WWW.IJITECH.ORG
ISSN 2321-8665
Vol.03,Issue.04,
July-2015,
Pages:0566-0570
High-Conversion-Ratio Bidirectional DC-DC Converter with Ultra Capacitors
B. CHANDRASEKHAR1, K. SRAVANTHI2
1
PG Scholar, Vijaya Engineering College, Khammam, T.S, India.
Assistant Professor, Vijaya Engineering College, Khammam, T.S, India.
2
Abstract: In this paper, a high-conversion-ratio bidirectional
dc–dc converter with coupled inductor is proposed. In the
boost mode, two capacitors are parallel charged and series
discharged by the coupled inductor. Thus, high step-up
voltage gain can be achieved with an appropriate duty ratio.
The voltage stress on the main switch is reduced by a passive
clamp circuit. Therefore, the low resistance RDS(ON) of the
main switch can be adopted to reduce conduction loss. In the
buckmode, two capacitors are series charged and parallel
discharged by the coupled inductor. The bidirectional
converter can have high step-down gain. Aside from that, all
of the switches achieve zero voltage-switching turn-on, and
the switching loss can be improved. Due to two active clamp
circuits, the energy of the leakage inductor of the coupled
inductor is recycled. The efficiency can be further improved.
The operating principle and the steady-state analyses of the
voltage gain are discussed. Finally, a 24-V-input-voltage,
400-V-output-voltage, and 200-W-output-power prototype
circuit is implemented in the laboratory to verify the
performance.
on the previous research of the high step-up converter], a
high-efficiency, high-conversion-ratio, and clamp-mode
bidirectional converter is proposed. The initial high step-up
converter adds two pairs of additional capacitors and switches
on the secondary side of the coupled inductor to achieve an
HV ratio. The secondary side of the coupled inductor can
charge two capacitors in parallel and discharge in series when
the switch is on and off. Thus, the high output voltage is build
by replacing the diodes with switches. The high stepdown can
be also achieved because two capacitors are charged in series
and discharged in parallel.
II. INDUCTIVE COUPLING
In electrical engineering, two conductors are referred to as
mutual-inductively coupled or magnetically coupled when
they are configured such that change in current through one
wire induces a voltage across the ends of the other wire
through electromagnetic induction. The amount of inductive
coupling between two conductors is measured by their mutual
inductance. k is the coupling coefficient, Le1 and Le2 is the
Leakage inductance, M1 (M2) is the mutual inductance.
Keywords: RDS, DC-DC Converter, Ultra Capacitors.
I. INTRODUCTION
Renewable energy systems are more and more widely
used in the world such as solar and wind energy. However,
photovoltaic (PV) solar or wind power cannot provide
sufficient power when the load is suddenly increased. Thus,
the battery with bidirectional dc–dc converter is needed.
Conventionally, the batteries are series strings used to provide
a high voltage (HV). However, temperature differences or
little mismatches cause charge imbalance, which might
shorten the life of batteries. Although the batteries operated in
parallel strings alleviate the problems, the output voltage
remains low by this connection way Therefore, a highefficiency bidirectional dc–dc converter with a high
convention ratio is a key component of battery applications
Isolated bidirectional dc–dc converters such as half- and fullbridge types can provide high step-up and step-down voltage
gains by adjusting the turn ratio of the transformer. The high
step-up gain and the high step-down voltage gain can be
achieved. The number of switches is usually between four
and eight. Also, some isolated bidirectional converters are
characterized by a current-fed rectifier on the lowvoltage
(LV) side and a voltage-fed rectifier on the HV side. Based
Fig1. Inductive coupling between two conductors.
The coupling between two wires can be increased by
winding them into coils and placing them close together on a
common axis, so the magnetic field of one coil passes
through the other coil. The two coils may be physically
contained in a single unit, as in the primary and secondary
sides of a transformer, or may be separated. Coupling may be
intentional or unintentional. Unintentional coupling is called
cross-talk, and is a form of electromagnetic interference.
Inductive coupling favors low frequency energy sources.
High frequency energy sources generally use capacitive
coupling.
Copyright @ 2015 IJIT. All rights reserved.
B. CHANDRASEKHAR, K. SRAVANTHI
III. SWITCHED CAPACITOR
(8)
A. Introduction
Thus,
the
SC
behaves
like
a
resistor
whose
value
depends
on
A switched capacitor is an electronic circuit element used
capacitance
C
and
switching
frequency
f.
The
SC
resistor
is
for discrete time signal processing. It works by moving
S
used as a replacement for simple resistors in integrated
charges into and out of capacitors when switches are opened
circuits because it is easier to fabricate reliably with a wide
and closed. Usually, non-overlapping signals are used to
range of values. It also has the benefit that its value can be
control the switches, so that not all switches are closed
adjusted by changing the switching frequency (i.e., it is a
simultaneously. Filters implemented with these elements are
programmable resistance). See also: operational amplifier
termed "switched-capacitor filters," and depend only on the
ratios between capacitances. This makes them much more
applications.
This same circuit can be used in
suitable for use within integrated circuits, where accurately
discrete time systems (such as analog to digital converters) as
specified resistors and capacitors are not economical to
a track and hold circuit. During the appropriate clock phase,
construct.
the capacitor samples the analog voltage through switch one
and in the second phase presents this held sampled value to
B. The switched capacitor resistor
an electronic circuit for processing.
Fig2. Switched-capacitor resistor.
The simplest switched capacitor (SC) circuit is the switched
capacitor resistor, made of one capacitor C and two switches
S1 and S2 which connect the capacitor with a given frequency
alternately to the input and output of the SC. Each switching
cycle transfers a charge from the input to the output at the
switching frequency . Recall that the charge q on a
capacitor C with a voltage V between the plates is given by:
(1)
Where, V is the voltage across the capacitor. Therefore,
when S1 is closed while S2 is open, the charge stored in the
capacitor CS is:
(2)
When S2 is closed, some of that charge is transferred out of
the capacitor, after which the charge that remains in capacitor
CS is:
(3)
Thus, the charge moved out of the capacitor to the output
is:
(4)
Because this charge q is transferred at a rate f, the rate of
transfer of charge per unit time is:
(5)
Note that we use I, the symbol for electric current, for this
quantity. This is to demonstrate that a continuous transfer of
charge from one node to another is equivalent to a current.
Substituting for q in the above, we have:
(6)
Let V be the voltage across the SC from input to output. So:
(7)
So the equivalent resistance R (i.e., the voltage–current
relationship) is:
C. Ultra capacitor
A super capacitor (SC) (sometimes ultra capacitor),
formerly electric double-layer capacitor (EDLC)) is a highcapacity electro chemical capacitor with capacitance values
greater than 1,000 farads at 1.2 volt that bridge the gap
between electrolytic capacitors and rechargeable batteries.
They typically store 10 to 100 times more energy per unit
volume or mass than electrolytic capacitors, can accept and
deliver charge much faster than batteries, and tolerate many
more charge and discharge cycles than rechargeable batteries.
They are however 10 times larger than conventional batteries
for a given charge. Supercapacitors are used in applications
requiring many rapid charge/discharge cycles rather than long
term compact energy storage: within cars, buses, trains,
cranes and elevators, where they are used for regenerative
braking, short-term energy storage or burst-mode power
delivery. Smaller units are used as memory backup for static
random-access memory (SRAM). Super capacitors do not
have a conventional solid dielectric. They have electro
static double-layer capacitance or electro chemical pseudo
capacitance or a combination of both.
IV. OPERATING PRINCIPLE OF THE PROPOSED
CONVERTER
Fig.3 shows the circuit topology of the proposed
converter. This converter consists of the dc input voltage VL,
the power switch S1-S5, the clamp capacitor C1, two
blocking capacitors C2 and C3, and the coupled inductors Np
and Ns. The equivalent model of the coupled inductor
includes the magnetizing inductor Lm, the leakage inductor
Lk, and an ideal transformer. The switched-capacitor
technique in [31] and [32] has proposed that parallel-charged
and series-discharged capacitors can achieve high step-up
gain. Also, series-charged and parallel-discharged capacitors
can achieve high step-down gain. The character of the
coupled inductor is that the secondary side can have opposite
polarity when the switch is on and off. In the boost-state
operation, this character is combined with the switchedcapacitor technique. Two capacitors C2 and C3 are parallel
charged when the switch is on and series discharged when the
switch is off. In the buck-state operation, the coupled inductor
is used as a transformer. Thus, two capacitors C2 and C3 can
be series charged by HV side and parallel discharged through
the secondary side. In addition, the problem of the energy of
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0566-0570
High-Conversion-Ratio Bidirectional DC-DC Converter with Ultra Capacitors
the leakage inductor is also solved. In the boost-state
operation, S1 is the main switch, and capacitor C1 recycles
the energy.
Fig3. Circuit configuration of the bidirectional converter.
The voltage across switch S1 can be clamped. Since
switch S1 has an LV level, the low conducting resistance
RDS(ON) of the switch is used to reduce the conduction loss.
In the buck-state operation, the main switches are S2 and S5.
Two capacitors C2 and C3 with switches S3 and S4 are used
as active clamp circuits, recycling the energy of the leakage
inductor on the secondary side of the coupled inductor.
Capacitor C1 with switch S2 is another active clamp circuit
that recycled the energy of the leakage inductor on the
primary side. Thus, four switches are ZVS turned on. The
switching loss is improved; the efficiency can be increased. It
is because that the high step-up converter needs a large input
current, which results that the conduction loss is larger than
the switching loss. Thus, reducing the switch voltage stress
for alleviating the conduction loss and the elimination of
reverse-recovery current is the key point to improve
efficiency. Similarly, the main switch of the high step-up and
step-down converters suffers HV stress and low conducting
current. The switching loss should be reduced to improve
efficiency To simplify the circuit analysis, the following
conditions are assumed.
Fig5. Experiment results in the Boost mode 40w.
V. SIMULATION RESULT
Fig4. Simulation model DC-DC Converter with Coupled
Inductor.
Fig6. Experiment results in the Boost 200 watts.
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0566-0570
B. CHANDRASEKHAR, K. SRAVANTHI
Fig7. Experiment results in theBuck mode 40 watts.
Fig9. Experiment results in the Buck mode 40watts ultra.
Fig10. Simulate model DC-DC Converter with Ultra
capacitors.
VI. CONCLUSION
This paper has proposed a novel, high-efficiency, and high
step-up/step-down bidirectional dc–dc converter. By using
the capacitor charged in parallel and discharged in series by
the coupled inductor, high conversion ratio and high
efficiency have been achieved. The steady-state analyses of
the proposed converter have been discussed in detail. The
voltage gain and the utility rate of the magnetic core have
Fig8. Experiment results in the Buck mode 200watts.
International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0566-0570
High-Conversion-Ratio Bidirectional DC-DC Converter with Ultra Capacitors
been increased by using a coupled inductor with a low turn
Author’s Profile:
ratio. The energy of the leakage inductor has been recycled
B.Chandrasekhar, received B.Tech
with the clamp circuit. A prototype circuit has been built in
degree in Electrical and Electronics
the laboratory. Experimental results show that the maximum
Engineering from Srirajarajeswari
efficiency is 97.33% at the boost mode and 96.23% at buck
Engineering
College,
Karepally,
mode. This topology provides efficient conversion of various
Khammam, T.S. And currently pursuing
power sources. This technique can be also applied in different
M.Tech in Power Electronics at Vijaya
power conversion systems easily.
Engineering College, Khammam,T.S.
My areas of interest are Power Systems, and Power
Electronics, Electrical Machines.
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International Journal of Innovative Technologies
Volume.03, Issue No.04, July-2015, Pages: 0566-0570