γλώσσες
Σελίδες
Νομικός
Power ElectronicsPower Electronics
Chapter 7
Soft-Switching Techniques
Pow
erE
l ect
roni
cs
2
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• 4.44fNφ =4.44fNAB
•LC
fπ2
1=
Pow
erE
l ect
roni
cs
3
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
SoftSoft--switching techniquesswitching techniques
Pow
erE
l ect
roni
cs
4
OutlineOutline7.1 7.1 Basic concepts on softBasic concepts on soft--switchingswitching
7.2 Classification of soft7.2 Classification of soft--switching techniquesswitching techniques
7.3 Typical soft7.3 Typical soft--switching circuits and techniquesswitching circuits and techniques
Pow
erE
l ect
roni
cs
5
7.1 7.1 Basic concepts on softBasic concepts on soft--switchingswitching
t
u
iu i
t
u
i
ui
t
p
t
p
O
O
O
O
HardHard--switchingswitching
a) Turning-on b) Turning-off
The process of power semiconductor device The process of power semiconductor device hardhard--switchingswitching
Pow
erE
l ect
roni
cs
6
The concept of softThe concept of soft--switchingswitching
SoftSoft--switchingswitching
a) Turning-on b) Turning-off
The process of power semiconductor device The process of power semiconductor device softsoft--switchingswitching
t
u
i
u i
t
u
i
ui
t
p
t
p
O
O
O
O
Pow
erE
l ect
roni
cs
7
Two types of softTwo types of soft--switchingswitching
ZVSZVS——ZeroZero--voltage switchingvoltage switchingSpecifically means zeroSpecifically means zero--voltage turnvoltage turn--on, i.e., the 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
ZCSZCS——ZeroZero--current switchingcurrent switchingSpecifically means zeroSpecifically means zero--current turncurrent turn--off, i.e., the 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
Pow
erE
l ect
roni
cs
8
7.2 Classification of soft7.2 Classification of soft--switching switching techniquestechniques
QuasiQuasi--resonant softresonant soft--switchingswitching
ZVS PWM (zeroZVS PWM (zero--voltagevoltage--switching PWM) and ZCS switching PWM) and ZCS PWM (zeroPWM (zero--currentcurrent--switching PWM)switching PWM)
ZVT PWM (zeroZVT PWM (zero--voltagevoltage--transition PWM) and ZCT transition PWM) and ZCT PWM (zeroPWM (zero--currentcurrent--transition PWM)transition PWM)
Pow
erE
l ect
roni
cs
9
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)
Pow
erE
l ect
roni
cs
10
QuasiQuasi--Resonant ConverterResonant Converter——QRCQRCZVS QRCZVS QRCZCS QRCZCS QRCZVS MRC (multiZVS MRC (multi--resonant converter)resonant converter)Resonant DC link converterResonant DC link converter
S
VD
Lr L
Cr
SVD
Lr LCr1
Cr2
S
Lr
Cr
VD
L
a) ZVS QRC b) ZCS QRC c) ZVS MRC
Basic switching cells for QRC
Pow
erE
l ect
roni
cs
11
ZVS PWM converter and ZCS PWM converterZVS PWM converter and ZCS PWM converterFeature: use of auxiliary switchFeature: use of auxiliary switch
S Lr
Cr
VD
LS1
S
VD
Lr L
Cr
S1
a) b)
Basic switching cells for a) ZVS PWM and b) ZCS PWM
Pow
erE
l ect
roni
cs
12
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
Lr
VD
LS1Cr
VD1
Lr Cr S1
SVDVD1
L
a) b)
Basic switching cells for a) ZVT PWM and b) ZCT PWM
Pow
erE
l ect
roni
cs
13
7.3 Typical soft7.3 Typical soft--switching circuits switching circuits and techniquesand techniques
ZVS QRCZVS QRC
Resonant DC link converterResonant DC link converter
PhasePhase--shift full bridge ZVS PWM convertershift full bridge ZVS PWM converter
ZVT PWM converterZVT PWM converter
Pow
erE
l ect
roni
cs
14
ZVS QRCZVS QRC
ttoo ~ ~ tt1 1 tt11 ~ ~ tt22
Ui
Cr
S
VDS
Lr
VD
L
C
A
R
S
uS (uCr)
iS
iLr
uVD
t0t1 t2 t3t4 t6 t0
t
t
t
t
tt5
O
O
O
O
O
Cr
Ui
+ uCr IL
A Cr
Ui
+ uCr iLr
Pow
erE
l ect
roni
cs
15
Resonant DC link converterResonant DC link converterCircuitCircuit
Equivalent circuit to RDCLEquivalent circuit to RDCL
Lr
UiS
CrV
DS
Lr
Ui SCr
VDS
L
iLr
+uCr
IL
R t0 t1 t2 t3 t4 t0
iLr
uCr
Ui
IL
t
tO
O
Pow
erE
l ect
roni
cs
16
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 pulseVariable switching frequency due to pulse--frequency frequency modulation (PFM) controlmodulation (PFM) control
Pow
erE
l ect
roni
cs
17
PhasePhase--shift fullshift full--bridge ZVS PWM converterbridge ZVS PWM converter
CircuitCircuit
S1
S2
S3
S4
CS1
CS4CS2
CS3
VD2
VD1
Lr
LA
BUi
uR
C R
+
-
S1
S3
S4
S2
uAB
uLr
iLr
uT1
uR
iVD1
iVD2
iL
t0 t1 t2 t3t4 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
Pow
erE
l ect
roni
cs
18
PhasePhase--shift fullshift full--bridge ZVS PWM converterbridge ZVS PWM converter
Equivalent circuit during Equivalent circuit during tt11 ~ ~ tt22
Equivalent circuit during Equivalent circuit during tt33 ~ ~ tt44
iLr
iLkT:1CS1
S4
Lr
LVD1
Ui
Uo
+
CS2 VDS2
AR
iLr
iL
CS3
S2
Lr
LVD1
Ui
Uo
+
CS4
VDS3
VD2
B R
Pow
erE
l ect
roni
cs
19
Summary of ZVS or ZCS PWM converterSummary of ZVS or ZCS PWM converter
Improvement over QRCImprovement over QRC–– Voltage and current are basically squareVoltage and current are basically square--wave, wave,
therefore stresses are greatly reducedtherefore stresses are greatly reduced
–– Constant switching frequency due to pulseConstant switching frequency due to pulse--width width modulation (PWM) control modulation (PWM) control
Pow
erE
l ect
roni
cs
20
ZVT PWM converterZVT PWM converter
CircuitCircuit
L
S Cr
S1
Lr
VD1
VD
CUi
+
Uo
IL
iLr
iVD
VDSR
Equivalent circuit during t1 ~ t2
S
S1
uS
iLr
iS1
uS1
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
S1
LriLr
Ui
IL
CrVDS
Pow
erE
l ect
roni
cs
21
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–– SoftSoft--switching can be achieved in a wider range of 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
Top Related