technique for llc series resonant dc/dc converter low power group technique for llc series resonant...

Technique for LLC Series Resonant DC/DC Converter

Low Power Group



Low Power Group

Contents:

1. Problems of Conventional DC/DC Converter

2. Principle of Proposed LLC-SRC

3. Experimental Verification

4. Application Examples

5. Conclusions


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S1

S2

VinVo

TrCd

D2

D1

Ld

S1

S2

TrCd

D2

D1

Ld

S3

S4Lr

VinVo

Forward Asymmetrical H/B Phase Shift F/B

S

n:1 VoVin

D2

D1

Ld

Duty cycle

Conversion efficiency Input voltage

Low Input High Input

Voltage spike

di/dt

iD

Problems of Conventional PWM Converter

Efficiency declines when high input Reverse recovery problem for rectifier


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Problems of Conventional Resonant Converter

Large frequency variation

Failure at no load

Small frequency variation

High circulation energy

Lower circulation energy

Efficiency optimized at low input

sC sL

oR

oVVin

Series resonant

PC

sLoV

Vin

dC

Parallel resonant

PC

sLoV

Vin

sC

LCC series parallel resonant


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Principle of LLC-SRC

Ls

Cs

C1

S1

S2

Tr D1

D2

C2

VinVo

Lm

Proposed Half-bridge LLC Series Resonant Converter (LLC-SRC)


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Comparison with Conventional SRC

1

fsfm

LLC-SRC (Lm=3~7Ls)

Conventional SRC

frequency

Gain=OUT/IN

Ls

LLC-SRC

IN

Cs

LoadLmOUT

Conventional SRC

Ls

IN

Cs

Load

OUT

ZVS operation range:

• Conventional SRC: f>fs

• LLC-SRC: f>fm

fm<f<fs ZCS for rectifiers


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Operation Waveforms:

S1

S2

iLs

iLd

fm<f<fs

imIm

vAB

Ls

Cs

C1

S1

S2Tr

iC1

iLs

D1

D2

C2

iLd

Lmim


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S1

S2

iLs

iLd

f=fs

im

vAB

Ls

Cs

C1

S1

S2Tr

iC1

iLs

D1

D2

C2

iLd

Lm


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S1

S2

iLs

iLd

im

vAB

Ls

Cs

C1

S1

S2Tr

iC1

iLs

D1

D2

C2

iLd

Lm

f>fs


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ss

mino TT

nC

I

n

VV

42

Regulation Equation of LLC-SRC:

sTT

n

VV in

o 2

LsCs

nVo

n

VV in

o 2

n

VV in

o 2

n

VV in

o 2

Vin/2 nVo Vin/2 nVo Vin/2 nVo

Vin/2RLm

f<fs

f=fs

f>fs


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Experimental Verification

Ls

Cs

C1

S1

S2 Tr

iC1

iLs

D1

D2

C2

iLbS1 , S2: IRF3710D1& D2: 40CPQ60Core EE32/16/9n: 6 : 6 Cs: 1.6uFLs: 1uH (leakage inductance)Lm: 6uH

SPECIFICATIONS: INPUT: 40 V - 60 V OUTPUT: 24 V / 10 A Frequency: 75kHz Higher

PARAMETER SELECTION:

Test Circuit


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Driver signal of switch

Vds of the switch

Resonant Current

Voltage of output diode

1: Vgs of bottom switch, 10V/div 2: Vds of bottom switch, 50V/div

3: Ir, resonant current, 25A/div 4: Voltage of output diode, 40V/div

Vin=40V

f=94kHz < fs (125kHz)

Measured operation waveforms


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Resonant Current is close to sine wave.



Vin=50V

f=112kHz ~ fs



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Voltage overshot.ZCS condition was lost.



Vin=60V

f=133kHz > fs



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90

90.5

91

91.5

92

92.5

93

Input Voltage(V)

Effi

cien

cy (

%)

n=6:6 91.4 92.3 92.2

n=6:5 90.8 91.7 92.5

Asy. H/B 91.1 90.8 90.4

40 50 60

Efficiency of test circuit: Vin=40~60V, Vo=24V

@24V/10A

Output


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Application for holdup time requirement

Ls

Cs

C1

S1

S2

C3Tr D1

D2

1kW, 400V input and 54V/20A output sever powerS1,S2: IRFP37N50A D1,D2: 30CPQ150 Tr: EE42/20 – 3C85


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Input Range Ls Cs Lm n

A 300~400V 20uH 88uF 120uH 20:5

B 200~400V 20uH 108uH 50uH 17:5

Parameters of Two Designs:


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91

92

93

94

95

96

97

Input Voltage (V)

Eff

icie

ncy

(%

)

Asy.H/B 95.1 94.2

A 94.6 95.4 96.1

B 91.8 93.2 94.2 95 95.2

200 250 300 350 400

Tested Efficiency (1kW, 54V/20A)

A: 300V~400V input design

B: 200V~400V input design


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60

80

100

120

140

160

Input Voltage(V)

Fre

quen

cy (

kH

z)

0A

20A

0A 81 90 102 119 146

20A 76 85 94 106 123

200 250 300 350 400

Frequency Variation Rang:

@54V output


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1kW, 400V input and 54V/20A output

Transformer

Primary switches

Output Rectifier

Output Capacitors


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CsC1

S1

S2

S3

S4

D2

C3

Tr

C2

D1

Ls

Application for high power and high input voltage

Full-Bridge Structure High input voltage

Ls

CsC1

S1 S3

S2 S4 Tr

D1

D2

C3


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Conclusions:

Features of LLC-SRC:

Simple and flexible structure

ZVS for switches and ZCS for rectifiers

Conversion efficiency optimized at high input

Applications: High input voltage

Higher output voltage

Holdup time requirement

technique for llc series resonant dc/dc converter low power group technique for llc series resonant...

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