International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
Soft Switching Sepic Boost Converter with High
Voltage Gain
Reshma K R
Renjini G
PG Scholar
Dept. of Electrical and Electronics
Jyothi Engineering College, Cheruthuruthy
Thrissur, India
reshmajec@gmail.com
Assistant Professor
Dept. of Electrical and Electronics
Jyothi Engineering College, Cheruthuruthy
Thrissur, Kerala
renjini@jecc.ac.in
Abstract— The paper presents a high gain dc-dc converter
which is derived from a traditional SEPIC (single-ended
primary-inductor) converter. The distributed generation based
system with renewable energy resources have rapidly developed
in recent years. These distributed generation systems are
powered by sources such as fuel cell, photovoltaic (PV) systems
and batteries. This consists of two conversion stages, in the first
stage the low level voltage from the PV cell is converted to high
level voltage by using a dc-dc converter. In the second stage the
high level dc voltage is converted into AC voltage by using
inverter. The electrical energy demand requirements can be
achieved by increasing the gain of the converter. The proposed
converter high gain achieved by replacing the coupled inductor
instead of inductor in the basic sepic converter. Further increase
of gain is achieved by using charge pump capacitor cell. The
main advantage of the sepic converter is continuous input
current, which can be helpful in accurate PowerPoint tracking of
solar cell The inductorless regenerative snubber that reduces
switching losses and helps to attain soft switching (zero voltage
and zero current switching) conditions.
Keywords— sepic conveter, pv cell, coupled inductor, charge
pump capacitor cell, snubber .
I. INTRODUCTION
In recent year the energy scarcity and atmospheric
pollution that led to more researches on the renewable energy
sources such as the Photovoltaic cells and fuel cells. The
renewable energy systems generate low voltage output,
therefore high step-up dc /dc converters are widely used in
many renewable energy applications. Among renewable
energy systems, photovoltaic systems are important role in
future energy production. Such systems that produces
electrical energy from light energy, and convert low level
voltage into high level voltage via a step-up converter, which
can convert energy into electricity using a grid-by-grid
inverter [1]. Classical isolated boost converters like flyback
or current-fed push-pull converters are easily achieve high
voltage gain. But the main drawback of these isolated dc-dc
converters are large size , the energy of the transformer
leakage inductance can produce high switching stress,
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
increasing switching losses, and large electro-magnetic
interference. Therefore non-isolated converter topologies are
widely used in many applications.
The conventional boost converters such as boost, buckboost, cuk, sepic and zeta converters can be used for this
purpose, but to attain high voltage gain the duty cycle of the
converter must be very high i.e around 0.9. This is not
possible due to the reverse recovery problem of the diode. The
diode reverse recovery current can reduce the efficiency of the
converter when it’s operating with high current voltage levels.
Many topologies has been proposed to overcome this
drawbacks. In classical non-isolated dc-dc converter voltage
multiplier technique is applied in order to get high step-up
gain or high voltage gain [3]. The basic structure of the single
phase voltage multiplier cell is composed of capacitors, diodes
and a resonant inductor. The voltage multiplier cell also
operates without the resonant inductor. It is possible to add
more multiplier cells in order to achieve high voltage gain.
The voltage multiplier cell increases the static gain of the
classical boost converter by a factor of (M+1). Where M is the
number of multiplier cells. The main drawback of this
technique is usage of large number of components that
increases the conduction losses.
Switched capacitor and switched inductor structures
introduced for obtaining transformerless hybrid dc-dc PWM
converters [4]. These switched inductor and capacitor
structures are introduced in classical converters which can
provide steep conversion ratio. When the active switch of the
converter is on, capacitors in the capacitor switching blocks
are discharged in series or the inductors in the inductor
switching blocks are charged in parallel. When switch is
turned off, capacitors in C–switching blocks are charged
parallel or the inductor in the L-switching blocks are
discharged series . Main disadvantages of this technique is
usage of large number of components, cost and control
complexity.
Voltage lift technique has been proposed in sepic
converters [5]. Voltage lift technique is different from
switched capacitor and switched inductor techniques. Both
inductors and capacitors plays important role in voltage lift
technique. The main advantages of this converter compared to
other converters are small ripple and high efficiency in simple
structures.
The cascade boost converter is derived from the basic
boost converter by adding the parts inductor ,diode and
capacitors (L–D–C). In this topology, the output voltage the
converter increase in a simple geometric progression. Main
disadvantage is high conduction loss therefore overall
converter efficiency decreases[6].
The new trend for increasing voltage gain in boost
converter is use of coupled inductor/tapped inductor [7]. High
voltage gain is achieved by adjusting the turns ratio of the
coupled inductor. The benefits of using coupled inductor are
First, it helps to reduce the input ripple and second, it makes
the total inductor size low because of using only one bobbin
and core. But the converter efficiency is degraded due to the
losses with the leakage inductance.
Single phase improved active clamp coupled inductor
based converter is proposed [9]. In this converter, the active
clamp circuit is used instead of passive lossless clamp circuit.
Therefore both main and auxiliary switches are turned on at
zero voltage switching. The turn off losses of the two switches
are reduced greatly due to parallel capacitors. The main
disadvantage is the voltage stress of the output diode is higher
than its output voltage . In [11], different types of high gain
sepic converters with tapped inductor are proposed. Sepic
converter is a dc-dc converter. The sepic converter is a boost
converter followed by a buck-boost converter. The main
feature of the sepic converter is output has the same voltage
polarity as the input. The circuit diagram of the basic sepic
converter shown in fig 1.
Fig 1: circuit configuration of basic sepic converter
Coupled inductor or tapped inductor inserted in basic sepic
converter to achieve high gain i.e L1 of the basic sepic
converter is replaced by a coupled inductor or tapped inductor
shown in fig 2. Therefore gain of the sepic converter is
increased by increasing the turns ratio of the coupled inductor.
Fig 2: Sepic converter with coupled inductor
Sepic converter with coupled inductor scheme for
maximum power point tracking is proposed. In PV cells, the
periodically shift the operating point with pulsating input
current. Therefore, maximum power point (MPP) tracking is
difficult. The main feature of this converter is that pulsating
current of the coupled inductor does not flow at the input port.
Due to this inherent property of sepic converter they are
mostly used in photovoltaic applications. The main feature of
the converter compared to the classical converter are low array
current ripple, load voltage has the same polarity as that of
supply voltage, low amplitude of SCA current ripple that
reduces EMI. The main drawback is it requires additional
inductor and capacitor compared to that of classical
converter[12].
High gain boost dc-dc converter is proposed for microgrid
[13]. In this converter, the capacitors charges in parallel and
discharges in series manner with the coupled inductor in order
to achieve high voltage gain. The converter has low
conduction losses but the leakage inductance in the coupled
inductor is high that causes power losses and high voltage
spikes. Therefore clamp circuit is required for recycle the
leakage energy of the coupled inductor.
Sepic converter with reduced voltage stress is proposed
[14]. In this converter splitting of the secondary winding of the
coupled inductor into two windings that reduces the voltage
stresses on the switches and diodes. The voltage stress on the
diodes and switches is less than that of the output voltage and
soft switching can be achieved.
High gain non-isolated boost converter integrated with
sepic converter topology introduced in [15]. In this topology,
the classical sepic converter combines with the isolated
converter. The converter provides additional gain with the
help of the isolated converter. The main advantages of the
converter are high boosting capability and distributed voltage
stress.
RCD clamp circuits are used to limit the voltage spikes,
which is caused by the primary leakage inductance[16]. The
proposed clamp circuit improves the efficiency of the flyback
converter. Different regenerative snubber circuit are proposed
for isolated converters. RCD snubber, Zener diode snubber
and non-dissipative LCD snubber are different types of
snubber circuits. In RCD snubber, which allows the
discharging of leakage energy of the coupled inductor to the
snubber capacitor and then the trapped or captured energy in
the snubber capacitor is dissipated through the snubber
resistor. The main advantage of Zener diode over the RCD
snubber is that the voltage stress across the switch is
independent of duty cycle or load. But in the lossless LCD
snubber, when switch is turned off the primary leakage energy
is trapped in the snubber capacitor. As the switch is turned on
the trapped energy is partially forward to the output side and
partially feedback to the supply side.
Conventional pulse width modulation control technique
has slow dynamic response. One-cycle control is the other
modulation control technique. The one cycle control
technique that overcomes inherent drawback of pulse width
modulation control technique and achieves fast dynamic
response. In PWM control, a large number of switching cycles
is required to reach steady-state condition. One-cycle control
(OCC) is a nonlinear control method and it takes only one
cycle for the average value of the switched variable to reach a
new steady-state after a transient. This provides fast dynamic
response, excellent power source disturbance rejection, robust
performance, and automatic switching error correction. Here
one cycle control method is used adopted.
This paper is organized as follows. Section II and III
describes high gain sepic boost converter and its operation.
MATLAB simulation along with results is explained in
Section IV and conclusion is stated in Section V.
II.
HIGH GAIN SEPIC CONVERTER
The paper introduces a high gain dc-dc sepic boost
converter for renewable energy system applications. The
circuit configuration of high gain sepic converter shown in
fig.3. The high gain sepic converter consist of coupled
inductor, charge pump capacitor cell, buffer capacitor C1,
regenerative snubber, output capacitor Co and load resistor RL.
The charge pump capacitor cell comprised of capacitor C2 and
diodes D1 and Do. The regenerative snubber consists of
snubber capacitor CS and snubber diodes Ds1 and Ds2.The
regenerative snubber can provide zero-voltage and zerocurrent switching and recycles the captured leakage energy
from the primary winding of the coupled inductor to the
capacitor C2, which increases the overall efficiency of the
converter.
snubber capacitor voltage Vcs drops to zero, Ds1 starts to
conduct and snubber capacitor clamps to zero voltage level.
When the charge pump capacitor attain fully charged
condition and the secondary inductor current decays to zero,
the snubber diodes Ds1 and Ds2 cut off at zero current. During
this instant the input inductor and magnetizing inductance of
coupled inductor keeps charging. When the switch is turned
off, at this instant voltage across the snubber capacitor (Vcs) is
zero. Therefore zero voltage switching is achieved. During
this interval snubber capacitor keeps charging and at the same
time secondary leakage inductor current builds up through the
charge pump capacitor C2 and output diode D0. When voltage
across the snubber capacitor reaches its peak voltage, then the
snubber diode Ds1 cut off and both input inductor and
magnetizing inductance of coupled inductor discharges to the
output. Therefore the output voltage equals to the sum of
charge pump capacitor voltage, buffer capacitor voltage and
(1+n) times of the magnetizing inductance voltage.
IV.
SIMULATION RESULTS
The simulation of high gain sepic boost converter with
charge pump capacitor and coupled inductor has been carried
out by using MATLAB software. An supply voltage of 35V
and switching frequency of 60000 Hz is chosen and an output
voltage 380V is obtained. The duty ratio is equal to 0.54 and
the circuit parameters are listed in Table I. Fig 4 shows the
simulation waveforms of the high gain sepic converter (a) the
supply voltage, output voltage and output current waveforms.
(b) Voltage and current across the switch. Zero voltage and
zero current switching is achieved. (c) Input inductor current,
primary and secondary current of the coupled inductor. (d)
Output diode voltage and current waveform. Fig 5, fig 6
shows the waveform of line and load regulation respectively.
TABLE I.
SIMULATION PARAMETERS
Parameters
Fig .3: circuit diagram of the high gain sepic converter.
III.
OPERATION OF THE CONVERTER
The switch is turned ON, the voltage Vin is applied
across the input inductor Lin .Therefore the input inductor
current starts ramping up at the same time the secondary
leakage inductance keeps discharging through the output diode
Do to the output. The secondary leakage inductor current
decays to zero and the diode Do has entered cut off. Therefore
snubber diode Ds2 starts conduct and allows the snubber
capacitor to resonant with the secondary leakage inductance
L2k. Therefore the captured energy in the snubber capacitor is
transferred into charge pump capacitor C2. During this time
interval secondary inductor current iL2 reverses. When the
value
Input voltage Vs
35V
Output voltage Vo
380V
Output power Po
200W
Switching frequency fs
60kHz
Turns ratio N1:N2
16:64
Magnetizing inductance
180µH
Output filter capacitor Co
1.25 F
Charge pump capacitor C2
1.253 F
buffer capacitor C1
20.05 F
Snubber capacitor
7.69nF
in p u t c u rre n t
10
8
6
0.025
0.025
0.025
0.025
0.025
0.0251
0.0251
0.0251
0.0251
0.0251
0.025
0.025
0.025
0.025
0.025
0.0251
0.0251
0.0251
0.0251
0.0251
0.025
0.025
0.025
0.025
0.025
Time
0.0251
0.0251
0.0251
0.0251
0.0251
10
iL 1
0
-10
-20
5
iL 2
0
-5
(c)
Fig 4: Simulink model of the converter
1.5
g a te p u ls e
1
0.5
36
0
in p u t v o lta g e
-0.5
0.025
0.025
0.025
0.025
0.025
0.0251
0.0251
0.0251
0.0251
0.0251
0.025
0.025
0.025
0.025
0.025
0.0251
0.0251
0.0251
0.0251
0.0251
0.025
0.025
0.025
0.025
0.025
Time
0.0251
0.0251
0.0251
0.0251
0.0251
35
0
0
0.005
0.01
0.015
0.02
0.025
0.03
VD0
34
-200
o u tp u t v o lta g e
-400
o u tp u t c u rr e n t
500
0
0
0.005
0.01
0.015
0.02
0.025
0.03
iL 0
10
0
-10
1
0.5
0
(d)
0
0.005
0.01
0.015
Time
0.02
0.025
0.03
(a)
Fig 4: simulation results: (a) supply voltage and output voltage, output
current, (b) switch voltage Vds and switch current ids, (c) input inductor
current ilin, primary and secondary currents of coupled inductor iL1 and iL2, (d)
output diode voltage VDo and output diode current iDo
1.5
600
O u t p u t V o lta g e
g a te p u l s e
1
0.5
0
-0.5
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.0251
400
200
0
-200
0
0.002
0.004
0.006
0.008
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.01
0.012
0.014
0.016
0.018
0.02
250
36
V d s , id s
200
In p u t V o lt a g e
150
34
100
32
50
0
0.025
0.025
0.025
0.025
0.025
Time
0.025
0.025
0.0251
30
Time
(b)
Fig5: Line regulation of the converter
L o a d C u rre n t
0.8
0.6
0.4
0.2
0
-0.2
0
0.002
0.004
0.006
0.008
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.01
0.012
0.014
0.016
0.018
0.02
O u tp u t V o lta g e
600
400
200
0
-200
Time
Fig 6: load regulation of the converter
V.
CONCLUSION
The paper introduces high gain sepic boost converter with
one cycle control technique. High gain is attained by using
charge pump capacitor cell and coupled inductor without the
use of extreme value of duty cycle (D). Inductorless passive
regenerative snubber helps the converter to achieve zerovoltage and zero-current switching, which increases the
converter efficiency. The validity of the converter is tested by
using the MATLAB software and obtained the required output
waveforms.
References
[1]
M. Karimi-Ghartemani, S. A. Khajehoddin, P. Jain, and A. Bakhshai, “A
systematic approach to DC-bus control design in single-phase gridconnected renewable converters,” IEEE Trans. Power Electron., vol. 28,
no. 7, pp. 3158–3166, Jul. 2013.
[2] S.-M. Chen, T.-J. Liang, and K.-R. Hu, “Design, analysis, and
implemen- tation of solar power optimizer for DC distribution system,”
IEEE Trans. Power Electron., vol. 28, no. 4, pp. 1764–1772, Apr. 2013.
[3] M. Prudente, L. L. Pfitscher, G. Emmendoerfer, E. F. Romaneli, and R.
Gules, “Voltage multiplier cells applied to non-isolated DC–DC
converters,” IEEE Trans. Power Electron., vol. 23, no. 2, pp. 871–887,
Mar. 2008.
[4] B. Axelrod, B. Yefim, and A Ioinovici, “Switched-capacitor/switchedinductor structures for getting transformerless hybrid DC-DC PWM
converters,” IEEE Trans. Circuit Syst., vol. 55, no. 2, pp. 687–696, Mar.
2008.
[5] M. Zhu and F. L. Luo, “Series SEPIC implementing voltage-lift
technique for DC–DC power conversion,” IET Power Electron., vol. 1,
no. 1, pp. 109–121, Mar. 2008.
[6] F. L. Luo and H. Ye, “Positive output cascade boost converters,” IEE
Proc. Electr. Power Appl., vol. 151, no. 5, pp. 590–606, Sep. 2004.
[7] N. Vazquez, L. Estrada, C. Hernandez, and E. Rodriguez, “The tappedinductor boost converter,” in Proc. IEEE Int. Symp. Ind. Electron., Jun.
2007, pp. 538–543.
[8] R.-J.WaiandR.-Y.Duan,“High step-up converter with coupled-inductor,”
IEEE Trans. Power Electron., vol. 20, no. 5, pp. 1025–1035, Sep. 2005.
[9] Y. Zhao, W. Li, and X. He, “Single-phase improve active clamp
coupled- inductor-based converter with extended voltage doubler cell,”
IEEE Trans. Power Electron., vol. 27, no. 6, pp. 2869–2878, Jun. 2012.
[10] Jeff Falin “Designing DC/DC converters based on SEPIC topology”.
[11] A. Abramovitz, J. Yao, and K. Smedley, “Derivation of a family of high
step-up tapped inductor SEPIC converters,” Electron. Lett., vol. 50, pp.
1626–1628, Nov. 2014.
[12] M. Veerachary, “Power tracking for nonlinear PV sources with coupled
inductor SEPIC converter,” IEEE Trans. Aerosp. Electron. Syst., vol. 41,
no. 3, pp. 1019–1029, Jul. 2005.
[13] Y. Hsieh, J. Chen, T. Liang, and L. S. Yang, “A novel high step-up DCDC converter for a microgrid system,” IEEE Trans. Power Electron.,
vol. 26, no. 4, pp. 1127–1136, Apr. 2011.
[14] B. Axelrod and Y. Berkovich, “New coupled-inductor SEPIC converter
with very high conversion ratio and reduced voltage stress on the
switches,” in Proc. IEEE 33rd Telecommun. Energy Conf., Oct. 2011,
pp. 1–7.
[15] K.B.Park, G.W.Moon, and M.J.Youn,“Non isolated high step-up boost
converter integrated with SEPIC converter,” IEEE Trans. Power
Electron., vol. 25, no. 9, pp. 2266–2275, Sep. 2010.
[16] A.Hren,J.Korelic,and M.Milanovic,“RC-RCD clamp circuit for ringing
losses reduction in a flyback converter,” IEEE Trans. Circuits Syst. II,
Exp. Briefs, vol. 53, no. 5, pp. 369–373, May 2006.