International Journal of Emerging
Technology & Research
Volume 1, Issue 4, May-June, 2014
(www.ijetr.org)
ISSN (E): 2347-5900 ISSN (P): 2347-6079
Single Switch Isolated High Step Up Dc-Dc Converter
Sharmini.J.R1, Shibi.A.S2, Santhia.V.S3
1, 2, 3
PG Student, Department of Electrical and Electronics Engineering, Loyola Institute Of Technology, Chennai
Abstract- In this paper single switch isolated DCDC converter is designed and developed for
voltage regulation. Desired features of the
proposed DC-DC converter has the advantage of
using less number of switches than other existing
isolated DC-DC converter. The operating
principle and parameter design of the converter
are described in the paper. This paper presents a
single switch isolated converter require high
voltage regulation ratios, the isolated topologies
are ideal, because they can achieve high efficiency
than non isolated converters. Simulation of
proposed converter is done and results obtained
are satisfactory.
Index Terms- Isolated dc-dc converter, high step-up, high
voltage gain, high efficiency.
I. INTRODUCTION
The renewable energy sources such as PV modules,
fuel cells or energy storage devices such as capacitors
or batteries deliver output voltage. This project
presents an isolated converters are desirable in the
dc-dc power conversion applications. In order to
connect them to the grid the voltage level should be
adjusted according to the electrical network standards
in the countries. First of all the voltage should be
stepped up to sufficient level at which the DC/DC
conversion can be performed. The proposed DC-DC
converter has the advantage of using less number of
switches than other existing isolated DC-DC
converter and therefore a low cost. To obtain high
step up voltage gain, the output voltage lift is adopted
[1]. Consequently, a transformer with a low turn’s
ratio can be applied, which makes the transformer
design and optimize easily. The characteristics of the
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output voltage lift are similar to the forward
converter in the charging mode and the fly back
converter in the discharging mode.
Many topologies have been proposed for DC-DC
converters, which in general can be classified into
two categories: isolated topologies and nonisolated
topologies [3]. Nonisolated converters, such as boost
converter and quasi-double boost converter [4], have
been used for PV systems. These topologies are
commonly used in the applications where the voltage
step-up regulation ratio is low (usually less than 4)
and usually have higher efficiency than the isolated
topologies because no galvanic transformers
are
used. However, in the applications that require high
voltage regulation ratios, the isolated topologies are
ideal candidates, because they can achieve higher
efficiency than nonisolated converters by properly
designing the transformer’s turn ratio to get the
optimal duty cycle. Moreover, an isolated converter
provides isolation between input and output, which is
desired from safety perspective.
This paper proposes a single-switch isolated DC-DC
converter, which has less number of switches than
any existing isolated topologies and, therefore, a
lower cost. The number of switches of the proposed
converter is the same as that of a forward or flyback
converter. However, compared to the forward or
flyback topology, the energy in the proposed
topology is transferred in a whole switching period
instead of in the switch-on or switch-off time interval
only, which not only decreases the peak current but
also increases the efficiency of the converter.
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International Journal of Emerging Technology & Research
Volume 1, Issue 4, May-June, 2014
(www.ijetr.org) ISSN (E): 2347-5900 ISSN (P): 2347-6079
II. BLOCK DIAGRAM OF NEW
TOPOLOGY
Block diagram for the proposed converter is shown in
Fig 1.
Figure 1. Block diagram of new topology
Pulses to the switch are given by using PWM control
technique. Input and output filter used to eliminate
harmonics and ripple at the input and output side.
Rectifier converts given DC input to the
corresponding DC voltage. DC-DC converter is a
normal fly-back and forward converter. It has single
switch with high frequency transformer. The
proposed converter is applied for voltage regulation.
In order to meet the safety standards of galvanic
isolation, some isolated converters for high-step-up
applications have been proposed.
III. NEW CONVERTER TOPOLOGY
The circuit diagram of the proposed single-switch
isolated DC-DC converter is shown in Fig. 2, which
consists of allow-voltage-side (LVS) circuit and a
high-voltage-side (HVS) circuit connected by a highfrequency (HF) transformer.
The extremely-high enhancement gain is also
separated by the attenuated boost conversion of
forward converter and flyback converter, thus the
device stress is reduced and the power efficiency is
improved. The primary has a PWM switching
voltages occurred by single main switch. The
secondary is a structure where the forward converter
and the flyback converter are separated by
transformer winding.
IV. CIRCUIT OPERATION
The converter has 4 modes of operation.
A.Mode1
Current flows to the magnetizing inductance and the
primary winding (Np) as a result of turning on switch
(Q). The primary current is transferred to the
secondary (Nfw) coil of the forward converter. Then,
the AC power is rectified into DC which load
requires through forward diode (Dfw). Since flyback
diode (Dfb) is reverse-biased, the output capacitor
provides the load current during this mode.
The circuit diagram of new converter topology is
shown in Fig 2.This converter operates with high
efficiency high-step-up isolated dc–dc converter
using one control gate driver signal.
Figure 3.Mode1
Figure 2. Basic circuit of proposed topology
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International Journal of Emerging Technology & Research
Volume 1, Issue 4, May-June, 2014
(www.ijetr.org) ISSN (E): 2347-5900 ISSN (P): 2347-6079
B.Mode2
D.Mode 4
When switch (Q) is turned off, forward diode (Dfw)
is reverse-biased and the energy stored in L out is
transferred to the load by the freewheeling current via
Dff and at the same time, the energy magnetically
stored at Lm is also supplied to load through Dfb of
the flyback converter. Thus, all the freewheeling
current in magnetic devices decreases linearly.
The transformer of the forward-flyback converter is
de-magnetized completely during this period and the
output voltage is maintained by the discharge of the
output capacitors. All the rectifier diodes are reversebiased.
Figure 6.Mode4
V. SIMULATION STUDIES
Figure 4.Mode2
C.Mode3
The forward converter starts to operate when all the
energy in Lout is discharged, and then freewheeling
diode (Dff) is reverse-biased. The energy only stored
in L is supplied to load through the flyback converter.
On the basis of obtained design, simulation of
converter carried out in DCM operation. Fig 6.
Shows the simulation model of proposed converter in
DCM operation. It mainly consists of filter,
transformer with three winding and battery which is
placed in primary side of the converter. The converter
consists of PWM control using voltage follower
method.
The energy transfer is controlled by switching
operation of MOSFET Q1. Pulses to the switch are
given by voltage follower method.
Voltage follower approach is applied for the PWM
control of the converter, which needs output voltage
sensing. Output voltage regulation is provided by the
feedback loop shown in Fig 8.
Figure 5.Mode3
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International Journal of Emerging Technology & Research
Volume 1, Issue 4, May-June, 2014
(www.ijetr.org) ISSN (E): 2347-5900 ISSN (P): 2347-6079
Figure 9. Switching pulse
Figure 7.Simulation diagram
TABLE I
CIRCUIT SPECIFICATIONS FOR PROPOSED CONVERTER
Figure 8.PWM control
From the Fig 8, output voltage (Vo) is compared with
a reference voltage (Vref) and error is amplified and
given to a proportional integral (PI) controller which
in turn compared with saw tooth ramp, thus providing
pulses to power switch. Output waveform for the
control circuit is shown in Fig 8. A pulse to the
switch is shown in Fig 9.
The primary has a PWM switching voltages occurred
by single main switch. The secondary is a structure
where the forward converter and the flyback
converter are separated by transformer winding.
However, the outputs are serially connected for the
output voltage boost. Forward-flyback converters
deliver the required energy to the load when the main
switch turns on or off, holding an advantage in terms
of supplying more power to the load than any other
single-ended isolation schemes. The SFFB converter
has single-ended scheme, which contributes to the
cost competiveness in industry market .Technically,
the proposed converter has a reduced voltage rating
of rectifying diodes by separating secondary winding.
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Input Voltage ,Vin
30V
Output Voltage, Vo
400V
Output Power, Po
160W
Input filter inductance Lin
0.27µH
Output Capacitor C0
220µF
VI. RESULTS AND DISCUSSIONS
The simulated input and output voltage waveforms
are shown in Fig 10 and Fig 11. From the below
results, 400V output voltage obtained for 30V input.
An isolated converter is developed with 400V output
voltage having transformer isolation with 50 kHz
switching frequency. This converter can achieve
efficiency 98% with sufficient suppression of ripple
at the outside side. The primary has a PWM
switching voltages occurred by single main switch. In
addition, input to output isolation may be required to
meet safety standards.
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International Journal of Emerging Technology & Research
Volume 1, Issue 4, May-June, 2014
(www.ijetr.org) ISSN (E): 2347-5900 ISSN (P): 2347-6079
converter can be easily applied for other types of
renewable energy sources, such as wind turbine
generator, as well.
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Figure 10.Input waveform
Figure 11.Output waveform
VII. CONCLUSION
This paper has proposed a single-switch isolated DCDC converter for voltage regulation. Compared to
traditional half-bridge or full-bridge isolated
converter, the number of switches of the proposed
converter has been reduced. Compared to the forward
converter with the same transformer, the proposed
converter has advantages of higher voltage regulation
ratio. Simulation studies have been performed in
MATLAB. Simulation results have validated the
theoretical analysis of the proposed converter and
have demonstrated that the proposed converter
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power switch. Experimental results have further
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International Journal of Emerging Technology & Research
Volume 1, Issue 4, May-June, 2014
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(www.ijetr.org) ISSN (E): 2347-5900 ISSN (P): 2347-6079
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