POWER ELECTRONICS

CIRCUITS, DEVICES, AND APPLICATIONS

Eng.Mohammed Alsumady

04/18/23 2

EPE 352POWER ELECTRONICS

DC-DC CONVERTERS

04/18/233

Step Down Converter

11

( ) ( )

( ) /

ss

o average S o rms S

S S

o average S

tk t f

T

V kV V k V

V V RR

I kV R k

• Constant frequency operation

•Variable frequency operation

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PWM Waveform Generation

rr

cr

r

Vv t

TV

kV

• which is also called the modulation voltage, M

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Step Down Operation with RL Load

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Step Down Operation with RL Load

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Modes of Operation

22

2 2

/ /2 2

2 2 3 3 1

0

( 0)

( ) 1

( (1 ) )

tR L tR L

diRi L E

dtFor i t I

Ei t I e e

Ri t t k T I I I

11

1 1

/ /1 1

1 1 2

( 0)

( ) 1

( )

S

tR L tR LS

diV Ri L E

dtFor i t I

V Ei t I e e

Ri t t kT I

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Modes of Operation

/ /2 1

(1 ) / (1 ) /3 1 2

1

(1 ) 1

kTR L kTR LS

k TR L k kTR L

V EAt t kT I I e e

RE TR T

At t k T I I I e e zR L

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Discontinuous Operation

22 1

1 1 kzS

RILt ln

R E

V ELln e

R E

1

/1

1 1 2

2

0

( ) 1

( )

1

tR LS

kzS

I

V Ei t e

Ri t t kT I

V EAt t kT I e

R

• For a continuous load current

1

10 0

1

10

1

1

1

kzS

z

kz

zS

kz

zS

V e EFor I

R e R

e E

e V

E ewhich gives x

V e

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Step-Up Operation

1S

L

Vdiv L I t

dt L

• The average output voltage

1

2 2

1

1

1

o S S

S

tIv V L V

t t

Vk

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Step-Up Operation 1

1 1

1

( )

0 0

SS

S

VdiV L i t t I

dt Ldi

For Vdt

22 2

2

( )

0

SS

S

V EdiV L E i t t I

dt Ldi

For V Edt

• For controllable power

0 SV E

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Step-Up Operation 1

1 1

2 1 1

( )

( )

SS

S

VdiV L i t t I

dt LV

I i t kT kT IL

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Converter Classifications • 1st Quadrant converter

• 2nd Quadrant converter

• 1st and 2nd quadrant

• 3rd and 4th quadrant

• Four-quadrant

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1st Quadrant Converter • Both the voltage and the current are positive

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2nd Quadrant Converter •The voltage is positive and the current is negative

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2nd Quadrant Converter

/ /1

1 1 2

0

( ) 1

( )

LL

tR L tR LL

L

diL Ri E

dtE

i t I e eR

At t t kT i t t kT I

/ /2

2 2 1

(1 )

1 2

( ) 1

(1 ) ( (1 ) )

1

1 1

LS L

tR L tR LSL

L

k z kz zS S

z z

diV Ri L E

dtV E

i t I e eR

At t t k T i t t k T I

V Ve E e e EI I

R e R R e R

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1st and 2nd Quadrant Converter• S1 and D4

• S4 and D1

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18

3rd and 4th Quadrant Converter• S3 and D2

• S2 and D3

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Four Quadrant Converter

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Switching Mode Regulators

• Buck Regulator

• Boost Regulator

• Buck-Boost Regulator

•Cuk Regulator

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Buck Regulator

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Buck Regulator

2

(1 )

(1 )

8 8

a S S a

S

SC

V kV I kI

V k kI

fL

V k kIV

fC f CL

• The critical values for a continuous inductor current and

capacitor voltage

2

(1 )

2

1

16

c

c

k RL L

f

kC C

Lf

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Boost Regulator

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Boost Regulator

1 1

S a Sa S

a a S aC

a

V I V kV I I

k k fL

I V V I kV

V fC fC

• The critical values for a continuous inductor current and capacitor voltage

1

2

2

c

c

k k RL L

f

kC C

fR

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Buck-Boost Regulator

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Buck-Boost Regulator

1 1

( )

S a Sa S

a a aC

a S

kV kI V kV I I

k k fL

I V I kV

V V fC fC

• The critical values for a continuous inductor

current and capacitor voltage

1

2

2

c

c

k k RL L

f

kC C

fR

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Cuk Regulator

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Cuk Regulator

1 21 2

11 1

2 2 22 2 2 2

1 1

1

( )

(1 )

8 8

S aa S

S S

SS SC

S a

a SC

kV kIV I

k kV k V k

I IfL fL

I kI VV

V V fC fC

V k kVV

C L f C L f

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Cuk Regulator•The critical values for a continuous inductor

current and capacitor voltage

2

1 1

2 2

1 1

2 2

1

2

1

2

2

1

8

c

c

c

c

k RL L

kf

k RL L

f

kC C

fR

C CfR

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Rectified Fed Converter

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Input Filter

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Summary • A dc-dc can convert a fixed dc voltage to a variable dc voltage. • A four-quadrant converter allows power flow to and from load. • Switching mode converter can produce output voltage higher and lower than the input voltage. • The rectifier fed boost converter is commonly used for unity power factor correction (UPFC).