Trabalho Conversores DC-DC

7/23/2019 Trabalho Conversores DC-DC

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UNIVERSIDADE DO OESTE DE SANTA CATARINA - UNOESC

Marcelo da Costa

TRABALHO ACDEMICO EXTRACLASSE

CONVERSORES DC-DC

JOAABA

2015


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TRABALHO ACDEMICO EXTRACLASSE

CONVERSORES DC-DC

Relatrio de Eletrnica de Potncia II daOitava fase de Engenharia Eltrica daUniversidade do Oeste de Santa Catarina.

JOAABA

Maio/2015


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1. INTRODUO

Neste trabalho veremos o funcionamento de alguns conversores DC-DC

no isolados, so eles: Conversor Boost, Conversor Ck e conversor Buck-Boost

em cascata. Ser visto suas principais formas de onda e as compararemos comos sinais obtidos atravs de simulaes utilizando o SoftwarePsim. Ainda, ser

realizada uma anlise de correntes e tenses especficas, onde estas grandezas

sero calculadas e comparadas aos dados obtidos atravs da simulao.


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2. FUNDAMENTAO TERICA

2.1 Conversores DC-DC

Como o prprio nome diz conversores DC-DC so circuitos eletrnicos

responsveis por converter um determinado nvel de tenso continua para outro

nvel de tenso tambm continua, sendo a tenso de sada menor ou maior que

a entrada dependendo da topologia adotado. A converso realizada atravs de

um chaveamento da entrada e pela transferncia de energia para a sada, esta

transferncia realizada atravs de elementos semicondutores e

armazenadores, como indutores e capacitores. Os conversores so comumenteencontrados na indstria com em Inversores de Frequncia ou em eletrnicos

portteis.

Os conversores so divididos em duas categorias principais, os isolados e

os no isolados, cada grupo possui vrias topologias. Neste trabalho o foco fica

por conta das seguintes configuraes: Conversor Boost; Conversor Ck;

Conversor Buck-Boost em cascata. Para todos os efeitos adotamos os

conversores como conversores ideais para fins de clculos e teorias, ou seja,

no ser considerado perdas ou saturao de componentes.

2.2 Conversor Boost

O conversor Boost ou Conversor Step-up um conversor elevador de

tenso, pois a tenso na sada igual ou maior a da entrada. A topologia do

conversor vista abaixo, na Figura 1.

Figura 1: Topologia Conversor Boost


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As suas principais caractersticas so de no inverter a tenso de sada,

mantendo a mesma polaridade da entrada; a entrada possui caractersticas de

fonte de corrente, j a sada possui caractersticas de uma fonte de tenso.

So duas etapas de funcionamento deste conversor, a primeira etapa S

est em conduo, o indutor est em srie com a entrada, neste momento ele

armazena energia e no h transferncia de potncia da entrada para a sada.

Na segunda etapa de funcionamento, S est bloqueado e D entra em conduo,

a corrente armazenada no indutor transferida junto com a potncia da entrada,

para a sada. Quando retornamos para a primeira etapa o capacitor

responsvel por manter a tenso constante na sada enquanto o indutor

carregado novamente. O Setp-up pode operar em conduo continua ouconduo descontinua.

As principais formas de ondas esto representadas pela Figura 2 abaixo.

As principais equaes so listadas abaixo:

Figura 2: Formas de Onda do Conversor Boost em Regime Continuo


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1

1

o

in

VM

V D= =

Ganho Esttico

ont

DT

=

Razo cclica

* D

(1 ) 2 * *

o in

M

S

I VIL

D L F= +

Corrente mxima no Indutor

* D

(1 ) 2* *

o in

m

S

I VIL

D L F=

Corrente mnima no Indutor

*

*

o o i

Vo

S o

I V V

F C V

=

Ondulao de Tenso na Sada

2.3 Conversor Ck

O conversor Ck pode diminuir, elevar ou igualar a tenso de sada em

relao a tenso de entrada, ou seja, este conversor pode atuar como um

elevador de tenso ou rebaixador de tenso, basicamente depender da Razo

cclica (D)utilizada no projeto.

Tabela 1: Operao Do Conversor Ck em Funo da Razo Cclica

Razo Cclica OperaoD0,5 Elevador de Tenso

A topologia do Conversor Ck vista abaixo:

Figura 3:Topologia Conversor Ck


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Na primeira etapa de funcionamento, com a chave S fechada, o diodo D

polarizado reversamente bloqueando a passagem da corrente para a sada, oIndutor est em srie com a entrada, causando aumento da corrente que flui pelo

mesmo, esse aumento na corrente armazenada pelo indutor.

Na segunda etapa de funcionamento, a chave S encontra-se aberta, e no

h transferncia de energia da entrada para o indutor, o diodo D polarizado e

passa a conduzir, toda a energia armazenada pelo indutor transferida para a

sada.

Quando o circuito retorna para a primeira etapa, o capacitor C carregado

anteriormente pela energia do indutor, quem garante a tenso constante na

sada.

As principais formas de onda esto representadas abaixo.

Figura 5: Topologia Conversor Buck-Boost


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3. RESOLUO

Neste capitulo ser calculado e simulado os conversores solicitados

conforme anexos.

3.1 Questo 1

Circuito Anexo 1 - Questo 1.

= 11 = 1 2 11 0 . 6 = = = 3050 = . !"# = 1 $ 2 %& = 0.61 0 . 6 $ 120.62 1 2 0 1 0'( 5 0 1 0) *+"- = . /

Figura 8: Valor da corrente mxima Atravs de Simulao

Figura 7: Circuito da primeira questo conversor Boost


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! = 1 2 %& = 0.61 0 . 6 120.62 1 2 0 1 0'( 5 0 1 0) *+ = .

4 = = 78 = / '9 : = 4 = 0 . 6 2 0 1 0'( = / / '4;??@:;A0 0.B12C 2.1 DE/ = .$ / F

4;??@:;A12C 2.120C 0.B DE = . /G Fa)

!HI = 14 JK LMN

O: $ K LMN

N O : P * +QR = / . G

HS = T14 JK ;LMN

O : $ K ;LMN

N O : P * +QU =/.G

Figura 9: Valor da corrente mnima Atravs de Simulao


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b)

O : P * 9QR = .


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c)

4;??@:;A12C 2.1 0.620C 0.B 0.6 DE = . /G F

!HI = 14 JK N

O: $ K LM)N

N O : P * VQR = . W X / '/GHS = T14 JK ;

N; O : $ K ;LM)

NN O : P * VQU = . W / '

Figura 15: Corrente Mdia Sobre a ChaveS Simulado

Figura 14: Corrente Eficaz Sobre o IndutoSimulado

Figura 13: Forma de Onda Sobre a Chave S - Simulado


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3.2 Questo 2

Circuito Anexo 1 - Questo 2.

Figura 18: Corrente Mdia Sobre oCapacitor C Simulado

Figura 17: Corrente Eficaz Sobre oCapacitor C Simulado

Figura 16: Forma de Onda Sobre o Capacitor C - Simulado

Figura 19: Circuito da segunda questo conversor Ck


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1!"# =1!HI $ Z2 = . / 1! =2!HI Z2 =/.X2!"# =2!HI $ Z

2= . 2! =2!HI Z

2=.WX

4;??@:;A0 2._B12C 2.61 DE/ = /.X$ F

4;??@:;A12C 2.6120C 1._B DE = . F

Figura 26: Corrente Mxima Sobre oIndutor L1 Simulado

Figura 25: Corrente Mnima Sobre o IndutoL1 Simulado

Figura 24: Corrente Mxima Sobre oIndutor L2 Simulado

Figura 23: Corrente Mnima Sobre o IndutoL2 Simulado


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c)

b!"# =1!"# $2c"# =\.X b! =1! $2! =.W4;??@:;A0 2.6`12C d._3 DE/ = .W$ /X F

O : P * 9QR =.G


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d)

4;??@:;A0 0.`_012C 2.22 DE/ =.WX/F4;??@:;A

12C 2.6120C 1._B DE

= . F

>!HI = 14 JK LMN

O: $ K LMN

N O:P*VYQR = >HS = T14 JK ;LM

N O : $ K ;LM

NN O:P*VYQU =/.XW

Figura 33: Forma de onda sobre a Chave S - Simulado

Figura 35: Corrente mdia sobre ocapacitor Co Simulado

Figura 34: Corrente Eficaz sobre ocapacitor Co Simulado


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3.3 Questo 3

Circuito Anexo 1 - Questo 3; Anexo 2

Figura 36: Forma de onda sobre Capacitor Co - Simulado

Figura 37: Circuito da terceira questo conversor Buck-Boost em cascata


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Figura 43: Ondulao de corrente presente no capacitor C1 - Ic1

Figura 44: Ondulao de corrente presente no capacitor C2 - Ic2


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b)

Por se tratar de uma configurao mais complexa, de dois conversores

Buck-Boost em cascata, o rendimento se torna menor ao compararmos

com outras topologias. Alm disto os sub circuitos e no linearidade

envolvidos no controle de chaveamento, ajudam a diminuir o

rendimento.

Figura 45: Ondulao de corrente presente na sada - Io


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4. CONCLUSO

Em virtude das informaes levantadas por este trabalho, conclumos que

h uma grande aproximao dos dados obtidos atravs dos clculos e anlises

com os resultados obtidos atravs das simulaes.

Para o Conversor Buck-Boost em cascata, a simulao mostrou-se de

extrema importncia, quando comparados aos dados obtidos experimentalmente

e expostos no artigo. Esta pequena diferena se deve as consideraes, como

componentes ideais.


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ANEXO 1


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UNIVERSIDADE DO OESTE DE SANTA CATARINAREA DAS CINCIAS EXATAS E TECNOLGICASCURSO DE ENGENHARIA ELTRICA FASE8Professor Renato Scortegagna 20-04-2015Eletrnica de Potncia II TAE 1

ALUNO (A): ________________________________________

Orientaes para a Avaliao:I. Entrega do trabalho na data agendada em sala de aulaII. O trabalho deve estar de acordo com a metodologia cientficaIII. Fundamentar teoricamente os circuitos a serem simulados

Bom trabalho!

Apresentao das respostas:I. Valores mdio e rms por meio de clculos.II. Formas de ondas- por meio de simulao.

1 Simular um conversor Boostcomas seguintes especificaes:

Apresente:

a) Valor mdio, eficaz e forma de onda da corrente no indutor.b) Valor mdio, eficaz e forma de onda da corrente na chave.c) Valor mdio, eficaz e forma de onda da corrente no capacitor.

2 Simular um conversor Ckcomas seguintes especificaes:

Apresente:

a) Valor da tenso na sada.b) Valor mdio, eficaz e forma de onda da corrente nos indutores L1e L2.c) Valor mdio, eficaz e forma de onda da corrente na chave.d) Valor eficaz e forma de onda da corrente no capacitor de acumulao C.

3 Simular o conversor do artigo disponibilizado.a) Apresentar as formas de onda propostas pelo autor na Fig. 3. Simular o

conversor para carga com potncia de 100W.b) Aps ler o artigo e se utilizando os seus conhecimentos em eletrnica de

potncia, existe alguma motivao aparente para o baixo rendimento doconversor proposto? Justifique.


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ANEXO 2


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Transformerless High Step-Up DC-DC Converter

Using Cascode Technique

Liang-Jye Shu Tsorng-Juu Liang Lung-Sheng Yang Ray-Lee Lin

Department of Electrical Engineering, National Cheng Kung University

Tainan, Taiwan, R.O.C.

E-mail: [email protected]

AbstractA transformerless high step-up DC-DC converter

is investigated in this paper. Two buck-boost converters are

integrated with single switch. The input voltage of the front

semi-stage is the DC source. The input voltage of the rear semi-

stage is the series of the DC source and the output voltage of the

front semi-stage. Moreover, the output voltage of the proposedconverter is the output voltages of the two semi-stage by

cascode. Thus, high step-up voltage gain can be achieved with

appropriate duty ratio. The operating principle and steady-state

analysis of the proposed converter are discussed in detailed.

Finally, a laboratory prototype circuit is implemented to verify

the performance.

Keywords: buck-boost converter, high step-up voltage gain,

cascode technique.

I. INTRODUCTION

High step-up DC-DC converters are used in many

applications, such as renewable energy conversion,

uninterruptible power supplies (UPS), and high intensitydischarge (HID) lamp for automobile headlamp. Fig. 1shows the fuel-cell electric conversion system. The high step-

up DC-DC converter is required to boost the fuel-cell output

voltage 24 40 V up to 200 V to supply power to the rear

stage - inverter. In order to achieve high voltage gain, the

conventional boost converter must be operated at extremelyhigh duty ratio [1]-[3]. However, due to the impacts of the

parasitic resistive components and the reverse-recovery

problem of the diodes, the conventional boost converter can

not achieve high voltage gain. The DC-DC flyback converter

is a very simple structure with high step-up voltage gain and

electrical isolation. However, the active switch of these

converters will suffer high voltage stress due to the leakageinductance of the transformer [4]. For recycling the energy of

the leakage inductance and minimizing the voltage stress on

the active switch, some energy-regeneration techniques have

proposed to clamp the voltage stress on the active switch and

to recycle the leakage-inductance energy [5]-[7].This paper proposes a transformerless high step-up DC-

DC converter. The high step-up voltage can be achieved by

using the cascode technique. The operating principle is

described in section II. The steady-state analysis of the

proposed converter is discussed in section III. The

experimental results are presented in section IV. Finally, theconclusion is given in section V.

Fig. 1. Fuel-cell electric conversion system.

II. OPERATING PRINCIPLES OF THE PROPOSED CONVERTER

Fig.2 shows the circuit configuration of the proposed

converter, which includes one switch S, three diodes D1, Do1,

and Do2, inductors L1 and L2, and output capacitors Co1 and

Co2. Two buck-boost converters are integrated into the

proposed converter by using single switch. The input voltage

of the front semi-stage is the DC source and the input voltage

of the rear semi-stage comes from the DC source and the

output voltage of the front semi-stage by series. Moreover,the output voltage of the proposed converter comes from the

output voltages of the two semi-stage by cascode. Thus, high

step-up voltage gain can be achieved without extremely large

duty ratio. Some typical waveforms are shown in Fig. 3. In

order to simply the analysis of the operating principle, some

conditions are assumed as follows:

(i) Diodes D1, Do1, and Do2are ideal.

(ii) The capacitors Co1 and Co2 are enough large. Thus, the

output voltage can be considered as constant.When the proposed converter in continuous conduction

mode (CCM), the operating principles are described as

follows:

Mode I:During this time interval [t0, t1], S is turned on. The

equivalent circuit is shown in Fig. 4(a). The energy is

transferred from the DC source to inductor L1through switchS and diode D1. Also, the DC source and capacitor Co1 are

series to release their energies to inductor L2 through switch

S. So, the inductor currents iL1and iL2are increased linearly.Moreover, the energies stored in capacitors Co1 and Co2 are

discharged to the load by series. At t = t1, the mode is end

when switch S is turned off. Thus, the voltages acrossinductors L1and L2are given as

1L inV V (1)

63

The 2010 International Power Electronics Conference

978-1-4244-5393-1/10/$26.00 2010 IEEE


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2 1L in CoV V V (2)

From equations (1) and (2), the inductor currents iL1 and iL2are derived as follows:

1 1 0 0

1

( ) ( ) ( )inL L Vi t i t t t L

(3)

12 2 0 0

2

( ) ( ) ( )in CoL LV V

i t i t t t L

(4)

Mode II:During this time interval [t1, t2], switch S is turned

off. The equivalent circuit is shown in Fig. 4(b). The energiesstored in inductors L1 and L2 are released to the parasitic

capacitor Cds. The energies stored in capacitors Co1 and Co2are discharged to the load by series. At t = t2, the voltage

across capacitor Cds is charged to Vin+VCo1and this mode is

end.

Mode III:During this time interval [t2, t3], switch S is stillturned off. Since the voltage across capacitor Cds is equal to

Vin+VCo1 at t = t2. Then, diode Do1 is ON. The equivalent

circuit is shown in Fig. 4(c). The energy stored in inductor L 2is still released to capacitor Cds. The energy stored in inductor

L1is released to capacitor Co1and the load. Thus, the inductor

current iL1 is decreased linearly. Also, the energy stored incapacitor Co2 is discharged to the load. At t = t3, the voltage

across capacitor Cdsis charged to Vin+Voand the mode is end.

Mode IV:During this time interval [t3, t4], switch S is still

turned off. Since the voltage across capacitor Cds is equal to

Vin+Vo at t = t3. Then, diodes Do1 and Do2 are ON. The

equivalent circuit is shown in Fig. 4(d). The energies storedin inductors L1and L2are released to capacitors Co1, Co2, and

the load. Thus, the inductor currents iL1and iL2are decreasedlinearly. At t = t4, switch S is turned on again and the mode is

end. Thus, the voltages across inductors L1and L2are derived

as follows:

1 1L CoV V (5)

2 2L CoV V (6)

From equations (3) and (4), the inductor currents iL1 and iL2are obtained as

11 3 1 3

1

( ) ( ) ( )CoL LV

i t t t i t L

(7)

22 3 2 3

2

( ) ( ) ( )CoL LV

i t t t i t L

(8)

Fig. 2. Circuit configuration of the proposed converter.

Fig. 3. Typical waveforms of the proposed converter in CCMoperation.

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The circuit specifications and components are selected asinput voltage Vin= 24 V, output voltage Vo= 200 V, output

power Po = 100 W, switching frequency fs = 50 kHz,

capacitors Co1 = Co2= 680 F, inductors L1= 53H, and L2=636H.

Some experimental results are shown in Fig. 7 --- 10.Figs.7 and 8 show some waveforms under the light-load condition

Po= 20 W. It is seen from Fig. 7 that the inductor currents iL1

and iL2are discontinuous, which means thatthe upper cell andthe lower cell of the proposed converter are operated indiscontinuous conduction mode at the light-load condition.

Moreover, the output voltage is well controlled at 200 V. Fig.

8 shows the waveforms of Vgs, iin, iDo1, and iDo2. Figs. 9 and10 show some waveforms under the full-load condition P

o=

100 W. From Fig. 9, one can see that the inductor currents iL1and iL2 are continuous, which means that the upper cell andthe lower cell of the proposed converter are operated in

continuous conduction mode at the full-load condition.

Moreover, the output voltage is well controlled at 200 V. Fig.10 shows the waveforms of Vgs, iin, iDo1, and iDo2. Themeasured results under various load conditions are described

in table I and the curve of the measured efficiency is shown

in Fig. 11. The conversion efficiency is 72.7% at the full-load

condition.

Fig. 6. Prototype circuit of the proposed caocode converter.

Fig. 7. Waveforms of Vgs, iL1,iL2, and Vo at light-loadPo= 20 W.

Fig. 8 Waveforms of Vgs, iin, iDo1, and iDo2at light-load Po= 20 W.

Fig. 9 Waveforms of Vgs, iL1,iL2, and Vo at full-load Po= 100 W.

Fig. 10 Waveforms of Vgs, iin, iDo1, and iDo2at full-load Po= 100 W.

TABLE I

EXPERIMENTAL RESULTS UNDER VARIOUS LOADS

Vin

(V)

Pin

(W)

Vo

(V)

Io

(A)

Po

(W)

(%)

24 29.6 203 0.1 20.3 68.6

24 61.4 202 0.2 40.4 65.8

24 84.7 201 0.3 60.3 71.2

24 111.6 201 0.4 80.4 72

24 137.6 200 0.5 100 72.7

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Fig. 11. Measured efficiency of the proposed converter.

V. CONCLUSIONS

In this paper, a high step-up DC-DC converter is

presented. The circuit topology utilizes cascode technique to

achieve high step-up voltage gain without an extreme dutyratio. Moreover, the proposed converter is also to provide the

function of step-down voltage gain. The operating principleand steady-state analysis are discussed. Finally, a prototype

circuit of the proposed converter is implemented to verify the

performance.

ACKNOWLEDGEMENT

The authors gratefully acknowledge financial support

from the Bureau of Energy, Ministry of Economic Affairs 98-D0204-2 and Research Center of Ocean Environment and

Technology of National Cheng Kung University.

REFERENCES

[1] B. Bryant and M. K. Kazimierczuk, Voltage-loop power-stagetransfer functions with MOSFET delay for boost PWM

converter operating in CCM, IEEE Trans. Ind. Electron., vol.

54, no. 1, pp. 347-353, Feb. 2007.[2] X. Wu, J. Zhang, X. Ye, and Z. Qian, Analysis and derivations

for a family ZVS converter based on a new active clamp ZVScell, IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 773-781,

Feb. 2008.

[3] D. C. Lu, K. W. Cheng, and Y. S. Lee, A single-switchcontinuous-conduction-mode boost converter with reducedreverse-recovery and switching losses, IEEE Trans. Ind.

Electron., vol. 50, no. 4, pp. 767-776, Aug. 2003.

[4] N. Mohan, T. M. Undeland, and W. P. Robbins, PowerElectronics, Third Edition, John Wiley & Sons, Inc., 2003.

[5] N. P. Papanikolaou and E. C. Tatakis, Active voltage clamp in

flyback converters operating in CCM mode under wide loadvariation,IEEE Trans. Ind. Electron., vol. 51, no. 3, pp. 632-640, Jun. 2004.

[6] B. R. Lin and F. Y. Hsieh, Soft-switching zetaflyback

converter with a buckboost type of active clamp, IEEETrans. Ind. Electron., vol. 54, no. 5, pp. 2813-2822, Oct. 2007.

[7] C. M. Wang, A novel ZCS-PWM flyback converter with asimple ZCS-PWM commutation cell, IEEE Trans. Ind.Electron., vol. 55, no. 2, pp. 749-757, Feb. 2008.


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