Soft‐Switching PWM Full‐Bridge Converters
Presented by
Xinbo Ruan
Aero‐Power Sci‐tech Center
Nanjing University of Aeronautics and Astronautics
2012-12-6
1
Outlines
• Backgrounds
• PWM Strategies for Soft‐Switching Full‐Bridge
Converters
• ZVS PWM Full‐Bridge Converters
• ZVZCS PWM Full‐Bridge Converters
• Conclusion
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2
Outlines
• Backgrounds
• PWM Strategies for Soft‐Switching Full‐Bridge
Converters
• ZVS PWM Full‐Bridge Converters
• ZVZCS PWM Full‐Bridge Converters
• Conclusion
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3
Buck-Derived Converters
Single-switch forward
Q1
D1
DR
RLd
Tr
*
Vin
+
*
DFW
D2
Lf
Q2
Half-bridge
Cf
Vo
_
Dual-switch forward
Q1
A
D1
Q2
Q3
D3
Q4
B
D2
Vin
DR1
Tr
*
*
D4
C
Lf
RLd
+
Vo
_
Cf
*
D
Push-pull
Full-bridge
DR2
Among
the buck-derived converters, the full-bridge converter can output maximum 4
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power, given that the power switches have the same voltage and current ratings.
Applications of Full-Bridge Converters
The full-bridge converter have widely used
in medium-to-high power dc-dc conversions:
Q1
A
D1
Q2
Q3
D3
Q4
B
D2
Switching-mode rectifier for
telecommunications, power system, etc.;
Vin
DR1
Tr
*
*
D4
C
electroplating power supply;
Lf
RLd
+
Vo
_
Cf
*
D
DR2
dc-dc converters for electrical-powered
vehicles.
dc-dc converters for aircraft, ship and
satellites.
…
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5
Objectives of This Presentation
Q1
A
D1
Q2
Q3
D3
Q4
B
Soft-switching techniques
D2
Vin
DR1
Tr
*
*
D4
C
Lf
RLd
Various
topologies
+
Vo
_
Cf
*
Various control
strategies
D
DR2
Reveal the relationship among the existing modulation strategies
Reveal the relationship among the existing topologies
Propose other modulation strategies and topologies
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6
Outlines
• Backgrounds
• PWM Strategies for Soft‐Switching Full‐Bridge
Converters
• ZVS PWM Full‐Bridge Converters
• ZVZCS PWM Full‐Bridge Converters
• Conclusion
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7
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8
Basic Operating Principle of Full-Bridge Converter
Q1
A
D1
Q2
Q3
D3
Q4
B
D2
Vin
DR1
Tr
*
*
D4
C
Lf
RLd
+
Vo
_
Cf
*
D
DR2
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9
PWM Strategies for Full-Bridge Converter
Q1
A
D1
Q2
Q3
D3
Q4
B
D2
Vin
DR1
Tr
*
*
D4
C
Lf
RLd
+
Vo
_
Cf
*
D
DR2
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10
A Family of PWM Strategies for FB Converter
Basic
PWM
This strategy
has been
successfully
used in a
power supply
One leg
operates in
complementary
with 50% duty
cycle
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PhaseShifted
Control
11
Categorization of the PWM Strategies
According to the turn-off sequence of the
diagonal switches, the family of PWM
strategies can be divided into two categories:
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1.
the diagonal switches turn off
simultaneously;
2.
the turn-off instances of the diagonal
switches are staggered. One turns off
before the other.
12
The Diagonal Switches Turn Off Simultaneously
vAB
Vin
0
t
Vin
ip
0
t
t0 t1 t2 t3
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t4
13
The Diagonal Switches Turn Off Simultaneously
Q1 和 Q4 是
零电压关断
vAB
Vin
0
t
Vin
ip
0
t
t0 t1 t2 t3
t4
vA>vB
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The Diagonal Switches Turn Off Simultaneously
Q1 和 Q4 是
零电压关断
vAB
Vin
0
t
Vin
ip
0
t
t0 t1 t2 t3
t4
vA>vB
both the two rectifier diode conduct
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The Diagonal Switches Turn Off Simultaneously
Q1 和 Q4 是
零电压关断
vAB
Vin
0
t
Vin
ip
0
t
t0 t1 t2 t3
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t4
16
The Diagonal Switches Turn Off Simultaneously
Q1 和 Q4 是
零电压关断
vAB
Vin
0
t
Vin
Q1 和 Q4 是
硬开通
Q2 和 Q3 是
硬开通
ip
0
t
t0 t1 t2 t3
t4
If the diagonal switches turn off simultaneously, the power
switches CAN NOT realize soft-switching.
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17
Turn-Off Instances of Diagonal Switches Staggered
If the turn-off instances of the diagonal
switches is staggered, the switching
transition will be improved.
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1.
the switches turning off firstly
constitute the LEADING LEG;
2.
the switches turning off lately
constitute the LAGGING LEG.
18
Soft-Switching for the Leading Leg
C1 充电
When the leading switch turns off, the
current flowing out/into point A is the
reflected output filter inductor current, a
nearly constant current source.
C3 放电
the leading leg CAN ONLY realize
zero-voltage-switching (ZVS), and
CANNOT realize zero-currentswitching (ZCS);
☺ the leading leg is easier to realize ZVS.
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19
Zero State
Zero state
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Constant current mode: ip keep
nearly constant
Lagging leg realize ZVS
Current reset mode: ip decays
to zero
Lagging leg realize ZCS
20
The Lagging Leg Realizes ZVS
C2放电
C4充电
the lagging switches should have
capacitors in parallel with them, so that
they can realize ZVS;
ONLY the leakage inductor provides
energy for achieving ZVS for the
lagging leg, so the lagging leg is
difficult to realize ZVS than the
leading leg.
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The Lagging Leg Realizes ZCS
the lagging switches can realize ZCS if
zero state operating in current reset
mode.;
The lagging switches should have No
capacitor in parallel with them.
At zero state, when the primary current
ip decays to zero, it should keep at zero.
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Soft-Switching Types of PWM FB Converter
Soft-switching PWM full-bridge converter
ZVS type
Both the leading leg and lagging
leg realize ZVS.
ZVZCS type
The leading leg realizes ZVS,
while the lagging leg realizes ZCS.
The realization of soft-switching for the power switches
DOES NOT require any auxiliary power switch,
it utilizes appropriate switching mechanism of the
four power switches.
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ZVS Type: The Switching of Lagging Switches
ip
t
0
Q1
t
Q3
t
Q4
t
Q2
t
0
t0 tx Ts/2
In order to ensure ZVS for the lagging switches, the turn-off time instant of
the lagging switches should be delayed to Ts/2, i.e., the conducting time of the
lagging switches should be Ts/2.
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ZVS Type: The Switching of Leading Switches
ip
t
0
Q1
t
Q3
t
Q4
t
Q2
t
0
t0 tx Ts/2
Since ip flowing through the anti-paralleled diode of Q3 at zero state, the turnon instant can be at any time, so the conduction time of the leading switches
can be three kinds.
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ZVS Type: PWM Strategies
Phase-Shifted Control
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26
ZVZCS Type: The Switching of Leading Switches
In order to ensure zero-voltage turn-on of the leading switches, the turn-on
time instant should be moved forward and let the conducting time to be Ts/2.
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27
ZVZCS Type: The Switching of Lagging Switches
In order to ensure zero-current turn-off of the lagging switches, the turn-off
time instant should be delayed to the time when ip is reset or even to let the
conducting time to be Ts/2.
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28
ZVZCS Type: PWM Strategies
Phase-Shifted Control
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29
Outlines
• Backgrounds
• PWM Strategies for Soft‐Switching Full‐Bridge
Converters
• ZVS PWM Full‐Bridge Converters
• ZVZCS PWM Full‐Bridge Converters
• Conclusion
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30
Basic ZVS PWM Full-Bridge Converter
Advantages
Q1
A
D1
Q2
C1
D2
☺ The junction capacitors of the power
switches and the leakage inductor of
the transformer are fully used to
achieve ZVS for the power switches.
C2
B
Vin
Q3
D 3 C3
ip
Llk
Tr
Q4
DR1
C
+
vrect
_
*
* *
Lf
RLd
+
Vo
_
Cf
D
DR2
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D4 C4
☺ No auxiliary power switches and
element is required. This leads to
simple topology.
☺ It operates with constant frequency,
leading to easy optimization of the
transformer and input and output filter.
☺ Various commercial controller IC are
available, leading to simple
implementation of control circuit.
31
Basic ZVS PWM Full-Bridge Converter
Characteristics
Q1
A
D1
Q2
C1
D2
☺ The leading leg can realize ZVS in a
wide load range because both the
energy stored in the filter inductor and
leakage inductor are utilized.
C2
B
Vin
Q3
D 3 C3
ip
Llk
Tr
Q4
DR1
C
+
vrect
_
*
* *
Lf
RLd
+
Vo
_
Cf
D
DR2
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D4 C4
The lagging leg is relatively difficult to
realize ZVS since only the energy
stored in the leakage inductor is used.
The leakage inductor or external
resonant inductor results in duty cycle
loss, thus the primary-to-secondary
turns ratio of the transformer should be
reduced, which leading to high voltage
stress of the rectifier diodes and
primary current stress..
32
Increase Load-Range of ZVS for Lagging Switches
The auxiliary inductor
current is independent
with the load current
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Increase Load-Range of ZVS for Lagging Switches
The auxiliary inductor current increases with the load current
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34
Increase Load-Range of ZVS for Lagging Switches
Ca1
C
Ta
ia1
La iLa
_ vLa
+
D
Ca2
*
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The auxiliary inductor current is adaptive with the load current,
i.e., it is reduced as the load current increases.
35
Outlines
• Backgrounds
• PWM Strategies for Soft‐Switching Full‐Bridge
Converters
• ZVS PWM Full‐Bridge Converters
• ZVZCS PWM Full‐Bridge Converters
• Conclusion
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36
Block Voltage Source for Resetting Primary Current
Q1
Vin
D1
Q2
C1
Llk
D2
ip
B
A
Q3
Q4
D3 C3
D4
Q1
Vin
C1
A
Q3
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D1
D 3 C3
Llk
vanti
_
Q2
ip
D2
B
+
Q4
D4
37
Implementation of Block Voltage Source
When ip > 0,
the polarity of
Cb is positive
When ip < 0,
the polarity of
Cb is negative.
ip
0
t
vcb
0
t
Q1
t
Q3
t
Q4
t
Q2
t
0
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t0 t1 t2
t3 t4 t5
t6
38
Blocking Reverse Flowing Path of ip at Zero State
Possible places to block the reverse
flowing path of ip
AC/AO segment;
AB segment;
BC/BO segment.
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Blocking Reverse Flowing Path of ip at Zero State
Q1
A
D1
C1
Q2
Cb
Q3
B
Ls
Vin
D3 C3
ip
Tr
DR1
C
+
vrect
_
*
* *
A
D1
Q2
C1
D2
B
Vin
Q4
Llk
Q1
D2
Q3
D4
Lf
RLd
+
Vo
_
Cf
D
Q4
Llk
D3 C3
ip
Tr
DR1
Cf
RLd
+
Vo
_
DR2
Db1
DR2
Lf
+
vrect
_
*
* *
D4
*
Da3
Cb
*
Db2
AB segment to block the reverse flowing path of ip
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Blocking Reverse Flowing Path of ip at Zero State
Q1
A
D1
Q2
C1
D2
B
Vin
Q3
Q4
Llk
D3 C3
ip
Tr
DR1
Lf
+
vrect
_
*
* *
D4
DR2
RLd
+
Cb1
Db2
Db3
Db1
Cf
Vo
Cb2
_
AB segment to block the reverse flowing path of ip
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Blocking Reverse Flowing Path of ip at Zero State
D2
Q1
A
D1
C1
Q2
Cb
Vin
Q3
Q4
D4
Llk
D3 C3
ip
Tr
B
DR1
C
+
vrect
_
*
* *
Lf
RLd
+
Vo
_
Cf
D
DR2
BC/BO segment to block the reverse flowing path of ip
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Outlines
• Backgrounds
• PWM Strategies for Soft‐Switching Full‐Bridge
Converters
• ZVS PWM Full‐Bridge Converters
• ZVZCS PWM Full‐Bridge Converters
• Conclusion
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Conclusion
A family of PWM strategies are proposed for full-bridge converter, which can
be divided into two categories: one is that the diagonal switches turn off
simultaneously, and the other is that the diagonal switches turn off at different
time instance. The form one cannot achieve soft-switching for the power
switches, and the latter one provides the possibility of achieve soft-switching,
thus the concept of LEADING LEG and LAGGING LEG is introduced.
The leading leg CAN ONLY and is EASY to realize ZVS, and the lagging
leg can realize ZVS or ZCS, thus the soft-switching PWM full-bridge
converter can be categorized into two kinds: One is ZVS type, for which both
the leading leg and lagging leg realize ZVS; and the other one is ZVZCS type,
for which the leading leg realize ZVS, and the lagging leg realize ZCS. The
suitable PWM strategies for ZVS type and ZVZCS type full-bridge converter
are pointed out.
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Conclusion
For ZVS PWM full-bridge converter, the leading leg is easier to realize ZVS
than the lagging leg. Some auxiliary circuits to help the lagging leg to realize
ZVS are presented.
For ZVZCS PWM full-bridge converter, the method of resetting the primary
current at zero state are proposed, and the relationship of the several existing
topologies are revealed. Furthermore, a new topology is proposed.
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Thanks for your attention !
Questions? / Answer!
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