of
the high frequency transformer Tr. The whole output
current flows through D9 , Ld2 and Ld1 .
At the instant t2 , pulse signal vg2 is applied to the
switch S2 or Q2 . The switch S2 is turned on with
ZVS. The circulating current i1 flows through the
transformer Tr and its primary side circuit consisted
of the diode D2 and the switch S4 .
This interval ends when the switch S4 is turned off
with ZCS at the instant t3 .
Mode 4 (t4 , t5 ): At the instant t4 , the switch S3 is
turned on with ZCS due to the effect of the leakage
inductance LS . The current through the switch S3 rises
as shown by the following equation,
diQ3
E ¡ E0 ®T ®L
:
¼
dt
LS
(4)
The output current reflected to the primary side of
the transformer flows through the switches S2 (Q2 )
and S3 . On the other hand, the current iD9 through Ld2
and D9 decreases and the diode D9 turns off.
176
During Mode 4, the energy is being delivered
through the switches S2 , S3 , and high-frequency
transformer Tr, and rectifier diodes D6 , D7 . The half
cycle of operation ends at the instant t5 .
The operation during the next half-cycle is
symmetrical with the mentioned one half-cycle.
In the proposed dc-dc converter, the switches
S1 (Q1 ) and S2 (Q2 ) are turned on and turned
off with ZVS, while the switches S3 and S4
operate with ZCS at turn-on and turn-off.
The circulating current during freewheeling
interval t0 ¡ t3 (see Fig. 2) is substantially
lowered without using any additional auxiliary
resonant snubber circuits or active semiconductor
devices.
III. OUTPUT VOLTAGE CHARACTERISTICS AND
TAPPED-INDUCTOR TURNS RATIO DESIGN
The tapped-inductor filter Ld1 =Ld2 including
freewheeling diode D9 acts as a passive voltage clamp
element in the proposed soft-switching PS-PWM
dc-dc converter, so that the rectified output voltage
vd is clamped to the positive polarity during the
freewheeling interval (t0 ¡ t3 ). Therefore, the rectifier
diode D5 (D6 ) becomes reverse biased, and the output
current flows through the secondary side freewheeling
diode D9 during the freewheeling interval. As a result,
the circulating current i1 through the transformer and
its primary side circuit is effectively reduced. Fig. 4
shows the rectified voltage vd and rectified current iD5
theoretical waveform.
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JANUARY 2005
Fig. 4. Operating waveforms of rectified voltage vd and rectified
current iD5 .
During a half-cycle period, the rectified voltage vd
is expressed by,
vd = NL E0
vd =
E
NT
for
for
t0 < t · t4
t4 < t · t5 :
(5)
The output voltage characteristic of the proposed
dc-dc power converter can be represented by the
following expression,
E0 =
DE
Ls I0
:
¡
®T f1 ¡ ®L (1 ¡ D)g ®2T Th f1 ¡ ®L (1 ¡ D)g2
(6)
To make the average output voltage E0
characteristic independent of the output current
I0 , and to obtain effective cancellation of the
circulating current, the leakage inductance Ls of the
high-frequency transformer Tr is designed as small as
possible.
The design of the tapped-inductor Ld1 =Ld2 turns
ratio is made on the basis of the simulation results
under the closed loop control scheme. The simulated
waveforms of the transformer primary side current
i1 , inductor Ld1 current iLd1 , and rectified voltage vd
are shown in Fig. 5. To achieve effective circulating
current minimization and, at the same time, to
prevent the increase of the output current ripples,
the tapped-inductor turns ratio is set to 0.3 for dc-dc
converter designed for 100 kHz operating frequency.
IV. EXPERIMENTAL RESULTS
To verify the operating principle and steady
state performances, the experiment was carried out
with a 1 kW 100 kHz prototype circuit. To achieve
high efficiency and high performances of the dc-dc
converter, power MOSFETs were selected as the
active semiconductor devices. The power circuit
components parameters are indicated in Table I. The
three series-connected 12 V automobile batteries
Fig. 5. Calculated results under closed loop control.
(a) Waveforms of transformer primary side current i1 .
(b) Waveforms of filter inductor Ld1 current ild1 .
(c) Waveforms of the recified voltage vd .
Fig. 6. External appearance of tapped inductor.
were used as 36 V dc power supply for the tested
dc-dc converter. To reduce conduction power losses
in the high-frequency inverter stage of the proposed
converter, 2 power MOSFETs were connected in
parallel. Fig. 6 demonstrates the external appearance
of the tapped inductor Ld1 , Ld2 , which was used in the
experiment.
Fig. 7 illustrates the experimental results of the
tested dc-dc converter under a condition of 50% full
load. The measured voltage and current waveforms
of the high-frequency transformer Tr and power
MOSFET Q4 , gate-pulse voltage of the power
MOSFET Q2 , and voltage across this device are
presented in Fig. 7(a), (b), and (c), respectively.
Observing waveforms of Fig. 7(a), it can be
concluded that the circulating current is substantially
MOISSEEV ET AL.: TAPPED-INDUCTOR FILTER ASSISTED SOFT-SWITCHING PWM DC-DC POWER CONVERTER
177
TABLE I
Design Specifications and Circuit Parameters
Item
Symbol
Value
Input Voltage
Ein
36 V
Operating frequency
f
100 kHz
MOSFETs
Q1 ¡ Q4
2SK3228, VDS = 80 V,
RDS = 0:006 −,
IDS = 75 A
(2 switches in parallel)
Diodes
D 5 ¡ D8
FML33S
VRRM = 300 V,
IO = 20 A
Lossless snubber capacitors
C1 , C2
25 nF
Transformer turns ratio
®T
1:4
Magnetizing inductance
Lm
70 ¹H
Leakage inductance
LS
300 nH
Tapped inductor
Ld1 , Ld2
Ld1 = 50 ¹H,
Ld2 = 13 ¹H
Core: Ferrite PQ 50/50
Tapped inductor turns ratio
®L
0.3
Output capacitor
Cd
250 ¹F
Fig. 8. Output Eo and input voltage E characteristic as function
of output current Io.
Fig. 7. Experimental results. E = 36 V, Eo = 110 V, Io = 5 A,
D = 0:65. (a) High frequency transformer voltage vab and current
i1 waveforms. Scale: v: [20 V/div], i: [20 A/div], time: [2 ¹s/div].
(b) MOSFETs Q4 voltage vQ4 and current iQ4 waveforms.
Scale: v: [20 V/div], i: [10 A/div], time: [2 ¹s/div].
(c) Gate signal voltage vg2 and voltage vQ2 across MOSFETs Q2
waveforms. Scale: vg2 : [10 V/div], vQ2 : [20 V/div],
time: [2 ¹s/div].
lowered without using any additional resonant or
active auxiliary snubber circuits. Moreover, as shown
in Fig. 7(b) and (c), the power MOSFET Q4 operates
with ZCS at turn-on and turn-off, while the power
MOSFETs Q2 turns off and turns on with ZVS. The
soft-switching conditions for the lagging bridge leg
power MOSFETs Q3 and Q4 were obtained from no
load to full load. The ZVS operation ranges for the
power MOSFETs Q1 and Q2 of the leading bridge
legs were realized from 10% to 100% load.
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Fig. 9. Actual efficiency and total power losses as function of
load current I0 .
The output voltage characteristics Eo of the
proposed dc-dc power converter as a function of the
output current Io under the different duty cycle values
D = 0:5—0.7 are shown in Fig. 8.
Fig. 9 demonstrates the measured actual efficiency
and the total power losses as functions of the output
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JANUARY 2005
current Io under the duty cycle values D = 0:5—0.7.
The actual efficiency 94—97% was achieved over the
wide duty cycle and load variation ranges.
V. CONCLUSIONS
The new high-frequency transformer linked
full-bridge type soft-switching PS-PWM controlled
dc-dc power converter with ZVS and ZCS bridge-legs
was presented in this paper for the low-voltage
and large-current input side power supplies.
The generation of the conduction losses due to
circulating current during freewheeling period was
suppressed by using tapped inductor filter including
freewheeling diode. The high-efficiency stable
soft-switching operation ability of the proposed dc-dc
power converter was verified on the basis of the
experimental results using 1 kW 100 kHz breadboard
circuit using low-voltage high-performance power
MOSFETs. The proposed soft-switching dc-dc
power converter has enough ability to be used
as high performance isolated type dc-dc power
conditioner for 1 kW class photovoltaic or fuel
cell power generation systems and for step-up
isolated dc-dc converter of automotive ac power
supply.
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Patterson, O. D., and Divan, D. M.
Pseudo-resonant full bridge DC/DC converter.
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[8]
Kim, E. S., Joe, K. Y., Key, M. H., Kim, Y. H., and Yoon,
B. D.
An improved soft-switching PWM FB DC/DC converter
for reducing conduction losses.
IEEE Transactions on Power Electronics, 14, 2 (1999),
258—263.
Cho, J. G., Back, J. W., Jeong, C. Y., Yoo, D. W., and Joe,
K. Y.
Novel zero-voltage and zero-current-switching full bridge
PWM converter using transformer auxiliary winding.
IEEE Transactions on Power Electronics, 15, 2 (2000),
250—257.
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Moisseev, S., Hamada, S., Ishitobi, M., Hiraki, E., and
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MOISSEEV ET AL.: TAPPED-INDUCTOR FILTER ASSISTED SOFT-SWITCHING PWM DC-DC POWER CONVERTER
179
Serguei Moisseev was born in Arsenyev (Primorye), Russia in 1977. He received
the B.Eng. in electro-mechanical engineering from Far-East State Maritime
Academy, Vladivostok, Russia in 2000. He received the M.Eng. degree from
the Department of Electrical and Electronics Engineering, Yamaguchi University,
Japan in 2002.
He is currently a Ph.D. candidate student of Division of Systems Engineering,
the Graduate School of Science and Engineering, Yamaguchi University, Japan.
His research interests include soft-switching high-frequency PWM dc-dc
converters for high power applications.
Mr. Moisseev is a student member of the IEE Japan.
Koji Soshin received his M.Sc.Eng. from the Electronic Engineering Department,
the Graduate School of Electrical and Electronics Engineering,. Kobe University,
Kobe, Japan.
He is now a Ph.D. candidate student in the Graduate School of Science and
Engineering, Yamaguchi University, Yamaguchi, Japan. He joined Matsushita
Electric Works, Ltd. in 1979. He is interested in stepping motor applications,
vector controlled inverter for the induction motor and power electronic circuits
and systems technologies. He is now working in the power supplies for electric
vehicles.
Mr. Soshin is a member of the Japan Society of Power Electronics.
Mutsuo Nakaoka (M’83) received his Ph.D. degree in electrical engineering from
Osaka University, Osaka, Japan in 1981.
He joined in the Electrical and Electronics Engineering Department, Kobe
University, Kobe, Japan in 1981. Since 1995, he has been a professor in the
Electrical and Electronics Engineering Department, the Graduate School of
Science and Engineering, Yamaguchi University, Yamaguchi, Japan. His research
interests include circuit and control systems of power electronics, especially in
soft-switching areas.
Dr. Nakaoka is a member of the Institute of Electrical Engineers of Japan, the
Institute of Electronics, Information and Communication Engineers of Japan, the
Institute of Illumination Engineering of Japan.
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