power electronics chapter 8 soft-switching techniques
TRANSCRIPT
Power ElectronicsPower Electronics
Chapter 8
Soft-Switching Techniques
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Pursuing of higher switching frequencyPursuing of higher switching frequency
Benefits
Better waveform• PWM waveform will be closer to expected waveform• Harmonics is easier to be filtered
Faster response
Smaller volume and weight• 4.44fNfNAB
• LC
f2
1
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Disadvantages of higher switching frequencyDisadvantages of higher switching frequency
DisadvantagesDisadvantages
Higher power losses on power semiconductor devicesHigher power losses on power semiconductor devices– Power loss=f x Energy loss at each switchingPower loss=f x Energy loss at each switching
More severe electromagnetic interference (EMI)More severe electromagnetic interference (EMI)– Steeper edges introduce more noisesSteeper edges introduce more noises
– Easier to be radiatedEasier to be radiated
SolutionSolution
Soft-switching techniquesSoft-switching techniques
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OutlineOutline
8.1 Basic concepts on soft-switching8.1 Basic concepts on soft-switching
8.2 Classification of soft-switching techniques8.2 Classification of soft-switching techniques
8.3 Typical soft-switching circuits and techniques8.3 Typical soft-switching circuits and techniques
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8.1 Basic concepts on soft-switching8.1 Basic concepts on soft-switching
t
ui
u i
t
ui
ui
t
p
t
p
O
O
O
O
Hard-switchingHard-switching
a) Turning-on b) Turning-off
The process of power semiconductor device The process of power semiconductor device hard-switchinghard-switching
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The concept of soft-switchingThe concept of soft-switching
Soft-switchingSoft-switching
a) Turning-on b) Turning-off
The process of power semiconductor device The process of power semiconductor device
soft-switchingsoft-switching
t
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u i
t
ui
ui
t
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t
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Two types of soft-switchingTwo types of soft-switching
ZVS—Zero-voltage switchingZVS—Zero-voltage switching
Specifically means zero-voltage turn-on, i.e., the Specifically means zero-voltage turn-on, i.e., the
voltage across the device is reduced to zero before the voltage across the device is reduced to zero before the
current increasescurrent increases
ZCS—Zero-current switchingZCS—Zero-current switching
Specifically means zero-current turn-off, i.e., the Specifically means zero-current turn-off, i.e., the
current flowing through the device is reduced to zero current flowing through the device is reduced to zero
before the voltage increasesbefore the voltage increases
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8.2 Classification of soft-switching 8.2 Classification of soft-switching techniquestechniques
Quasi-resonant soft-switchingQuasi-resonant soft-switching
ZVS PWM (zero-voltage-switching PWM) and ZCS ZVS PWM (zero-voltage-switching PWM) and ZCS
PWM (zero-current-switching PWM)PWM (zero-current-switching PWM)
ZVT PWM (zero-voltage-transition PWM) and ZCT ZVT PWM (zero-voltage-transition PWM) and ZCT
PWM (zero-current-transition PWM)PWM (zero-current-transition PWM)
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The concept of basic switch cellThe concept of basic switch cell
VD
S L
a)
L
S
VD
LS VD
c) d)
VD
S L
b)
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Quasi-Resonant Converter—QRCQuasi-Resonant Converter—QRC
ZVS QRCZVS QRCZCS QRCZCS QRCZVS MRC (multi-resonant converter)ZVS MRC (multi-resonant converter)Resonant DC link converterResonant DC link converter
S
V D
L r L
C r
SV D
L r L
C r1
C r2
S
L r
C r
V D
L
a ) Z V S Q R C b ) Z C S Q R C c ) Z V S M R C
Basic switching cells for QRC
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ZVS PWM converter and ZCS PWM converterZVS PWM converter and ZCS PWM converter
Feature: use of auxiliary switchFeature: use of auxiliary switch
S L r
C r
VD
LS 1
S
VD
L r L
C r
S 1
a) b)
Basic switching cells for a) ZVS PWM and b) ZCS PWM
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ZVT PWM converter and ZCT PWM converterZVT PWM converter and ZCT PWM converter
Feature: auxiliary switch is in parallel with main switchFeature: auxiliary switch is in parallel with main switch
S
L r
VD
LS 1
C r
VD 1
L r C r S 1
S
VDVD 1
L
a) b)
Basic switching cells for a) ZVT PWM and b) ZCT PWM
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8.3 Typical soft-switching circuits 8.3 Typical soft-switching circuits and techniques and techniques
ZVS QRCZVS QRC
Resonant DC link converterResonant DC link converter
Phase-shift full bridge ZVS PWM converterPhase-shift full bridge ZVS PWM converter
ZVT PWM converterZVT PWM converter
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ZVS QRCZVS QRC
ttoo ~ ~ tt1 1 tt11 ~ ~ tt22
U i
C r
S
VD S
L r
VD
L
C
A
R
S
uS (uCr)
iS
iLr
uVD
t0t1 t2 t3t4 t6 t0
t
t
t
t
t
t5O
O
O
O
O
C r
U i
+u Cr I L
A C r
U i
+u Cr i L r
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Resonant DC link converterResonant DC link converter
CircuitCircuit
Equivalent circuit to RDCLEquivalent circuit to RDCL
L r
U iS
C r
VD
S
L r
U iS
C r
VD S
L
iL r
+u C r
I L
Rt0 t1 t2 t3 t4 t0
iL r
u C r
U i
IL
t
tO
O
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Summary of QRCSummary of QRC
DisadvantagesDisadvantages
– Voltage stress increased due to the resonant peakVoltage stress increased due to the resonant peak
– Current RMS value increased due to large Current RMS value increased due to large
circulating energycirculating energy
– Variable switching frequency due to pulse-frequency Variable switching frequency due to pulse-frequency
modulation (PFM) controlmodulation (PFM) control
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Phase-shift full-bridge ZVS PWM converterPhase-shift full-bridge ZVS PWM converter
CircuitCircuit
S 1
S 2
S 3
S 4
C S1
C S4C S2
C S3
VD 2
VD 1
L r
LA
BU i
u R
C R
+
-
S 1
S 3
S 4
S 2
uA B
u L r
iL r
u T 1
u R
iV D 1
iV D 2
iL
t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t0t9t8 t
t
t
t
t
t
t
t
t
t
t
t
O
O
O
O
O
O
O
O
O
O
O
O
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Phase-shift full-bridge ZVS PWM converterPhase-shift full-bridge ZVS PWM converter
Equivalent circuit during Equivalent circuit during
tt11 ~ ~ tt22
Equivalent circuit during Equivalent circuit during
tt33 ~ ~ tt44
iL r
iL
k T :1C S1
S 4
L r
LVD 1
U i
U o
+
C S2 VD S2
AR
iL r
iL
C S3
S 2
L r
LVD 1
U i
U o
+
C S4
VD S3
VD 2
B R
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Summary of ZVS or ZCS PWM converterSummary of ZVS or ZCS PWM converter
Improvement over QRCImprovement over QRC
– Voltage and current are basically square-wave, Voltage and current are basically square-wave,
therefore stresses are greatly reducedtherefore stresses are greatly reduced
– Constant switching frequency due to pulse-width Constant switching frequency due to pulse-width
modulation (PWM) control modulation (PWM) control
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ZVT PWM converterZVT PWM converter
CircuitCircuit
L
S C r
S 1
L r
VD 1
VD
CU i
+
U o
I L
iL r
iVD
VD S
R
Equivalent circuit during t1 ~ t2
S
S 1
u S
iL r
iS 1
u S 1
iD
iS
IL
t0 t1 t2 t3 t4 t5
t
t
t
t
t
t
t
t
O
O
O
O
O
O
O
O
L
S 1
L riL r
U i
I L
C rVD S
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Summary of ZVT or ZCT PWM converterSummary of ZVT or ZCT PWM converter
Improvement over ZVS or ZCS PWM converterImprovement over ZVS or ZCS PWM converter
– Soft-switching can be achieved in a wider range of Soft-switching can be achieved in a wider range of
input voltage and load currentinput voltage and load current
– Circulating energy is reduced to minimum so that Circulating energy is reduced to minimum so that
efficiency is increasedefficiency is increased