Download design and analysis of interleaved boost converter for photovoltaic

International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
DESIGN AND ANALYSIS OF INTERLEAVED BOOST
CONVERTER FOR PHOTOVOLTAIC MODULE
K.E.Lakshmi Prabha1, Thangapandian.R2
Assistant Professor1, PG Student2
Karpaga Vinayaga College of Engineering and Technology1, 2
[email protected], [email protected]
of energy used on Earth originate from the sun’s
energy.
Abstract- Solar energy is derived from solar
radiations that are replaced constantly. An
appropriate DC-DC converter is suggested for very
effective solar energy systems. Interleaved Boost
Converter (IBC) concept is used in this paper for
photovoltaic module applications. The advantages of
interleaved boost converter related to the
conventional boost converter are low input current
ripple, high efficiency, faster transient response,
reduced electromagnetic emission and improved
reliability. This paper focuses on a two-phase IBC's
with (i) the front end inductors magnetically coupled
(ii) uncoupled inductors and (iii) inversely coupled
inductors performance have been analyzed and
related for three types of IBC. Based on the output
voltage ripple, input current ripple and inductor
current ripple of the three types of converters are
compared. The waveforms of input, inductor
current ripple and output voltage ripple are
achieved using MATLAB/Simulink. From the
simulation results, the best of the three types of IBC
is concluded.
Solar energy is considered one of the most promising
energy sources due to its infinite power. Thus modern
solar technologies have been penetrating the market at
faster rates. The solar technology that has the greatest
impact on our lives is photovoltaic. Not in terms of the
amount of electricity it produces, but because of the fact
that photovoltaic cells – work silently, not polluting –
can generate electricity wherever sun shines, even in
places where no other form of electricity can be
obtained. The word Photovoltaic is a combination of
the Greek word for light and the name of the physicist
AlessandroVolta It detect the direct conversion of
sunlight into electricity by means of solar cells. The
proper converter is designed for photovoltaic module
applications.
The Interleaved boost converter has high voltage step
up, reduced output voltage ripple, low switching loss,
faster transient response. Also, the steady-state voltage
ripples at the output capacitors of IBC are reduced.
Although IBC topology has more inductors increasing
the complexity of the converter correlated to the
classical boost converter it is chosen because of the low
ripple content in the input and output sides. In order to
decrease this complexity, this paper considers the aids
of coupled, uncoupled and inversely inductors for IBC.
Complete analysis has been done to study the ripple
content of all the three types of the converter. The
proper IBC for photovoltaic module application is
suggested. Switching pulses are generated using pulse
generator.
Keywords: DC-DC Converter, Uncoupled, Directly
coupled, inversely coupled, ripple.
I. INTRODUCTION
For many years, fossil fuel has been the primary
source of energy. However, there is a limited supply of
these fuels on Earth and they are being used much more
rapidly than they are being created. Eventually, they
will run out. In addition, because of safety concerns and
waste disposal problems, renewable energy is definitely
the solution since such technology is “clean” or “green”
because they produce few if any, pollutants. The world
trend nowadays is to find a non-depletable and clean
source of energy. The most effective and harmless
energy source is probably solar energy, which for many
applications is so technically straightforward to use.
With the exception of nuclear and geothermal, all forms
II. BLOCK DIAGRAM
The block diagram representation of proposed
system is shown in figure1.
34
International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
lead to overheating of shaded cells. Solar cells become
less efficient at higher temperatures and installers try to
provide good ventilation behind solar panels.
Photovoltaic Array
The power that one module can produce is not
sufficient to meet the requirements of home or business.
Most PV arrays use an inverter to convert the DC
power into alternating current that can power the
motors, loads, lights etc. The modules in a PV array are
usually first connected in series to obtain the desired
voltages; the individual modules are then connected in
parallel to allow the system to produce more current.
Fig. 1 Block Diagram Representation of Proposed
System
B. Interleaved Boost Converter
Interleaved boost converter has been studied in
recent years with the goal of improving power
converter performance in terms of efficiency, size,
conducted electromagnetic emission, and transient
response. The benefits of interleaving include high
power capability, modularity, and improved reliability.
Interleaving add benefits such as reduced ripple current
in both input and output circuits. Higher efficiency is
realized by splitting the output current into ‘n’ paths,
substantially reducing I2R losses and inductor losses. In
addition, interleaving is also employed to reduce the
input current ripple, and therefore to minimize the size
of the input filter that would be relatively large if a
single boost converter was used.
In this proposed system, the sunlight is
incident on the solar panel or module, and then the dc
voltage is produced. This voltage is fed into the
interleaved boost converter for step up the dc voltage.
For e.g. 12V to 70V. The Controller is used for
generating the control signals to turn on/off of the
power switches present in the converter circuit to get
the desired output voltage. The output voltage of the
DC-DC converter is given to the filter circuit for
regulating the dc voltage. This regulated dc output is
given to the dc load. This proposed system consists of
following components. They are Photovoltaic module,
Interleaved Boost Converter, Controller, DC filter, DC
load.
A. Photovoltaic Arrangement
C. Controller
In this system, micro controller is used for
generating the control signal depends upon the
applications. This control signals are used to turn on/off
of the power switches present in the converter circuit to
get the desired output voltage.
Photovoltaic Cell
PV cells are made of semiconductor materials,
such as silicon. For solar cells, a thin semiconductor
wafer is specially treated to form an electric field,
positive on one side and negative on the other. When
light energy strikes the solar cell, electrons are knocked
loose from the atoms in the semiconductor material. If
electrical conductors are attached to the positive and
negative sides, forming an electrical circuit, the
electrons can be captured in the form of an electric
current - that is, electricity. This electricity can then be
used to power a load. A PV cell can either be circular or
square in construction.
Photovoltaic Module
Due to the low voltage generated in a PV cell
(around 0.5V), several PV cells are connected in series
(for high voltage) and in parallel (for high current) to
form a PV module for desired output. Separate diodes
may be needed to avoid reverse currents, in case of
partial or total shading, and at night. The p-n junctions
of mono-crystalline silicon cells may have adequate
reverse current characteristics and these are not
necessary. Reverse currents waste power and can also
D. Dc Filter
This filter is used to reduce the ripple content
present in the output voltage of the converter. The
capacitor is widely used for dc filter. In addition to that
the inductor and the capacitors serve as voltage sources
to extend the voltage gain and to reduce the voltage
stress on the switch. This regulated dc output is given to
the dc load.
III. INTERLEAVED BOOST CONVERTER
A two-phase interleaved boost converter is
usually employed in high input-current and high inputto-output voltage conversion applications. The circuit
diagrams of the two phase interleaved boost converter
with uncoupled, directly coupled, inversely coupled
IBC are shown in figure 2 to 4.
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35
International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
Mode 1 Operation: (0 ≤ t < t1)
At t =0, the gate pulse is given to the switch
‘S1’ of the first phase. Then the switch ‘S1’ is turned
on, the current across the inductor L1 rises linearly. At
the same time, the switch ‘S2’ in the second phase is
turned off and the energy stored in the inductor L2 is
transferred to the load through the output diode D2. In
this time interval, the diode D1 in the first phase is in
reverse bias condition. The circuit operation for Mode-1
is shown in figure 5.
Fig.2 Circuit Diagram for two phase uncoupled
IBC
Fig.3 Circuit Diagram for two phase coupled
IBC
The two phases of the converter are driven 180 degrees
out of phase, this is for the reason that the phase shift to
be provided depends on the number of phases given by
360/n where n stands for the number of phases.
Fig.5 Current paths of IBC in Mode-1
At time t0, S1 is closed. The current in the inductor L1
starts to rise while L2 continues to discharge. The rate of
change of iL2 is approximately given by,
Mode 2 Operation: (t1 ≤ t < t2)
Fig. 4 Circuit Diagram for two phase inversely
coupled IBC
At t = t1, the gate pulse is given to the switch
‘S2’ of the first phase. Then the switch ‘S2’ is turned
on, the current across the inductor L2 rises linearly. At
the same time, the switch ‘S1’ in the first phase is
turned off and the energy stored in the inductor L1 is
transferred to the load through the output diode D1. In
this time interval, the diode D2 in the second phase is in
reverse bias condition. The circuit operation for Mode-2
is shown in figure 6.
Operation of Interleaved Boost Converter:
There are two modes of operation in two phase
interleaved boost converter for renewable energy
applications such as photovoltaic module, fuel cell.
They are,
i) Mode 1operation
ii) Mode 2 operation
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34
International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
for all the phases. The switching pattern for interleaved
boost converter is shown in Fig.7.
Fig.6 Current paths of IBC in Mode-2
At time t1, S2 is closed. The current in the inductor L2
starts to rise while L1 continues to discharge. The rate
of change of iL1 is approximately given by,
IV. DESIGN PROCEDURE FOR IBC
Fig.7.Switching pattern for two phase IBC
The interleaved boost converter design
involves the selection of the number of phases, the
inductors, the output capacitor, the power switches and
the freewheeling diodes. Both the inductors and diodes
should be identical in all the channels of an interleaved
design. In order to select these components, it is
necessary to know the duty cycle range and peak
currents. Since the output power is channeled through
‘n’ power paths where ‘n’ is the number of phases, a
good starting point is to design the power path
components using 1/n times the output power. The
various stages involved in designing interleaved boost
converter are
 Selection of number of phases
 Selection of duty ratio
 Selection of power devices
 Design of inductor
 Design of output filter
B. Selection of duty ratio
Duty ratio also aids in ripple reduction and
hence it has to be selected carefully. From the plot of
the input current ripple versus the duty ratio, it can be
found that for an N-phase IBC, the ripple can be zero at
particular values of duty ratio. The input current ripple
for various duty ratios are shown in figure 8.
A. Selection of number of phases
It has been observed that the ripple in the input
current decreases with increase in the number of
phases. On the other hand, the cost and complexity of
the circuit also increases. So, a compromise had to be
made between them. In this paper, the number of
phases was chosen to be two to reduce the ripple
content without increasing the cost drastically. The
number of inductors, switches and diodes are same as
the number of phases and switching frequency is same
Fig.8 Input current ripple with duty ratio
For a 2-phase converter, the ideal duty ratio at which
the ripple is zero is 0.5.
C. Selection of power semiconductor switches
The semiconductor device chosen for
constructing the two phase interleaved boost converter
is the IGBT. The main benefits of IGBT are lower on-
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35
International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
state resistance, lower conduction losses and high
switching operation. The maximum voltage across the
switching devices is given by
(3)
The value of mutual inductance is given by,
(9)
Where Vin is the input voltage, K is the duty ratio of the
converter. The diode has less forward voltage, high
reverse breakdown voltage and less reverse recovery.
E. Design of Output Filter
A capacitor filter is needed at the output to
limit the peak to peak ripple of the output voltage. The
capacitance of the output filter is function of the duty
cycle, frequency and minimum load resistance during
maximum load. For 5% output voltage ripple, the value
of the capacitance is given by the formula,
D. Selection of Inductors
Design of inductance is very important in
boost topologies so that the inductor is sized correctly.
The design of inductors for uncoupled and directly
coupled IBC is explained as follows:
1. Design of uncoupled inductor
The value of the inductance is given by,
(10)
(4)
Where, R represents the load resistance, Vo represents
the output voltage and T represents the switching
period.
2. Design of coupled inductor
The expression for equivalent inductance of
directly coupled IBC is given by,
V.
(5)
As per the design equations, a two phase
interleaved boost converter with uncoupled, directly
coupled and inversely coupled inductors are simulated
in MATLAB/SIMULINK .The values for uncoupled
IBC are L=2.5mH, C=78µF, f=2KHz.and R=3.2Ω.The
output voltage is Vo=72V, for an input Vin=12V. The
values used for directly and inversely coupled IBC are
summarized as Vin = 12V, R = 3.2Ω, C =78uF,
fs=2kHz, Lm = 7mH, Lkl = Lk2 =4.3mH, Vo =67v,
K=0.5and a = 0.61 for directly coupled.
Where, Vin represents input voltage, K represents duty
ratio. To find out the values of mutual inductance (Lm),
the input current is calculated using the input voltage
and power.
The value of mutual inductance ‘Lm’ is given by,
Lm = α L
SIMULATION RESULTS
(6)
Where, α represents coupling coefficient
Therefore, the overall input current ripple is derived as
(7)
From the above equations it is clear that increasing the
value of the coupling coefficient can effectively reduce
the input current ripple, but the phase current ripple is
increased. Therefore, the value of coupling coefficient
is carefully chosen as 0.61, so that the input current
ripple is reduced and the phase current ripples are
within the limits.
3. Design of inversely coupled inductor
The self-inductance value for inversely
coupled is obtained from the equation is given by,
Fig.9 Input voltage waveform of two phase
uncoupled IBC
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38
International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
Fig.10 Switching pattern for two phase IBC
Fig.13 Inductor current waveform for coupled IBC
Fig.11 Inductor current waveform for
uncoupled IBC
Fig.14 Output Voltage waveform for coupled IBC
Fig.15 Inductor current waveform for inversely
coupled IBC
Fig.12 Output Voltage waveform for uncoupled IBC
39
37
International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
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Fig.16 Output Voltage waveform for inversely
coupled IBC
From the results we conclude that the inductor ripple is
smaller for inversely coupled compared to the others,
still the input current ripple is greater for inversely
coupled IBC. We distinguish that whenever the
inductor current ripple is less, efficiency is more. The
higher value of input current ripple of inversely coupled
is not apt for certain applications. This higher current
ripple can be reduced by selecting correct value of duty
ratio and coupling coefficient. The results show that the
directly coupled IBC provides a reduced input current
ripple which is best suitable for photovoltaic module
applications.
VI. CONCLUSION
Interleaved boost converter has so many merits
and is a proper converter for renewable energy
applications. Three cases of IBC using uncoupled,
coupled and inversely coupled inductor have been
considered for renewable energy applications. Their
design equations have been presented and performance
parameters of all three cases have been related using
simulation. It is demonstrated that the directly coupled
interleaved DC-DC converter efficiently reduces the
overall current ripple related to that of uncoupled
inductors. Therefore directly coupled IBC is a right
choice for photovoltaic module.
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International Journal of Power Control and Computation(IJPCSC)
Vol5.No.2 2013 pp 34-41
available at: www.ijcns.com
Paper Received :05-05-2013
Paper Accepted:28-05-2013
Paper Reviewed by: 1. James Durai Raj 2.Ms. A. Abirami
Editor : Prof. P.Muthukumar
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