Hindawi Publishing CorporationAdvances in Power ElectronicsVolume 2012, Article ID 730473, 10 pagesdoi:10.1155/2012/730473
Research Article
Embedded Controlled Isolated BidirectionalFull-Bridge DC-DC Converter with Flyback Snubber
D. Kirubakaran1 and Rama Reddy Sathi2
1 EEE Department, St. Joseph’s Institute of Technology, Affiliated to Anna University , Chennai-600119, India2 Jerusalem College of Engineering, Anna University Chennai, Chennai 600 100, India
Correspondence should be addressed to D. Kirubakaran, kiruba [email protected]
Received 10 May 2012; Revised 16 July 2012; Accepted 31 July 2012
An isolated bidirectional full-bridge DC-DC converter with flyback snubber for supplying a resistive load is simulated and experi-mentally verified. 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 flyback converter. These components help to clamp the voltagespikes caused by the current difference 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 batteries primarily. 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 difference between the inductor and isolation trans-former does not ensure a well-defined output voltage andis characterized by less reliability and efficiency. 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 flyback snubber(Figure 1), the snubber recycles the absorbed energy in the
clamping capacitor. The voltage of the clamping capacitorcan be regulated by operating the flyback 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 significantly.
2. Configuration 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. Initially all components are assumed to beideal, and the transformer is treated as an ideal transformerassociated with leakage inductance.
2.1. Step-Up Conversion
Interval 1: t0 ≤ t < t1. The equivalent circuit is shown inFigure 3(a). All the four switches M1 and M4 are turned ON.
2 Advances in Power Electronics
p
+
+
−
−−
−VLV
Lm
D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2
M4
M1
M3 M7M5D1 D3 D7D5
L1
ip is
Np : Ns
D4D2
Lh
iHV
D8D6 M8M6
Figure 1: Isolated bidirectional full-bridge Dc-Dc converter with flyback snubber.
t0 t1t2 t3 t4 t5
Vgs
Vgs
Vgs
Vgs
VAB
Ip
Vds
Ids
Vc
Vgs
Ids
(M1)
(M4)(M2)
(M3)
(M4)
(M4)
(M5)
(M5)
Figure 2: Operational waveform of step-up conversion.
In this interval, the inductor Lm is charged by VLV and thecurrent iL increases linearly. The primary windings of thetransformer are short circuited.
Interval 2: t1 ≤ t < t2. The equivalent circuit is shown inFigure 3(b). At t1, M1 and M4 are conducting while M2 andM3 are turned OFF. Clamping diode DC conducts until thecurrent difference (iL(t2) − ip(t2)) drops to zero. D5 and D8
conduct to transfer power. The current difference (iL(t) −ip(t)) flows into clamping capacitor Cc.
Interval 3: t2 ≤ t < t3. The equivalent circuit is shown inFigure 3(c). At t2, DC stops conducting and flyback snubber
starts to operate. Clamping capacitor Cc. is discharging andflyback conductor stores energy. M1 and M4 in ON state andD5 and D8 remain ON to transfer power.
Interval 4: t3 ≤ t < t4. The equivalent circuit is shown inFigure 3(d). At t3, the energy stored in flyback conductoris transferred to high-voltage side. The flyback snubberoperates to regulate VLV to Vc toVc(R) same switches operatesto transfer power from VLV to VHV .
Interval 5: t4 ≤ t < t5. The equivalent circuitis shown in Figure 3(e). At t4, we obtain aregulated voltage Vc(R). The main power stage
Advances in Power Electronics 3
p
+
+
−
−
−VLV
Lm
D
D
s
ic
iL
D
A
B
C
c
+
VH
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1M3 M7M5D1 D3 D7D5
L1
ip is
Np : Ns
D4D2
Lh
iHV
D8D6 M8M6
(a) Mode I (t0 − t1)
p
+
+
−
−
−VLV D
D
s
ic
iL
D
A
B
C
c
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2
M4
M1
M3 M7M5D1 D3 D7D5
L1
ip is
Np : Ns
D4D2
Lh
iHV
D8D6 M8M6
(b) Mode II (t1 − t2)
p
+
+
−
−
−VLV
Lm
D
D
s
ic
iL
D
A
B
C
c
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2
M4
M1M3
M7M5D1 D3D7D5
L1
ip is
Np : Ns
D4D2
Lh
iHV
D8D6 M8M6
(c) Mode III (t2 − t3)
Figure 3: Continued.
4 Advances in Power Electronics
p
+
+
−
−−
−VLV
Lm
D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1M3 M7
M5D1 D3 D7D5
L1
ip is
Np : Ns
D4D2
Lh
iHV
D8D6 M8M6
(d) Mode IV (t3 − t4)
p
+
+
−
−−
−VHV
Lm
D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1 M3 M7M5D1 D3 D7D5
L1
ip is
Np : Ns
D4D2
Lh
iHV
D8D6 M8M6
(e) Mode V (t4 − t5)
Figure 3: Equivalent circuit for step-up conversion.
t0 t1 t2 t3 t4 t5
iS2iS1
VCD
iS
M5
M6
M7
M8
Figure 4: Operation waveforms of step-down conversion.
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p
+
+
−
−−
−VLV D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2
M4
M1M3 M7M5D1 D3 D7D5
ip is
Np : Ns
D4D2
Lm
iHV
D8D6 M8M6
(a) Mode I (t0 − t1)
p
+
+
−
−−
−VLV D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1M3 M7M5D1 D3 D7D5
ip is
Np : Ns
D4D2
Lm
iHV
D8D6 M8M6
(b) Mode II (t1 − t2)
p
+
+
−
−−
−VLV D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1M3 M7M5D1 D3 D7D5
ip is
Np : Ns
D4D2
Lm
iHV
D8D6 M8M6
(c) Mode III (t2 − t3)
Figure 5: Continued.
6 Advances in Power Electronics
p
+
+
−
−−
−VLV D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1M3 M7M5D1 D3 D7D5
ip is
Np : Ns
D4D2
Lm
iHV
D8D6 M8M6
(d) Mode IV (t3 − t4)
p
+
+
−
−−
−VLV D
D
s
ic
iL
D
A
B
C
c
+
+
VHV
VHVCHV
Ts Tx
N2 N1
M
N
s
Cc
Cf
VcM2 M4
M1M3 M7M5D1 D3 D7D5
ip is
Np : Ns
D4D2
Lm
iHV
D8D6 M8M6
(e) Mode V (t4 − t5)
Figure 5: Equivalent circuit for step-down conversion.
is still transferring power from VLV to VHV .It stops at t5 and a half switching cycle operation is com-pleted.
2.2. Step-Down Conversion
Interval 1: t0 ≤ t < t1. The equivalent circuit is shown inFigure 5(a). At t0, M5 and M8 are turned ON. The VHV isimmediately excited on the transformer and the whole volt-age is exerted on Leq. The transformer current increaseslinearly towards the load current at t1. M1 and M4 conductto transfer power.
Interval 2: t1 ≤ t < t2. The equivalent circuit is shownin Figure 5(b). At t1, M8 remains conducting while M5 isturned OFF. D6 conducts the freewheeling leakage current.
The transformer current reaches the load current level at t1.DC conducts the resonant Leq and the clamping capacitorCc.
Interval 3: t2 ≤ t < t3. The equivalent circuit is shown inFigure 5(c). At t2, with diode D6 conducting, M6 is turnedON with zero voltage switching.
Interval 4: t3 ≤ t < t4. The equivalent circuit is shown inFigure 5(d). At t3, M6 remains conducting while M8 is turnedOFF. The diode D7 starts to conduct the freewheeling leakagecurrent.
Interval 5: t4 ≤ t < t5. The equivalent circuit is shown inFigure 5(d). At t4, with D7 conducting, M7 is turned ONwith ZVS. Over this interval, the active switches change to
Figure 6: Simulation circuit and results. (a) Input voltage for boost mode. (b) Driving pulse for switches M1 and M2. (c) Output voltage forboost mode.
Figure 7: Simulation circuit and results. (a) Input voltage for buck mode. (b) Driving pulse for switches M1 and M2. (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 30×10−2
iL (A)
Passive RCDActive clampProposed flyback
(f)
Figure 8: Hardware layout and results. (a) Photograph of the prototype converter. (b) Switching pulse of switch, S1. (c) Transformer primaryside voltage. (d) Transformer secondary side voltage. (e) Converter with buck output. (f) Plot of efficiency in step-up mode.
the other pair of diagonal switches, and the voltage andthe transformer reverse its polarity. It stops at t5 and itcompletes a half switching cycle operation.
3. Simulation
The full-bridge DC-DC converter with flyback 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, switchingpulses are shown 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
100035 V
1 k
17
13 7
9
230 V
AC supply
PIC microcontrollerC8
D1
C5
D3
D2
D4
C9
C4
C7
C3
C6
C1
C2
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 Vin 15 (V)
Output voltage Vo 33 (V)
Switching frequency Fs 8 (kHz)
Filter capacitor C1 2200 (µF)
Flyback capacitor C2 100 (µF)
Main inductor L1 20 (µH)
Filter inductor L2 5 (µH)
The PIC 16F876S microcontroller can be used to generatethe driving pulse for MOSFET switches. Thus the PIC circuitacts as the control circuit.
4. Experimental Results
The input 230 V is stepped down to 15 V using a step-downtransformer and it is rectified to DC by the bridge rectifier.In boost mode, the output of the rectifier 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 ofrating 1 K, 10 W. The output of the flyback 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 30 V 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 efficiency of the bidirectional converter withvarious snubbers operated in the step-up mode.
It can be observed that the conversion efficiency 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
10 Advances in Power Electronics
pulses for the MOSFET switches. They are amplified usingthe driver IC IR2110. The gate signal is connected to port pinP1.0. Various steps involved in the firing 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 spike has beenalleviated by the flyback snubber. The flyback 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 efficiency.The simulation demonstrates the actual converter capabilityto alleviate voltage spikes and to improve the efficiency.
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,” IEEETransactions 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,” IEEE Transactions 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 flowmanagement,” 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 IEEE32nd 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.
