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Hindawi Publishing CorporationAdvances in Power ElectronicsVolume 2012, Article ID 730473, 10 pagesdoi:10.1155/2012/730473

Research ArticleEmbedded Controlled Isolated BidirectionalFull-Bridge DC-DC Converter with Flyback Snubber

D. Kirubakaran 1 and Rama Reddy Sathi 2

1 EEE Department, St. Joseph’s Institute of Technology, A ffiliated to Anna University , Chennai-600119, India 2 Jerusalem College of Engineering, Anna University Chennai, Chennai 600 100, India

Correspondence should be addressed to D. Kirubakaran, kiruba d@yahoo.com

Received 10 May 2012; Revised 16 July 2012; Accepted 31 July 2012

Academic Editor: C. M. Liaw

Copyright © 2012 D. Kirubakaran and R. R. Sathi. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

An isolated bidirectional full-bridge DC-DC converter with yback snubber for supplying a resistive load is simulated and experi-mentally veried. The DC-DC converter for high conversion ratio, high output power, and soft start-up capability is presentedin this paper. The circuit consists of a capacitor, a diode, and a yback converter. These components help to clamp the voltagespikes caused by the current di ff erence between the current fed inductor and leakage inductance of the isolation transformer. Theswitches are operated by soft-switching technology. The suppression of inrush current which is usually found in the boost modestart-up transition is presented here. The simulated and experimental results for output voltage, output current, and power forboth buck and boost modes are presented.

1. Introduction

A DC-DC converter converts a source of direct current(DC) from one voltage level to another. These convertersare important in portable electronic devices such as cellularphones and laptop computers, which are supplied withpower from batteriesprimarily. The ordinary circuit of a DC-DC converter for high power applications typically includesa bidirectional full-bridge DC-DC converter [ 1–3]. The cur-rent diff erence between the inductor and isolation trans-former does not ensure a well-dened output voltage andis characterized by less reliability and effi ciency. The outputvoltage contains voltage spikes. An active commutation canbe used to control the current in the leakage inductance [ 4].But it requires an additional clamping circuit to suppressthe voltage spikes. An RCD passive snubber can be used toclamp the voltage. A buck converter was employed to replaceRCD snubber. But it still needed complex clamping cir-cuit [5, 6]. Active clamping increases the current stress onswitches. Soft-switching capability can be used, but it is notsuitable for step-down operation.

In this scheme of DC-DC converter with yback snubber(Figure 1), the snubber recycles the absorbed energy in the

clamping capacitor. The voltage of the clamping capacitorcan be regulated by operating the yback snubber inde-pendently. The current does not circulate through the full-bridge switches, and hence the current stress can be reduced,improving the system reliability signicantly.

2. Conguration and Operation

The operating principle of the circuit consists of two modes:

(i) step-up conversion,(ii) step-down conversion.

The modes of operation of boost mode are shown inFigure 2 and of buck mode in Figure 4. The theoreticalwaveform for boost and buck modes is shown in Figures 3and 5, respectively. Initiallyall components are assumed to beideal, and the transformer is treated as an ideal transformerassociated with leakage inductance.

2.1. Step-Up Conversion

Interval 1: t 0 ≤ t < t 1. The equivalent circuit is shown inFigure 3(a) . All the four switches M 1 and M 4 are turned ON.

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p

+

+

−

−−

−

V LV

Lm

D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

L1

i p is

N p : N s

D4D2

Lh

iHV

D8D6 M 8 M 6

Figure 1: Isolated bidirectional full-bridge Dc-Dc converter with yback snubber.

t 0 t 1 t 2 t 3 t 4 t 5

V gsV gsV gsV gs

V AB

I p

V ds

I ds

V c

V gs

I ds

( M 1)( M 4)( M 2)( M 3)

( M 4)

( M 4)

( M 5)

( M 5)

Figure 2: Operational waveform of step-up conversion.

In this interval, the inductor Lm is charged by V LV and thecurrent iL increases linearly. The primary windings of thetransformer are short circuited.

Interval 2: t 1 ≤ t < t 2. The equivalent circuit is shown inFigure 3(b) . At t 1, M 1 and M 4 are conducting while M 2 and M 3 are turned OFF. Clamping diode DC conducts until thecurrent di ff erence ( iL(t 2) − i p(t 2)) drops to zero. D5 and D8conduct to transfer power. The current di ff erence ( iL(t ) −i p(t )) ows into clamping capacitor C c.

Interval 3: t 2 ≤ t < t 3. The equivalent circuit is shown inFigure 3(c) . At t 2, DC stops conducting and yback snubber

starts to operate. Clamping capacitor C c. is discharging andyback conductor stores energy. M 1 and M 4 in ON state andD5 and D8 remain ON to transfer power.

Interval 4: t 3 ≤ t < t 4. The equivalent circuit is shown inFigure 3(d) . At t 3, the energy stored in yback conductoris transferred to high-voltage side. The yback snubberoperates to regulate V LV to V c to V c(R) same switches operatesto transfer power from V LV to V HV .

Interval 5: t 4 ≤ t < t 5. The equivalent circuitis shown in Figure 3(e). At t 4, we obtain aregulated voltage V c(R) . The main power stage

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p

+

+

−

−

−

V LV

Lm

D

D

s

ic

iL

D

A

B

C

c

+

V H

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

L1

i p is

N p : N s

D4D2

Lh

iHV

D8D6 M 8 M 6

(a) Mode I ( t 0 − t 1)

p

+

+

−

−

−

V LV D

D

s

ic

iL

D

A

B

C

c

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

L1

i p is

N p : N s

D4D2

Lh

iHV

D8D6 M 8 M 6

(b) Mode II ( t 1 − t 2)

p

+

+

−

−

−

V LV

Lm

D

D

s

ic

iL

D

A

B

C

c

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

L1

i p is

N p : N s

D4D2

Lh

iHV

D8D6 M 8 M 6

(c) Mode III ( t 2 − t 3)

Figure 3: Continued.

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p

+

+

−

−−

−

V LV

Lm

D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7

M 5D1 D3 D7D5

L1

i p is

N p : N s

D4D2

Lh

iHV

D8D6 M 8 M 6

(d) Mode IV ( t 3 − t 4)

p

+

+

−

−−

−

V HV

Lm

D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

L1

i p is

N p : N s

D4D2

Lh

iHV

D8D6 M 8 M 6

(e) Mode V ( t 4 − t 5)

Figure 3: Equivalent circuit for step-up conversion.

t 0 t 1 t 2 t 3 t 4 t 5

iS2iS1

V CD

iS

M 5

M 6 M 7 M 8

Figure 4: Operation waveforms of step-down conversion.

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p

+

+

−

−−

−

V LV D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

i p is

N p : N s

D4D2

Lm

iHV

D8D6 M 8 M 6

(a) Mode I ( t 0 − t 1)

p

+

+

−

−−

−

V LV D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

i p is

N p : N s

D4D2

Lm

iHV

D8D6 M 8 M 6

(b) Mode II ( t 1 − t 2)

p

+

+

−

−

−

−

V LV D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

i p is

N p : N s

D4D2

Lm

iHV

D8D6 M 8 M 6

(c) Mode III ( t 2 − t 3)

Figure 5: Continued.

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p

+

+

−

−

−

−

V LV D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

i p is

N p : N s

D4D2

Lm

iHV

D8D6 M 8 M 6

(d) Mode IV ( t 3 − t 4)

p

+

+

−

−

−

−

V LV D

D

s

ic

iL

D

A

B

C

c

+

+

V HV

V HV C HV

T s T x

N 2 N 1

M

N

sC c

C f

V c M 2 M 4

M 1 M 3 M 7 M 5D1 D3 D7D5

i p is

N p : N s

D4D2

Lm

iHV

D8D6 M 8 M 6

(e) Mode V ( t 4 − t 5)

Figure 5: Equivalent circuit for step-down conversion.

is still transferring power from V LV to V HV .It stops at t 5 and a half switching cycle operation is com-

pleted. 2.2. Step-Down Conversion

Interval 1: t 0 ≤ t < t 1. The equivalent circuit is shown inFigure 5(a) . At t 0, M 5 and M 8 are turned ON. The V HV isimmediately excited on the transformer and the whole volt-age is exerted on Leq. The transformer current increaseslinearly towards the load current at t 1. M 1 and M 4 conductto transfer power.

Interval 2: t 1 ≤ t < t 2. The equivalent circuit is shownin Figure 5(b) . At t 1, M 8 remains conducting while M 5 isturned OFF. D6 conducts the freewheeling leakage current.

The transformer current reaches the load current level at t 1.DC conducts the resonant Leq and the clamping capacitor

Cc.Interval 3: t 2 ≤ t < t 3. The equivalent circuit is shown inFigure 5(c) . At t 2, with diode D6 conducting, M 6 is turnedON with zero voltage switching.

Interval 4: t 3 ≤ t < t 4. The equivalent circuit is shown inFigure 5(d) . At t 3, M 6 remains conducting while M 8 is turnedOFF. The diode D7 starts to conduct the freewheeling leakagecurrent.

Interval 5: t 4 ≤ t < t 5. The equivalent circuit is shown inFigure 5(d) . At t 4, with D7 conducting, M 7 is turned ONwith ZVS. Over this interval, the active switches change to

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141210

8642

V o l

t a g e

( V )

0.3381 0.3381 0.3381 0.3381 0.3381 0.3381 0.3381Time (s)

(a)

2

1

0

− 1

− 2

V o l

t a g e

( V )

2

1

0

− 1

− 2

V o l

t a g e

( V )

0.1171 0.1172 0.1172 0.1172 0.1172 0.1172 0.1173 0.1173Time ( T )

0.1171 0.1172 0.1172 0.1172 0.1172 0.1172 0.1173 0.1173

Time ( T )

(b)

45

40

35

30

25

20

V o l

t a g e

( V )

3 4 5 6 7 8 9 10Time ( T )

(c)

Figure 6: Simulation circuit and results. (a) Input voltage for boost mode. (b) Driving pulse for switches M 1 and M 2. (c) Output voltage forboost mode.

141210

8642

V o l

t a g e

( V )

0.3381 0.3381 0.3381 0.3381 0.3381 0.3381 0.3381Time (s)

(a)

2

1

0

− 1

− 2

V o l

t a g e

( V

)

2

1

0

− 1

− 2

V o l

t a g e

( V )

0.1171 0.1172 0.1172 0.1172 0.1172 0.1172 0.1173 0.1173Time ( T )

0.1171 0.1172 0.1172 0.1172 0.1172 0.1172 0.1173 0.1173Time ( T )

(b)

10

8

6 V o l

t a g e

( V )

Time (s)

(c)

Figure 7: Simulation circuit and results. (a) Input voltage for buck mode. (b) Driving pulse for switches M 1 and M 2. (c) Output voltage forbuck mode.

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Input

Output

Inductor

Resistive loadPIC16F877A

(a) (b)

(c) (d)

Buck mode-output

(e)

100

90

80

70

60

50

η ( %

)

5 10 15 20 25 30× 10− 2iL (A)

Passive RCDActive clampProposed yback

(f)

Figure 8: Hardware layout andresults. (a)Photograph of theprototype converter. (b)Switchingpulse of switch, S1. (c) Transformer primary side voltage. (d) Transformer secondary side voltage. (e) Converter with buck output. (f) Plot of e ffi ciency in step-up mode.

the other pair of diagonal switches, and the voltage andthe transformer reverse its polarity. It stops at t 5 and itcompletes a half switching cycle operation.

3. Simulation

The full-bridge DC-DC converter with yback snubber issimulated using the Matlab Simulink results presented here.The Simulation parameters are shown in Table 1. Scopes are

connected to measure I/P voltage, driving pulses, and O/Pvoltage. Switching pulses are shown in Figure 6(b) .This is theswitching pulse given to the MOSFET switches. The outputvoltage is shown in Figure 6(c).

For the buck mode with resistor as the load, switchingpulsesareshown in Figure 7(b) . Input and the output voltageare shown in Figures 7(a) and 7(c), respectively.

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2

560

560

RA3

1

PIC16F84A

33 pF

560

7

LED

7812

5

RA2

RA1

Driver ICIR2110

12

10

3

2

2

560

0

12

3

22

1 k

10

4

230 V/15 V

3

1

3

6

S4

S1

560

1 k

0

33 pF

1

6

5

0

13

16

Driver ICIR2110

1

S2

S3

1

1 k

RA0

14

0

18

9

7805

15

5

1000

35 V

1 k

17

13 7

9

230 VAC supply

PIC microcontrollerC 8

D1

C 5

D3

D2

D4

C 9

C 4

C 7

C 3

C 6

C 1

C 2

10 µF

47 µF

10 µF

47 µF

47 µF

47 µF

(a)

Start

Port PB0 high

Port PB1 low

Port PB0 low

Port PB1 low

Port PB0 low

Port PB1 high

Initialize PIC

its clock frequency

Delay 8 µS

Delay 8 µS

Delay 8 µS

Delay 8 µS

microcontroller and

PB0 and PB1

(b)

Figure 9: (a) PIC-based control circuit. (b) Flow chart.

Table 1: Simulation parameters.

Input voltage V in 15 (V)Output voltage V o 33 (V)Switching frequency F s 8 (kHz)Filter capacitor C 1 2200 (µF)Flyback capacitor C 2 100 (µF)Main inductor L1 20 (µH)Filter inductor L2 5 (µH)

ThePIC16F876S microcontroller canbe used to generatethe driving pulse for MOSFET switches. Thus the PIC circuitacts as the control circuit.

4. Experimental Results

The input 230V is stepped down to 15 V using a step-downtransformer and it is rectied to DC by the bridge rectier.In boost mode, the output of the rectier is boosted by a

step-up transformer of ratio 1 : 2. The output is convertedinto ac by an inverter. The load used is a resistive load of rating 1 K, 10 W. The output of the yback converter is fedto the load through a series connection. The output in boostmode is 35 V. In buck mode, the input 15 V is stepped downto 8 V. Figure 8(a) shows the photograph of the prototypeconverter with boosted output. The switching frequency is20 KHz and the switching pulse of switch, S1, is shown inFigure 8(b) . The primary side voltage of the transformeris measured to be 15 V. In the boost mode it is boostedto 30V and it is shown in Figure 8(c). The output of thebuck mode is shown in Figure 8(e). The output is measuredusing a multimeter and it is 8.5 V. Figure 8(f) shows the plotof conversion effi ciency of the bidirectional converter withvarious snubbers operated in the step-up mode.

It can be observed that the conversion e ffi ciency of theproposed converter is around 90–92%, which is higher thanthe other types.

The PIC 16X7X-based control circuit is shown inFigure 9(a) . The microcontroller is used to generate driving

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pulses for the MOSFET switches. They are amplied usingthe driver IC IR2110. The gate signal is connected to port pinP1.0. Various steps involved in the ring pulse generation areshown in Figure 9(b) .

5. Conclusion

An isolated bidirectional full-bridge DC-DC converter trans-former converter had voltage spikes due to the current dif-ference between the current fed inductor and leakage induc-tance of the isolation transformer.This voltage spikehasbeenalleviated by the yback snubber. The yback snubber canbe controlled to attain a soft start-up feature. The currentstress is reduced under heavy load conditions. This converterhas also the advantage of increased reliability and e ffi ciency.The simulation demonstrates the actual converter capability to alleviate voltage spikes and to improve the e ffi ciency.

References

[1] H. Bai and C. Mi, “Eliminate reactive power and increase sys-tem efficiency of isolated bidirectional dual-active-bridge DC-DC converters using novel dual-phase-shift control,” IEEE Transactions on Power Electronics, vol. 23, no. 6, pp. 2905–2914,2008.

[2] B. Bai, C. C. Mi, and S. Gargies, “The short-time-scale transientprocesses in high-voltage and high-power isolated bidirectionalDC-DC converters,” IEEETransactions on Power Electronics, vol.23, no. 6, pp. 2648–2656, 2008.

[3] C. Zhao, S. D. Round, and J. W. Kolar, “An isolated three-portbidirectional DC-DC converter with decoupled power ow management,” IEEE Transactions on Power Electronics, vol. 23,no. 5, pp. 2443–2453, 2008.

[4] T. Reimann, S. Szeponik, G. Berger, and J. Petzoldt, “Novelcontrol principle of bi-directional DC-DC power conversion,”in Proceedings of the 28th Annual IEEE Power Electronics Spe-cialists Conference (PESC ’97), vol. 2, pp. 978–984, June 1997.

[5] C. Qiao and K. M. Smedley, “An isolated full bridge boostconverter with active soft switching,” in Proceedings of the IEEE 32nd Annual Power Electronics Specialists Conference, pp. 896–903, June 2001.

[6] L. Zhou and X. Ruan, “A zero-current and zero-voltage-switch-ing PWM boost full-bridge converter,” in Proceedings of theIEEE 34th Annual Power Electronics Specialists Conference, pp.957–962, June 2003.

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