lec09 convertidores cc-cc con aislamiento2

8/17/2019 LEC09 Convertidores CC-CC Con Aislamiento2

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DC/DC Power Converters

DC/DC switched modeconverters

Topologies with isolation

DC/DC switched modeDC/DC switched modeconvertersconverters

Topologies with isolationTopologies with isolation


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Topologies with transformer

Energy: transferred and stored

Stored energy: magnetizing (Lm) and Leakage (Llk)

Lm is common energy. Located in any winding

Simplified modelSimplified model

d

dt

u

n

u

n

u

n

p

p

φ = = = =

1

1

2

2

....

n i n i1 1 2 2⋅ = ⋅

L

Relmag, i =

ni2


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Square wave converterSquare wave converter inin steady statesteady state

Steady state circuit

n1 : n2

v1 v2

+

-

+

-

vi

= ni

· dΦ/dt

Φ= ΦB - Φ A = (v i/n i)·dt∫

B

A

Faraday´s law:

Steady state:

( Φ)cycle

= 0

Topologies with transformer

V1,avg = V2,avg = 0


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Flyback Flyback (I)(I)

Straight forwardStraight forward


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Flyback Flyback (II)(II)

Transformer behavesTransformer behaves asas twotwo

coupled inductorscoupled inductors

Energy storage

Energy storage

Normally, there is a gapNormally, there is a gap


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Flyback Flyback (III)(III)

VO

+

-

vS

+

-

Vg

+

-v

D

n1 n2

d·T·Vg/n1 - (1-d)·T·VO/n2 = 0

VO = Vg·(n2/n1)·d/(1-d)

vD max = Vg·n2/n1 + VO= Vg·(n2/n1)·/(1-d)

vS max = Vg+VO·n1/n2 = Vg/(1-d)

Voltage stress

Volt. balance


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Flyback vs Buck Flyback vs Buck --BoostBoost

Buck-Boost

50V

2A

100V

1A (avg)

S

D

L

100W

vS max = vD max = 150V

iS=1A iD=2A iL=3A

VAS = 150VA VAD = 200VA

Equal stressEqual stress

vS max = vD max = 150V

iS=1A iD=2A


50V

2A

100V

1A (avg)

S

D

100WFlyback

1:1


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From Buck to Forward

Ue

Us

••

PROBLEM:PROBLEM: transformer demagnetizationtransformer demagnetization

Magnetizing current needs to flow through any winding

Imag


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This is the solutionThis is the solution

Lm

Demagnetizing

Voltage

From Buck to Forward


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Forward converterForward converter (I)(I)

Vg n2

n1

Demagnetization based oninput voltage

V1 = V2 = Vg

Considering:

d’ = d·n2/n1 d’ < 1 - d

then:

d < n1/(n1 + n2) dmax = n1/(n1 + n2)

V1

V2

n2

n1


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Forward converterForward converter (II)(II)

VO

n2:n3

n1

+

-vD2

vS

+

-

vD1

+

-Vg

vS max = Vg+Vg·n1/n2 = Vg/(1-dmax)

vD1 max = Vg·n3/n1

vD2 max = Vg·n3/n2

dmax = n1/(n1 + n2)

Vg·n3/n1 VO

+

-

ON time d·T

VO = d·Vg·n3/n1(in CCM)

VO-

+

OFF time (1-d)·T


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Forward converterForward converter (III)(III)

iD2

VOVg n2:n3

n1

iS

iL

iD1

iD3iO

iD2·n3/n1

T

d·T

t

Vgs

t

iLiO

d’·T

iD3

iD2

iD1

iS

t

t

t

t

iD2 = IO·d iD1 = IO·(1-d)

im = Vg·T·d2/(2·Lm) (from primary)

iS = IO·d·n3/n1 + im iD3 = im


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Buck Buck vsvs ForwardForward

Higher Higher VVSS maxmax inin ForwardForward

Forward

50V

2A

100V

1A (avg)

S

D1

L

100W1 : 1:1

D2D3


iS=1A iD1= iD2=1A

vD1 max= vD2 max= 100V

vS max=200V iL=2A

Buck

50V

100V

2A1A (avg)

S D

L

100W

vS max=vD max=100V

iS

=1A iD

=1A iL

=2A

VAS=100VA VAD=100VA


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Reset windingReset winding (n2)(n2) designdesign

vD2

VO

n2:n3

n1

+ -

vS

+

-

vD1

+

-Vg

Φ

t

v i/n i

t+-

Vg/n1

Φ

max

Vg/n2

Φ

t

v i/n i

t+

-

Vg/n1

Φmax

Vg/n2Low Vg

Φ

t

v i/n i

t+ -

Vg/n1

Φmax

Vg/n’2

Lower stress High Vg


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Two switches

☺ Lower BVdss (Vg)

Two switches

☺ Lower BVdss (Vg)

Forward withForward with 22 switchesswitches

Φ

t

v i/n i

t+

-

Vg/n1

Φmax

Vg/n1dmax = 0.5

VO = d·Vg·n2/n1 (in CCM)

vS1 max = vS2 max = Vg

vD1 max = vD2 max = Vg

vD3 max = vD4 max = Vg·n2/n1

Vg

n1 : n2

S1D4

D3

D1

D2

S2

VO


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Boost with IsolationBoost with Isolation??

•Not possible using just a single switch

• Multiple switch Current fed converters

••Not possibleNot possible using just a single switch

• Multiple switch Current fed converters


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Classical invertersClassical inverters

VOVg

S2S1“Push-pull” VO

Vg

S2

S1

Half Bridge

S2

S1

Vg

S3

S4

VO

Full Bridge

Inverter structures


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DC/DCDC/DC ConvertersConverters based on invertersbased on inverters

“push-pull”

inverter Center tapped “push-pull”

CDR - “ push-pull”Single ended “ push-pull”

Inverter structures


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PushPush--pullpull (I)(I)

Forward Forward

“ push-pull”

B

B

H

B

B

H

Inverter structures


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S2 S1

n1 : n2

n1

n1

n2

n2

Vg

VO

L

•When S2 is ON:

Vg·n2/n1

LVO

• When S1 is ON:

Vg·n2/n1

LVO

When BOTH S1 & S2 are OFF ?

Inverter structures

PushPush--pullpull (II)(II)


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L

VO

iL

D1

D2

iL1

iL2

• Equivalent circuit when

both S1 & S2 are OFF:

•D1 & D2 conduct

Transformer voltage is

zero

• iL1 and iL1 must:

iL1 + iL2 = iLiL1 - iL2 = iLm (sec. trans.)

VOL

Inverter structures

PushPush--pullpull (III)(III)


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•

vD is as a Forward with double frequency and2·d VO = 2·d·Vg·n2/n1 (CCM)

• vsmax = 2·Vg vD1max = vD2max = 2·Vg·n2/n1

S2

n1

n1

n2

n2

Vg

VO

LvD

+

-

S1

+ -

vD1

+ -

vD2

vS1+-

+

-

vS2

D1

D2

t

vS2

t

t

Td·T

t

t

Vgs

t

vS1

vD1

vD2

vD

2·Vg

2·Vg

Vg·n2/n1

2·Vg·n2/n1

2·Vg·n2/n1

S1 S2

dmax = 0.5

Inverter structures

PushPush--pullpull (IV)(IV)


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S2 S1

n1 : n2

n1

n1

n2

n2

Vg

VO

L

iS1

iL

D1

D2

iD1

iD2

iS2

iO

Average currents:

iS1 = iS2 = iO·d·(n2/n1) iD1 = iD2 = iO/2

t

t

t

iL

Vgs

iS2

t

iD1

iS1

t

Td·T

t

iD2

S1 S2

dmax = 0.5

Inverter structures

PushPush--pullpull (V)(V)


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S2 S1

n1

n1Vg

VO

iS1

iS2

• Risk of saturation in “ Voltage Mode”

• “ Current mode” is preferred

B

B

H

Inverter structures

PushPush--pullpull (VI)(VI)


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• vD is as half than in Push-pull

VO = d·Vg·n2/n1 (in CCM)

• vsmax = Vg vD1max = vD2max = Vg·n2/n1

VO

S2

n1

n2

n2Vg

L

vD+

-

S1

+ -

vD1

+ -

vD2

vS1+-

+

-

vS2

D1

D2

Vg/2

Vg/2 t

vS2

t

t

Td·T

t

tVgs

t

vS1

vD1

vD2

vD

Vg

Vg

Vg·0.5·n2/n1

Vg·n2/n1

Vg·n2/n1

S1 S2

dmax = 0.5

Inverter structures

HalfHalf Bridge (I)Bridge (I)


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iD1 iL

S2

n1

n2

n2Vg

LiO

S1

iD2

iS1

iS2

D1

D2

VO

Vg/2

Vg/2

Average currents:


t

t

t

iL

Vgs

iS2

t

iD1

iS1

t

Td·T

t

iD2

S1 S2

dmax = 0.5

Inverter structures

HalfHalf Bridge (II)Bridge (II)


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• Same vD as Push-pull

VO = 2·d·Vg·n2/n1 (in CCM)

• vsmax = Vg vD1max = vD2max = 2·Vg·n2/n1

VO

S3

n1

n2

n2Vg

L

vD+

-

S4

+ -

vD1

+ -

vD2

vS4

+

-

+

-

vS3

D1

D2

S1

S2

vS2, vS3

t

Vgs

t

vS1, vS4 Vg

Vg

t

t

t

Td·T

t

vD1

vD2

vD Vg·n2/n1

2·Vg·n2/n1

2·Vg·n2/n1

S1, S4 S2, S3

dmax = 0.5

Inverter structures

FullFull Bridge (I)Bridge (I)


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Average currents:


iD1 iL iO

iD2

iS4

VO

S3

n1

n2

n2Vg

L

S4

D1

D2

S1

S2

iS3

t

t

t

iL

Vgs

iS2, iS3

t

iD1

iS1, iS4

t

Td·T

t

iD2

S2

, S3

S1, S

4

dmax = 0.5

Inverter structures

FullFull Bridge (II)Bridge (II)


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• Risk of saturation in “ Voltage Mode”

• Solution:• CS in series

• Use “ Current Mode”

S2

S1CS

Vg

VO

S3

S4

Inverter structures

FullFull Bridge (III)Bridge (III)

I t t t


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Vg

vS

iS

Vg

Vg +

-

+

-

+

-

vS

vS

iS

iS

PO

PO

PO

vSmax = 2·Vg iS = PO/(2·Vg)High MOSFET voltage stress

Good only for low Vg

vSmax = Vg iS = PO/VgHigh input current

Good for high Vg

vSmax = Vg iS = PO/(2·Vg)Low stresses

Good for high power

ComparisonComparison

Inverter structures


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DC/DC switched modeconverters

Current fed converters

DC/DC switched modeDC/DC switched modeconvertersconverters

Current fed convertersCurrent fed converters

C rrent fed con erters


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Current fed inverters andCurrent fed inverters and DC/DCDC/DC convertersconverters

“Push-pull”

inverter Full Bridge

inverter

DC/DC Current fed

“Push-pull”DC/DC Current fed

Full Bridge




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t

Vgs of S1

t

Vgs of S2

t

vS2

t

Td·T

t

tvS1

vD1 2·VO

2·VO·n1/n2

2·VO·n1/n2

VO

vD2 2·VOVO

Current fedCurrent fed “ “PushPush--pullpull” ” (I)(I)

Vg+-Vg

VO·n1/n2 VO·n1/n2

Vg+-

Both S1 &

S2 ONS1 OFF S2 OFF

n1

n1

n2

n2Vg

VO

S2S1

+ -

vD1

+

- vD2

vS2+

-

dmin = 0.5




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VoltVolt ..secondsecond balancebalance

VO = Vg·(n2/n1)/2(1-d)

(in CCM)(in CCM)

Vg

S1 & S2ON

+

-Vg

VO·n1/n2

S1 OFF

VO·n1/n2

Vg

+

-S2 OFF

Vg

S1 & S2ON

d·T (1-d)·T

t1 t1t2 t2

1


Current fedCurrent fed “ “PushPush--pullpull” ” (II)(II)



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iL

iO

n1

n1

n2

n2VgS2S1

iD1

iD2

iS2 dmin = 0.5

iS1

Td·T

t

iD1

t

iS2

t

t

iS1

iL

t

Vgs de S1

t

Vgs de S2

iD2iS1 = iS2 = iO·(n2/n1)/4(1-d)

iD1 = iD2 = iO/2


Current fedCurrent fed “ “PushPush--pullpull” ” (III)(III)



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S2S1

iLPossible problem: Provide a path

for inductor current when turningthe converter off (S1 and S2 are

OFF!!)

iL


Current fedCurrent fed “ “PushPush--pullpull” ” (IV)(IV)



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Return energy to input


Current fedCurrent fed “ “PushPush--pullpull” ” (IV)(IV)

Return energy to

output



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Vg VOn1 n2n2 n1

VO Vg

d 1-d

1-d d

Changes

VO = Vg·d

Vg VO

Buck VO = Vg/(1-d)

VgVO

Boost

Voltage fed “ Push-pull”

VO = 2·d·Vg·n2/n1

Vg

VOn1

n1

n2

n2

Current fed “ Push-pull”

VO = Vg·(n2/n1)/2(1-d)

Vg

VOn1

n1

n2

n2


Current fed vs voltage fedCurrent fed vs voltage fed



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Same as Push-pull except

voltage stress in the MOSFET

Same as Push-pull except

voltage stress in the MOSFET


Current fedCurrent fed “ “FullFull BridgeBridge” ” (I)(I)

Return energy to input

Return energy to

output



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Full wave rectifierFull wave rectifier

Current fed “ Push-pull”

Current fed “Full Bridge”


lec09 convertidores cc-cc con aislamiento2

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