A High Static Gain Modified SEPIC Converter With PV Module and MPPT

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 01 | Jan -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 835
A High Static Gain Modified SEPIC Converter With PV Module and MPPT
Jayashri E. Patwardhan1 , Ruchita Maheshwari 2
1 PG Scholar, Department of Electrical and Electronics Engineering, Marathwada Institute of Technology (MIT),
Aurangabad, Maharastra, India
2 Assistant Professor, Department of Electrical and Electronics Engineering, Marathwada Institute of Technology
(MIT), Aurangabad, Maharastra, India
---------------------------------------------------------------------***---------------------------------------------------------------------
ABSTRACT - Photovoltaic (PV) energy is one of the most
important energy resources in renewable power generation
since it is clean, pollution free, and endless. In photovoltaic
(PV) systems to maximize the photovoltaic output power,
Maximum Power Point Tracking (MPPT) is used irrespective
the variations of temperature and radiation conditions. This
paper presents two topologies of modified single-ended
primary inductance converter (SEPIC) without magnetic
coupling and with magnetic coupling for photovoltaic
(PV)application. The single-ended primary inductance
converter (SEPIC) is used in applicationwithlowinputvoltage
and output voltage is considerably high. Proposed topologies
based on modification of single-ended primary inductance
converter (SEPIC )converter with voltage multiplier .With the
proposed modification the static gain of the DC-DC- Converter
increases Both the topology provides thehighstaticgain with
the low switch voltage, reduce reverse recovery current of
output diode for low input voltage renewable application. The
two converters and MPPT algorithm were modeled using
MATLAB/Simulink software for simulation. Simulationresults
show that both the topologies without and with magnetic
coupling provides high static gain for renewable application
with low input voltage.
Key Words : DC-DC converter, Voltage multiplier , PV Cell,
MPPT,SEPIC
1.INTRODUCTION
Due to increasing electrical energy demand and
limitation of fossil fuels; renewable power generation is the
most importance in power sector. Low power wind turbine,
photovoltaic (PV) modules are the some examples of
renewable energy. The generation of energy in PV modules
depended upon the environmental conditions, solar
irradiation,module temperature.
To obtain the maximum power extraction to all
environmental condition the maximum power point
tracking(MPPT)is essential. Though the efficiencyofmodule
depends on the MPPT which force the module to operate
with maximum efficiency.
To interface with utility gridthehighstatic gainDC-
DC converter to be used. There are many researches are
going on to get high static gain dc–dc converters for
applications supplied from low dc output voltage power
sources. Applications like embedded systems, portable
electronic equipment’s, uninterruptable power supply, and
battery powered equipment required reduced losses, high
power density, low weight, and volume.
The proposed converters can be used in the
photovoltaic energy generation in grid-connected systems
used in ac module or micro inverter structure. PV systems
suffer from a major drawback which is the nonlinearity
between the output voltage and current particularly under
partially shaded conditions. However, the development for
improving the competence of the PV system is still a
demanding field of research. Generally, MPPT is adopted
Fig.1 Two stage Ac Module Structure.
to track the maximum power point in the PV system. The
P&O Maximum Power Point Tracking algorithm is mostly
used because of its simple structures and fewer parameters.
The conversion power is important to solar power
generation systems because it converts the dc power
generated by a PV array into ac power and feeds to ac power
into the utility grid.
To obtain the DC voltage level necessary for the
inverter operation and energy transferred to the grid with
low-current harmonic distortion usuallyinhigh-powergrid-
connected photovoltaic generation PV modules are
connected in series. Problem due this structure are, power
losses due to the centralized maximumpowerpointtracking
(MPPT), mismatch losses among the PV modules, and
generation reduction due to a partial shading of the series-
connected PV modules. By using Multistring structurethese
problems can be rectified where reduced strings are
connected with dc–dc converters with the MPPT algorithm
and the output of these dc–dc converters are connected to
the inverter input. For domestic based application most
research is focused on the module-integrated converters
where energy generated by the PV module is transferred to
the grid through the high gain converter they can integrated
with the PV module system. Such PV generation structure
have advantages like modularity, allowing an easy increase
of the installed power, the individual MPPT and reduction of
the partial shading and panel mismatching effects, thus
improving the energy-harvesting capability. But with these

structure some design challenges in ac module system are
efficiency improvement, cost reduction, and the reliable
operation throughout the module lifetime.
F
Fig.2 Modified SEPIC Converter without
magnetic coupling
The ac module implementation is a two-stage topology as
presented in Fig. 1. For the dc–dc converter due to the low
input voltage, high input current, high output voltage, and
static gain operation with high efficiency is critical. For the
implementation of the first power stage high step-up ratiois
necessary, the usual solution is the use of isolated dc–dc
converters. The transformer turnsratioallowsustoincrease
the converter static gain. However, the isolated solution
presents some problems as the efficiency reduction due to
the power transformer losses and intrinsic parameters as
the leakage inductance. Use of power transformer increase
the converter weight and volume.
Due to the high cost of the energy source, as
photovoltaic module or fuel cells; The power converters
used with renewable energy sources must present a high
efficiency. The boost converteristheclassical solutionbut its
gives limited gain with duty cycle not more than 0.8. In this
paper three static gain are considered; static gain equal to q
=5 is limited. A dc–dc converter operating with a static gain
range until q = 5 is considered a standard static gain, a static
gain range higher than q= 10 is considered a high static gain
solution and an operation with static gain higher than q =20
is considered a very high static gain solution.
The base topology presented in this paper is a
modification of the SEPIC dc–dc converter with this
modification we obtained operation characteristicswiththe
requirements necessary in the high static gain applications.
The without magnetic coupling structure gives static gain
double of classical boost converter where as switch voltage
half of the boost converter. In the structure with magnetic
coupling secondary inductor acts as flyback transformer
which increasing the static gain. Only part of power transfer
through coupling inductor which reducing the stress on
output diode, weight and volume of converter.
2. SEPIC CONVERTER WITHOUT MAGNETING
COUPLING
2.1 Power Circuit without magnetic coupling
In fig. 2 the power circuit of modified SEPIC converter is
present. The static gain of the SEPIC converter is an either
step up or step down. In which the switch voltage is equal to
the sum of input and output voltage. In some application the
sum of the input voltage and output voltage is equal to the
Switch voltage and static gain is lower than the classic boost
converter. By adding two component i.e. diode and DM and
Capacitor CM in the SEPIC converter. With this modification
many characteristics are change with this converter. The
static gain of the modified SEPIC converter is increased by
double than classical boost converter with the high duty
ratio. But practically the limitation of this converter is we
cannot exceeds duty ratio above 0.85.
Fig.3. First stage
Consider converter CCM mode it includes two
stages. For analysis assume all capacitors asa voltagesource
and semiconductors to be ideal.
Fig. 4. Second operation stage
1) First Stage[t0-t1] (Fig.3) : In this stage switch S is
turns-off at an instant t0 and the diodeDM andDO are
forward biased . The stored energy in L1 gets
transfer to the output through the CS and DO and
also it gets transfer to CM through DM . Due to this
the switch voltage is equal to the Cm voltage.
Energy stored in L2 gets transfer to output.
2) Second Stage[t1-t2](Fig.4): In this stage switch S
turns-on at an instant t1 the diodes DM and DO gets
block and energy gets store in the inductors L1 and

L2. input inductor L1 charges with inputvoltage and
inductor L2 charges with the voltage VCM - VCS.
The maximum voltage in all diodes and the power
switch is equal to the CM capacitor voltage. The sum of
the CS and CM capacitors voltage is equal output voltage.
Input current is equal to average L1 inductor current,
and output current is equal to the average L2 inductor
current. At the steady state the static gain of the
proposed convertercanbeobtainedconsidering null the
average inductors voltage and it is presented in (1)
considering the CCM operation. The static gain of the
proposed converter is higher than the obtainedwiththe
classical boost.
VCM voltage is equal to the maximum switch voltage.The
switch voltage is lower than the output voltage and
calculated by (2)
Capacitor Voltage is Calculated by (3)
The operation stages and theoretical waveforms of
proposed converter without magnetic coupling
presented in this paper.
Fig.5 Theoretical waveforms
3. PROPOSED CONVERTER WITH MAGNETIC COUPLING
Power Circuit With Magnetic coupling
Fig.6 SEPIC Converter With Magnetic Coupling
Proposed converter shows double the Static gain
with high duty cycle of conventional Boost Converter.
However sometimes a very high Static gainisvery necessary
for certain application to maintain the converter
performance steady at all operating conditions is the
practical limitations. We cannot increase duty ration above
85% in practice. By adding secondary winding to inductor
we can solve this problem. But by adding secondary winding
the output voltage increase which cause overvoltage at
output diode. This overvoltage is not controlled easily by
conventional overvoltage protection. By providing the
voltage multiplier at the secondary side can solve the
problem. Employing voltage multiplier at secondary reduce
overvoltage at output diode, energy transferred directly to
output. Fig.6 shows the power circuit of proposed.
The CCM operation of modified SEPIC converter
with magnetic coupling and output diode clamping having
five operating stages.
Fig. 7. First operation stage.
Fig. 8. Second operation stage.

Fig. 9. Third operation stage.
F
Fig. 10. Fourth operation stage.
Fig. 11. Fifth operation stage.
1. First stage[t0-t1](Fig.7): The Switch S is conducting
and L1 is store the charge. By using the secondary
winding the capacitor is get charged. The leakage
inductance limits the current and energytransferin
a resonant way.
2. Second Stage [t1-t2](Fig.8): DM2 is get blocked from
the t1, the instant t2 the power is switch off. and the
inductor store the energy L1 and L2.
3. Third Stage[t2-t3](Fig.9): The switch is turned off at
the time t2. L1 stores the energy to the Capacitor CM
4. Fourth Stage[t3-t4](Fig.10) : At time t3, energy get
transfer to the capacitor CM. and the diode D1 is
blocked.
5. Fifth Stage[t4-t5](Fig.11): When the Power switchis
turn on at t4,the current is linearly decease D0.
The main theoretical waveforms of the modified SEPIC
converter with magnetic coupling and with the voltage
multiplier at secondary side are presented in Fig. 12. The
switch voltage and the voltage across the diode is low as
compare to the output voltage. The switching losses are
reduce when the switch get turn on. Due to the coupling
Fig. 12. Main theoretical waveforms of the modified
SEPIC converter with magnetic coupling and voltage
multiplier at the secondary side
inductor the current variations in all diodes, reducing the
negative effect of the diode reverse recovery current.
The static gain of the modifiedSEPICconverterwith
magnetic coupling and voltagemultiplieriscalculatedby(4).
where the inductor windings turns ratio (n) is calculated
by
Fig. 11. Fifth operation stage.

4.SIMULATION RESULTS
Using MATLAB /SIMULINK software model of single-ended
primary inductance converter (SEPIC) without magnetic
coupling and with magnetic coupling modeled and
simulated. The parameters for preferred converter without
magnetic coupling and with magnetic coupling are shownin
table
Simulation results for without magnetic coupling
Fig -1: Name of the figure
Fig.13 Input/Output Voltage, Current waveforms
Simulation results for with magnetic coupling
Fig.14 Input/Output Voltage, Current waveforms
Parameter used for simulation and design of converter are
stated in table1 .
Table -1: Parameter
Parameters
Modified
SEPIC
converter
without
magnetic
coupling
Modified
SEPIC
converter
with
magnetic
coupling
Input Voltage(Vi) 15V 15V
Output
Voltage(Vo)
150V 300V
Output Power(Po) 100W 100W
Switching
Frequency(f)
24KHz 24KHz
Duty Cycle(D) 0.82 0.82
Switch
Voltage(Vs)
83V 83V
Static Gain(q) 10 20
5. CONCLUSIONS
The static gain of the proposed modified SEPIC converter
without magnetic coupling is q=10;where as with magnetic
coupling and voltage multiplier is q=20. From the result
obtain for without magnetic coupling and with magnetic
coupling and voltage multiplier of proposed topology are
giving high static gain for the renewable application with
reduced switch voltage improved efficiency and reduced
weight and volume.
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