IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008
793
A Novel Zero-Voltage-Switching
PWM Full Bridge Converter
Wu Chen, Student Member, IEEE, Xinbo Ruan, Senior Member, IEEE, and Rongrong Zhang
Abstract—Introducing resonant inductance and clamping
diodes into the full-bridge converter can eliminate the voltage
oscillation across the rectifier diodes and increase the load range
for zero-voltage-switching (ZVS) achievement. The resonant
inductance is shorted and its current keeps constant when the
clamping diode is conducting, and the clamping diode is hard
turned-off, causing significant reverse recovery loss if the output
filter inductance is relatively larger. This paper improves the
full-bridge converter by introducing a reset winding in series with
the resonant inductance to make the clamping diode current decay
rapidly when it conducts. The reset winding not only reduces the
conduction losses, but also makes the clamping diodes naturally
turn-off and avoids the reverse recovery. The operation principle
of the proposed converter is analyzed. The design of the turns
ratio of transformer is discussed. A 1 kW prototype converter is
built to verify the operation principle and the experimental results
are also demonstrated.
Index Terms—Clamping diodes, full bridge converter, reset
winding, zero-voltage-switching (ZVS).
I. INTRODUCTION
T
HE full-bridge converter is widely used in medium-to-high
power dc–dc conversions because it can achieve
soft-switching without adding any auxiliary switches. The
soft-switching techniques for PWM full bridge converter can
be classified into two kinds: one is zero-voltage-switching
(ZVS) and the other is zero-voltage and zero-current-switching
(ZVZCS) [1]. The leakage inductance of the transformer and
the intrinsic capacitors of the switches are used to achieve
ZVS for the switches. The ZVS characteristics are load dependent and will be lost at light load [2]–[6]. In ZVZCS PWM
full-bridge converters, one leg achieves ZVS, and the other
leg achieves ZCS [7]–[13]. However, there is serious voltage
oscillation across the rectifier diodes caused by the reverse
recovery no matter ZVS or ZVZCS is realized for the switches.
In order to overcome this problem, Redl et al. [14]–[16] introduced a resonant inductance and two clamping diodes into
the primary side of transformer. The solution eliminates the
voltage ringing and overshoot, thus the voltage stress of the
Manuscript received April 25, 2007; revised July 23, 2007. This work was
supported by the College Young Teachers Fund of Fok Ying Tung Education
Foundation under Award 91058 and by the Delta Power Electronics Science
and Education Development Fund. Recommended for publication by Associate
Editor M. Vitelli.
The authors are with the Aero-Power Sci-Tech Center, College of Automation Engineering, Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China. (e-mail: chenwu@nuaa.edu.cn; ruanxb@nuaa.edu.cn;
zhangrongrong xin@163.com).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPEL.2007.915764
rectifier diodes is reduced, and without introducing losses or an
additional controlled power device. The difference between the
two locations of the resonant inductance and the transformer
was analyzed and an optimal position was presented. Ruan
et al. [17] analyzed the issue in detail and also observed the
effects of the blocking capacitor in different positions, and a
best scheme was determined.
No matter what the positions of the transformer and the resonant inductance are, the resonant inductance is clamped and its
current keeps constant when the clamping diodes conduct. The
output filter inductance must had enough current ripple so that
the clamping diodes turn off naturally, otherwise the clamping
diodes will be forced to be turned off, resulting in serious reverse recovery.
In this paper, an auxiliary transformer winding is introduced
to the ZVS PWM full-bridge converter to be in series with the
resonant inductance. The introduced winding not only makes
the clamping diode current decay rapidly and reduces the primary side conduction losses, but also can makes the current
ripple of the output filter be smaller; hence the output filter capacitor can be reduced. The winding plays the role of forcing
the clamping diode current to decay to zero, so it is called reset
winding.
The operation principle of the proposed converter will be discussed in Section II. Section III gives the comparisons between
the full-bridge converters with/without reset winding. The experimental results are presented in Section IV to verify the validity of the proposed converter.
II. OPERATION PRINCIPLE
The proposed ZVS PWM full-bridge converter with reset
winding is shown in Fig. 1, where
is the introduced reset
winding. The popular phase-shifted control is used for the
and
form the leading leg and
and
converter where
form the lagging leg. The converters in Fig. 1(a) and (b) are
defined as
type and
type, respectively, since the
is connected with the lagging leg and
primary winding
the leading leg, respectively. The operation principle of the two
types is similar and the difference is the same as described in
type
[17], i.e., the clamping diodes conduct only once in
type. The following description
while conduct twice in
type.
will be focused on the
The key waveforms of the ZVS PWM full-bridge converter
with/without reset winding are shown in Fig. 2. The full-bridge
converter without reset winding was analyzed in detail in [17],
so the operation principle of the converter with reset winding is
analyzed as follows.
To simplify the analysis, the following assumptions are made.
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794
Fig. 1. Proposed ZVS PWM full bridge converter.(a)
type.
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008
type. (b)
1) All the switches and diodes are ideal, except for the rectifier
diode, which is equivalent to an ideal diode and a paralleled
capacitor to simulate the reverse recovery.
2) All the capacitors, inductance and transformer are ideal.
3) The turns ratio of the transformer is the primary winding:
.
the reset winding: the secondary winding
Fig. 3 shows the equivalent circuits of the switching stages in
a half period. The second half period is similar to the first half
period.
[Refer to Fig. 3(a)]
1) Stage 1
Prior to , the power is transferred from the input source
to the load through
and
.
is turned off
at zero voltage due to
and
limit the rising rate of
the voltage across . The resonant inductance current
charges
and discharges , and the potential voltage of
is
point decays. In the meanwhile, the capacitor
discharged. As the potential voltage of point is greater
is reverse biased. The voltage of
dethan zero,
conducts naturally.
creases to zero at and
[Refer to Fig. 3(b)]
2) Stage 2
can be turned on at zero voltage when
conducts.
continues to be discharged since the voltage of point
is still higher than zero.
and continue decaying.
and the voltage of
This stage finishes when
point reduce to zero correspondingly.
[Refer to Fig. 3(c)]
3) Stage 3
and
conduct simultaneously, clamping the secis equal to , and the circuit
ondary voltage at zero.
operates in free-wheeling mode.
[Refer to Fig. 3(d)]
4) Stage 4
is turned off at zero voltage at , and
is charged and
is discharged in a resonant manner. This stage finishes
when
rises to
and
falls to zero at .
[Refer to Fig. 3(e)]
5) Stage 5
conducts naturally when
decays to zero, and
can be turned on at zero voltage.
is equal to , and both
Fig. 2. Key waveforms of ZVS PWM full-bridge converters. (a) Without reset
winding. (b) With reset winding.
of them decay linearly with the rate of
. At
and cross zero, and continue increasing linearly in the
negative direction. The load current flows through both the
and reach the reflected filter
rectifier diodes. At
turns off.
inductance current, and
[Refer to Fig. 3(f)]
6) Stage 6
resonates with
after , and
is charged in
continue increasing. At ,
a resonant manner. and
rises to 2
, and the prithe voltage of
is
, the potenmary voltage of the transformer,
tial voltage of point reduces to zero. So
conducts,
at
, and the voltage of
is clamped
clamping
accordingly.
at 2
[Refer to Fig. 3(g)]
7) Stage 7
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CHEN et al.: NOVEL ZVS PWM FULL BRIDGE CONVERTER
Fig. 3. Equivalent circuits of each operation stages. (a)
795
. (b)
. (c)
. (d)
. (e)
. (f)
. (g)
. (h)
.
The reset winding is in series with the primary winding
turns off, the further simplified equivalent circuit
after
of this stage is shown in Fig. 4(b). During this stage,
resonates with
. The rectifier voltage
is given
by
Fig. 4. Further equivalent circuits. (a) Stage 7. (b) Stage 8.
(1)
declines downwards to the reflected filter inductance
current when
conducts, and increases in the negative
,
direction. The voltage of the reset winding is
decrease quickly.
which is applied to , making
is greater than
before , and the current difference
flows through . This stage finishes when equals
at
, and
turns off naturally. The further simplified equivalent circuit of this stage is shown in Fig. 4(a).
[Refer to Fig. 3(h)]
8) Stage 8
where
, and
.
Equation (1) illustrates that the maximum value of
will never exceed
though slight oscillation exists. In practice,
will finally stay at the average value
since the inherent parasitic resistance
exists in the power circuit, which will be presented in Section IV.
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796
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008
A resistor or two back-to-back Zener diodes are introduced
to reduce the current in the clamping diodes [16], however, these components are lossy. In the proposed converter, there is no component is added and the method is
lossless.
III. COMPARISON BETWEEN THE CONVERTERS
WITH/WITHOUT RESET WINDING
A. Conduction Loss
It can be known from the above analysis that the voltage oscillation across the rectifier diodes can be eliminated in both the
full-bridge converters with and without reset winding, the difference is the conduction time of the clamping diode.
Before the reset winding is introduced, when the clamping
diode conducts, the resonant inductance is shorted and its
current keeps constant, the difference between the resonant
inductance current and the primary current flows through the
clamping diode. The conduction time of the clamping diode
depends on the rise rate of the filter inductance current. The
filter inductance is usually quite large, so the conduction time
of the clamping diode is very long.
When the reset winding is introduced, a negative voltage
is applied to the resonant inductance, makes its current
decays rapidly, so the clamping diode current declines to zero
rapidly correspondingly and its average value is also reduced,
and the efficiency can be further increased.
Fig. 5. Primary current comparison. (a) Without reset winding. (b) With reset
winding.
For the convenience of description, we define the turns ratio
of the transformer as
(6)
B. Transformer Turns Ratio
The output voltage , which is the average value of
,
can be calculated according to Fig. 2(b). The time intervals
and
are very short to be neglected compared with
, so
is given by
(2)
where
is the switching period.
is shorter than
by choosing the proper turns
Generally,
ratio of the reset winding to the primary winding, then (2) becomes
C. Output Filter Inductance and Clamping Diode Current
The transformer primary current and resonant current waveforms with and without reset winding are shown in Fig. 5.
is the primary current spike caused by the resonance of the resonant inductance and the junction capacitor of the rectifier diode
(7)
The rise slope of the output filter inductance current is
(3)
(8)
is the secondary duty cycle.
where
The output/input voltage ratio of the full-bridge converter
without the reset winding is
Taking into account the voltage drops on the clamping diode
and the switch, the decay slope of the resonant inductance when
the clamping diode conducts is
(4)
(9)
where
is the primary turns of the transformer.
From (3) and (4), we can see that in order to obtain the same
voltage ratio, we should have
(5)
where
is the output load current;
is the static
is the
drain-to-source on-resistance of the main switch; and
forward voltage drop of the clamping diode.
From (8) and (9), the conduction time of the clamping diode
without reset winding can be derived as
It means the transformer primary winding in the full-bridge
converter is split into two windings, and one of them is used as
the reset winding in the proposed converter.
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(10)
CHEN et al.: NOVEL ZVS PWM FULL BRIDGE CONVERTER
Fig. 6. Maximum value of
797
when reset winding is not introduced.
Fig. 7. Clamping diode conduction time comparison (
V).
In order to avoid reverse recovery of the clamping diode,
should be smaller than
. Substitution of (4) into (10),
yields
(11)
In the proposed converter, when the clamping diode conducts,
the decay slope of the resonant inductance current (the voltage
drops on the clamping diode and the switch are so small compared with the reset winding voltage that they are neglected) is
(12)
The conduction time of the clamping diode can be derived
from (8) and (12)
(13)
should be shorter than
to avoid
Similarly,
reverse recovery of the clamping diode. Substitution of (3) into
Fig. 8. Transformer winding structures. (a) Turns ratio
. (b) Turns ratio
. (c) Turns ratio: 15:13.
(13), yields
(14)
In order to observe the concrete comparisons, a prototype is
designed and built with the following parameters:
% VDC;
• input voltage
: 180 VDC;
• output voltage
• maximum output current : 6 A;
• switching frequency : 100 kHz;
H (Ferroxcube, core:
• resonant inductance
E32/16/9-3C90, bobbin: CPH-E 42/20-1S -12PD, 8 turns
Litz wire: dia. 0.1 mm, 200 strands);
: IRFP450 (International Recti• main switches
;
fier), and its
• clamping diodes: DSEI30-06A (IXYS), and its forward
V;
voltage
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798
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 2, MARCH 2008
Fig. 9. Waveforms of the Tr_lag type converters. (a) Without reset winding. (b) With reset winding
.
• rectifier diodes (full-bridge rectifier): DSEI30-06A
(IXYS);
: designed with two cases: 14:1:13, 13:2:13,
•
respectively;
• turns ratio : 15:13;
: 600 F, which is approximately
• reflected capacitor
calculated by the experimental results.
According to (11), Fig. 6 shows the maximum filter inductance to ensure the clamping diode turn off naturally, it can be
should be less than 230 H.
seen that
The minimum duty cycle of the proposed converter is
(15)
So the minimum conduction time
is
(16)
. (c) With reset winding
is assumed to be large enough to be infinity, hence the
is
maximum value of
(17)
When
It can be seen that the maximum
is shorter than the min, so the clamping diodes
imum conduction time
can be turned off naturally without reverse recovery over the
whole input voltage range.
Fig. 7 shows the conduction time of the clamping diodes of
the converters with and without reset winding, where the output
filter inductance varying from 100 to 200 H. It can be seen that
the conduction time of the clamping diode is reduced significantly in the proposed converter and insusceptible to the output
filter inductance. So the output filter inductance can be designed
to be large to obtain small current ripple and thus the filter capacitance is reduced.
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CHEN et al.: NOVEL ZVS PWM FULL BRIDGE CONVERTER
799
Fig. 10. Waveforms of the leading switch and the lagging switch. (a)
and
of the leading switch
. (b)
and
of the lagging switch
.
The voltage stress of the rectifier diode in the proposed con, which is slightly higher than the converter
verter is 2
without reset winding, and the difference is
(18)
In the prototype, however, the difference is too small to influence the choice of the rectifier diodes.
IV. EXPERIMENTAL VERIFICATION
A prototype with 180V/6A output of the proposed ZVS
PWM full-bridge converter was built and tested to verify the
operation principle. The output filter inductance is 230 H
(Ferroxcube, core: E42/21/20-3C90, bobbin: CPH-E 42/20-1S
-12PD, 40 turns, copper strip and its cross section size is
Fig. 11. Waveforms of the
(b) With reset winding
type converters. (a) Without reset winding.
. (c) With reset winding
.
0.1 mm 20 mm) and the other parameters are the same as
listed in Section III.
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type converter is also higher
ductance. The efficiency of
type converter.
than that of
V. CONCLUSION
Fig. 12. Efficiency comparison of three kinds of converter.
Three kinds of transformer are built with different turns ratio,
and their winding structures are shown in Fig. 8. All the transformers are built with the same core, bobbin and the size of the
winding (Ferroxcube, core: E42/21/20-3C90, bobbin: CPH-E
42/20-1S -12PD, primary and second windings: copper strip and
its cross section size is 0.1 mm 25 mm). It can be seen that the
winding structures of three transformers are the same, and the
only difference is the primary winding is split into two windings and a connecting port is added in the proposed converter.
Hence, there is almost no extra cost and labor compared with
traditional transformer [Fig. 8(c)].
and
Fig. 9 shows the waveforms of
(from the top to the bottom) at full load under the nominal
input voltage 270 V. Fig. 9(a) shows the waveforms of the
converter without reset winding [17]. Fig. 9(b) and 9(c) show
type converter [see
the waveforms of the proposed
and
Fig. 1(a)] with turns ration
14:1:13, respectively. It can be seen that the clamping diode
conduction time is shortened when the reset winding is added,
is, the shorter conduction time is. As the
and the larger
conduction time is shortened, the clamping diode current is
reduced, leading to a low conduction loss. The waveform of
has slight oscillation after the clamping diodes turn off,
however, the maximum value never exceed
.
Fig. 10(a) and (b) show the waveforms of the gate-source
, the drain-source voltage
and the drain current
voltage
of
and
, respectively. It can be seen that all switches
realize ZVS.
type converters [include the conThe waveforms of
full-bridge converter and the proposed
ventional
type, Fig. 1(b)] are shown in Fig. 11. It can be seen that the
clamping diodes conduct twice in a switching period comparing
type converters and the other waveforms
with that of the
are almost the some.
Fig. 12 shows the conversion efficiency curves comparison at
full load. It can be seen that the efficiency of the proposed ZVS
PWM full bridge converter is higher than that of the converter
without reset winding due to the reduced conduction losses of
the clamping diodes, the leading switches and the resonant in-
A new ZVS PWM full-bridge converter is proposed in this
paper, it employs an additional reset winding to make the
clamping diode current decay rapidly when the clamping diode
conducts, thus the conduction losses of the clamping diodes, the
leading switches and the resonant inductance are reduced and
the conversion efficiency can be increased. In the meanwhile,
the clamping diodes can be turned off naturally without reverse
recovery over the whole input voltage range, and the output
filter inductance can be designed to be large to obtain small
current ripple, leading to reduced filter capacitance. Compared
with the traditional full bridge converter [14]–[16], the proposed circuit provides another simple and effective approach
to avoid the reverse recovery of the clamping diodes. The operation principle, features and comparisons are illustrated. The
Experimental results from the prototype are shown to verify the
feasibility of the proposed converter.
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CHEN et al.: NOVEL ZVS PWM FULL BRIDGE CONVERTER
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Xinbo Ruan (M’97–SM’01) was born in Hubei,
China, in 1970. He received the B.S. and Ph.D.
degrees in electrical engineering from Nanjing University of Aeronautics and Astronautics (NUAA),
Nanjing, China, in 1991 and 1996, respectively.
In 1996, he joined the faculty of the College of
Automation Engineering, NUAA where he is now a
Professor. He has authored over 100 technical papers in journals and conferences and also published
three books. His main research interests include softswitching dc–dc converters, soft-switching inverters,
power factor correction converters, modeling the converters, power electronics
system integration and renewable energy generation system.
Dr. Ruan received the honor of “Delta Scholar” in 2003. He is a Member of
the IEEE Power Electronics Society.
Wu Chen (S’05) was born in Jiangsu, China, in
1981. He received the B.S. and M.S. degrees in
electrical engineering from Nanjing University of
Aeronautics and Astronautics (NUAA), Nanjing,
China, in 2003 and 2006, respectively, where he
is currently pursuing the Ph.D. degree in electrical
engineering.
His main research interests are soft-switching
dc–dc converters and power electronics system
integration.
Rongrong Zhang was born in Jiangsu, China, in
1983. She received the B.S. degree in electrical
engineering from Nanjing University of Aeronautics
and Astronautics (NUAA), Nanjing, China, in 2005,
where she is currently pursuing the M. S. degree in
electrical engineering.
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