power electronics chapter 5 dc to dc converters (choppers)
TRANSCRIPT
Power ElectronicsPower Electronics
Chapter 5
DC to DC Converters
(Choppers)
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OutlineOutline
5.1 5.1 Basic DC to DC convertersBasic DC to DC converters
5.2 5.2 Composite DC/DC converters and Composite DC/DC converters and
connection of multiple DC/DC convertersconnection of multiple DC/DC converters
5.3 5.3 Isolated DC to DC convertersIsolated DC to DC converters (Indirect DC (Indirect DC to DC converters )to DC converters )
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5.1 5.1 Basic DC to DC convertersBasic DC to DC converters
5.1.1 Buck converter (Step-down converter)5.1.1 Buck converter (Step-down converter)
5.1.2 Boost converter (Step-up converter)5.1.2 Boost converter (Step-up converter)
5.1.3 Buck-Boost converter (Step-down/step-5.1.3 Buck-Boost converter (Step-down/step- up converter) and Cuk converter up converter) and Cuk converter
5.1.4 Sepic converter and Zeta converter5.1.4 Sepic converter and Zeta converter
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5.1 Basic DC to DC converters5.1 Basic DC to DC converters
Introduction—Buck converterIntroduction—Buck converter
SPDT switch changes SPDT switch changes dc componentdc component
Switch output Switch output voltage waveformvoltage waveform
Duty cycle D: Duty cycle D: 0 0 D D 11
complement D’:D’ = 1 - D
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Dc component of switch output voltageDc component of switch output voltage
Fourier analysis: Dc component = average value
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Insertion of low-pass filter to remove switching Insertion of low-pass filter to remove switching harmonics and pass only dc componentharmonics and pass only dc component
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Basic operation principle of buck converterBasic operation principle of buck converter
Buck converter Buck converter with ideal switchwith ideal switch
Realization Realization using power using power MOSFET and MOSFET and diodediode
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Thought process in analyzing basic Thought process in analyzing basic DC/DC convertersDC/DC converters
Basic operation principle (qualitative analysis)Basic operation principle (qualitative analysis)– How does current flow during different switching statesHow does current flow during different switching states
– How is energy transferred during different switching statesHow is energy transferred during different switching states
Verification of small ripple approximationVerification of small ripple approximation
Derivation of inductor voltage waveform during different Derivation of inductor voltage waveform during different
switching statesswitching states
Quantitative analysis according to inductor volt-second Quantitative analysis according to inductor volt-second
balance or capacitor charge balancebalance or capacitor charge balance
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Actual output voltage waveform of buck converter
Buck converterBuck convertercontaining practicalcontaining practicallow-pass filterlow-pass filter
Actual output voltageActual output voltagewaveformwaveform
vv((tt) = ) = V V + + vvrippleripple((tt))
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The small ripple approximationThe small ripple approximation
vv((tt) = ) = V V + + vvrippleripple((tt))
In a well-designed converter, the output voltage In a well-designed converter, the output voltage ripple is small. Hence, the waveforms can be ripple is small. Hence, the waveforms can be easily determined by ignoring the ripple:easily determined by ignoring the ripple:
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Buck converter analysis:Buck converter analysis:inductor current waveforminductor current waveform
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Inductor voltage and currentInductor voltage and currentsubinterval 1: switch in position 1subinterval 1: switch in position 1
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Inductor voltage and currentInductor voltage and currentsubinterval 2: switch in position 2subinterval 2: switch in position 2
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Inductor voltage and current waveformsInductor voltage and current waveforms
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Determination of inductor Determination of inductor current ripple magnitudecurrent ripple magnitude
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Inductor current waveform Inductor current waveform during start-up transientduring start-up transient
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The principle of inductor The principle of inductor volt-second balance: Derivationvolt-second balance: Derivation
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Inductor volt-second balance:Inductor volt-second balance:Buck converter example Buck converter example
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The principle of capacitor charge The principle of capacitor charge balance: Derivationbalance: Derivation
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Boost converter exampleBoost converter example
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Boost converter analysisBoost converter analysis
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Subinterval 1: switch in position 1Subinterval 1: switch in position 1
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Subinterval 2: switch in position 2Subinterval 2: switch in position 2
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Inductor voltage and capacitor current Inductor voltage and capacitor current waveformswaveforms
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Inductor volt-second balanceInductor volt-second balance
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Conversion ratio Conversion ratio M(D) M(D) ofofthe boost converterthe boost converter
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Determination of inductor current Determination of inductor current dc componentdc component
Continuous-Conduction-Mode (CCM) and Continuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) of buckDiscontinuous-Conduction-Mode (DCM) of buck
E
V
+
-
M
RL
VD
io
EMuo
iG
t
t
tO
O
O
T
E
iGton
toff
io i1 i2
I10 I20
t1uo
CCM
O
O
O t
t
t
T
E E
iG
iG
ton
toff
iotx
i1 i2
I20t1 t2
uo
EM
DCM
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Continuous-Conduction-Mode (CCM) and Continuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) of boostDiscontinuous-Conduction-Mode (DCM) of boost
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EM
V DL
V
a )
EMu o
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5.2 Composite DC/DC converters and 5.2 Composite DC/DC converters and connection of multiple DC/DC convertersconnection of multiple DC/DC converters
5.2.1 A current-reversible chopper5.2.1 A current-reversible chopper
5.2.2 5.2.2 Bridge chopper (H-bridge DC/DC Bridge chopper (H-bridge DC/DC converter) converter)
5.2.3 Multi-phase multi-channel DC/DC 5.2.3 Multi-phase multi-channel DC/DC converters converters
5.2.1 5.2.1 A current reversible chopperA current reversible chopper
E L
V 1
V D 1 u o
ioV 2
V D 2
EMM
R
31
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Can be considered as aCan be considered as a combination of a Buck and combination of a Buck and a Boost a Boost
Can realize two-quadrant ( Can realize two-quadrant ( I & III & II)) operation of DC motor: operation of DC motor: forward motoring, forward motoring, forward braking forward braking
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Bridge chopper (H-bridge chopper)Bridge chopper (H-bridge chopper)
Can be considered as the combination of two Can be considered as the combination of two current-reversible choppers. current-reversible choppers.
Can realize 4-quadrant operation of DC motor.Can realize 4-quadrant operation of DC motor.
E L R
+ -
V1
VD
1
uoV3
EM
V2
VD
2
io
V4
VD
3VD
4
M
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Multi-phase multi-channel DC/DC converter
tO
t
t
t
t
t
t
t
O
O
O
O
O
O
O
u1
u2
u3
uo
i1
i2
i3
io
Current output capability is Current output capability is increased due to multi-channel increased due to multi-channel
paralleling. paralleling.
Ripple in the output voltage and Ripple in the output voltage and
current is reduced due to multi- current is reduced due to multi- channel paralleling. channel paralleling.
Ripple in the input current is Ripple in the input current is reduced due to multi-phase reduced due to multi-phase paralleling. paralleling.
C
L
E M
V1
V2
V3
i1
i2
i3
VD3 VD2
L1
L2
L3
io
uo
u1u2u3
VD1
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5.3 5.3 Isolated DC to DC convertersIsolated DC to DC converters
(Indirect DC to DC converters )(Indirect DC to DC converters )
Reasons to use indirect DC to DC structureReasons to use indirect DC to DC structureNecessary isolation between input and outputNecessary isolation between input and output
In some cases isolated multiple outputs are neededIn some cases isolated multiple outputs are needed
The ratio of input and output voltage is far away from 1The ratio of input and output voltage is far away from 1
Power semiconductor devices usually usedPower semiconductor devices usually usedInverter part: Power MOSFETs, IGBTsInverter part: Power MOSFETs, IGBTs
Rectifier part: Fast recovery diodes, Schottky diodes, Synchronous rRectifier part: Fast recovery diodes, Schottky diodes, Synchronous rectifiersectifiers
InverterInverter TransformerTransformer RectifierRectifier FilterFilterDC inputDC input
ACAC ACACDC outputDC outputHigh frequencyHigh frequency
IsolationIsolation
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Classification of isolated DC to DC convertersClassification of isolated DC to DC converters
Isolated DC to DCconverters
Single-ended converters• Forward converter• Flyback converter
Double-ended converters• Half bridge• Push-pull• Full bridge
According to whether transformer current is uni-direction or bi-directional
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5.3.1 Forward converter5.3.1 Forward converter
Simple, low costSimple, low cost
Uni-polar transformer current, low power applicationsUni-polar transformer current, low power applications
S
u S
iL
i S
O
t
t
t
t
U i
O
O
O++U i
S
VD 1
VD 2
LN 1N 3 N 2
VD 3
U oW 2W 1W 3
T
t
N
N
U
U on
1
2
i
o
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5.3.2 Flyback converter5.3.2 Flyback converter
Simple, low costSimple, low cost
Uni-polar transformer current, low power applicationsUni-polar transformer current, low power applications
++
U i
S
VDN 1 N 2U oW 1
W 2
S
u S
i S
iVD
t on t offt
t
t
t
U i
O
O
O
O
off
on
1
2
i
o
t
t
N
N
U
U
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5.3.3 Half bridge converter5.3.3 Half bridge converter
Cost higher than forward and flyback converterCost higher than forward and flyback converter
Bi-polar transformer current, up to several kilowattsBi-polar transformer current, up to several kilowatts
+
+S 1
S 2
VD 1
VD 2
L
U iN 1
N 2
N 3
+u d
U o
+
C 1
C 2
W 1 W 3
W 2
S 1
S 2
u S 1
u S 2
i S 1
i S 2
iD 1
i S 2
t
T t
t
t
t
t
t
t
t on
U i
U i
iL
iL
O
O
O
O
O
O
O
O
T
t
N
N
U
U on
1
2
i
o
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5.3.4 Push-pull converter5.3.4 Push-pull converter
Cost higher than forward and flyback converterCost higher than forward and flyback converter
Center-tapped transformerCenter-tapped transformer
++
S 1
S 2
VD 1
VD 2
L
U i
N 1
N 1'
N 2
N 2' U o
S 1
S 2
u S 1
u S 2
i S 1
i S 2
iD 1
i S 2
t on
T
t
t
t
t
t
t
t
t
2U i
2U i
iL
iL
O
O
O
O
O
O
O
O
T
t
N
N
U
U on
1
2
i
o 2
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5.3.5 Full-bridge converter5.3.5 Full-bridge converter
Cost is even higherCost is even higher
Bi-polar transformer current, up to several hundreds of Bi-polar transformer current, up to several hundreds of
kilowattskilowatts
++N 1
S 2
S 3
S 4
VD 1
VD 2
VD 4
VD 3LS 1
N 2
+
-
+
-
u d
u TU i U o
W 2W 1
S 1(S 4)
S 2(S 3)
u S 1(u S 4)
u S 2(u S 3)
i S 1( i S 4)
i S 2( i S 3)
iD 1( iD 4)
i S 2( i S 3)
t on
T
t
t
t
t
t
t
t
t
U i
U i
iL
iL
O
O
O
O
O
O
O
O
T
t
N
N
U
U on
1
2
i
o 2
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5.3.6 Rectifier circuits in 5.3.6 Rectifier circuits in the isolated DC to DC convertersthe isolated DC to DC converters
+
VD 1
VD 2
L
+
VD 1LVD 3
VD 2VD 4
+
V 1
V 2
L
Full-wave rectifierFull-wave rectifierFull-bridge rectifierFull-bridge rectifier
Synchronous rectifierSynchronous rectifier
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5.3.7 Configuration of switching power suppl5.3.7 Configuration of switching power supplyy
Linear power supplyLinear power supply
42
Regulated Regulated DC outputDC output
Line Line frequencyfrequencyAC inputAC input
InverterInverterFilterFilter TransformerTransformerDCDC
High High frequencyfrequency
ACAC
RectifierRectifier RectifierRectifier FilterFilter
ACAC
High High frequencyfrequency
IsolationIsolation
Indirect DC to DC converterIndirect DC to DC converter
Line Line frequencyfrequencyAC inputAC input
RectifierRectifier FilterFilter Series PassSeries PassRegulatorRegulatorTransformerTransformer
DCDCRegulated Regulated DC outputDC output
Line frequencyLine frequency
IsolationIsolation
Switching power supplySwitching power supply