Matlab simulink based-analysis of photovoltaic array fed multilevel boost converter

Innovative Systems Design and Engineering www.iiste.org
ISSN 2222-1727 (Paper) ISSN 2222-2871 (Online)
Vol.4, No.7, 2013 - National Conference on Emerging Trends in Electrical, Instrumentation & Communication Engineering
20
Matlab /Simulink Based-analysis of Photovoltaic Array Fed
Multilevel Boost Converter
Praveen bansal1
Department of Electrical Engineering, Maulana Azad National Institute of Technology, Bhopal (M.P)
1
Email-pbansal44@rediffmail.com
Abstract
The increasing private sectors are focusing employment of eco friendly renewable/green power technologies
like PV Cells, Fuel Cells, Wind turbine to meet the growing power demand. This paper presents the analysis and
operation of PV system using Multilevel DC to DC Boost Converter Topology .The DC to DC Multilevel Boost
converter is based on one inductor, one switch, 2N-1diodes and 2N-1 capacitors, for an Nx converters, it is a
boost converter able to control and maintain the same voltage in all the N output levels and able to control the
input current. The proposed model and their performance are evaluated for varying loads in MATLAB/Simulink
environment.
Keywords – PV array , Multilevel boost converter ,Matlab, simulink
1. Introduction
Increased energy utilization and global pollution awareness have made green/renewable power more and more
important for stand alone as well as distributed generation. Wind turbines, Photovoltaic and Fuel Cells are
different types of green power technologies. Photovoltaic systems have been extensively employed for large
power generation around the whole world in recent decades. The conversion of solar energy into electric energy
is performed by means of photovoltaic cells.
In order to adapt the output Voltage of the energy supplies/storage systems the medium voltage level, boosting
of the DC voltage is required. For large voltage step-up ratios this task is advantageously performed by DC- DC
converters[1]. Since the PV array delivers Dc power, it must be inverted to AC and stepped-up to be able to use
for household applications as well as for distributed generation and output voltage is regulated desired level.
Therefore a suitable Power electronic interface is required between PV array and load, with the capabilities of
balance output voltage.
Above task can be achieved by connecting a DC-DC converter with voltage gain to the PV array.The proposed
model of renewable energy fed Multilevel Boost converter using Matlab/simulink is given Figue(1).
PROPOSED MATLAB /SIMULINK MODEL OF PV ARRAY FED MULTILEVL BOOST CONVERTER
Figure1 .Proposed Multilevel Boost Converter for PV array Application.

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Several topologies of switched mode DC-DC converter followed by dc source are proposed and compared based
on their performance. A switch mode DC-DC converter is preferred to limit the size and cost of the system. A
current fed DC-DC converter is preferred over the voltage fed DC-DC converter as the former requires reduced
input filtering. A push pull DC-DC converter is selected with voltage gain to reduce the switches conduction
losses. However, its use is restricted to own ad medium power applications. Full bridge topology is preferred for
high power applications as push-pull topologies have a serious problem of centre tap termination, which tends to
cause saturation of the transformer at high power levels, though a full bridge requires more switches of half
rating, which is more economical & efficient.
All these topologies discussed above, uses multiple stage conversion to deal with the above mentioned
challenges, which results in large component count, therefore poor reliability, additional cost, and low efficiency.
In addition to this, energy storage devices such as battery and ultra capacitors are also needed at various stages
either to supply auxiliaries or to improve the slow transient’s response of the PV array.
2. MODELLING OF PV ARRAY
The building blocks of PV array are the solar cell, which is basically a p-n junction that directly converts light
energy into electricity, it has a equivalent circuit as shown below in figure….
Figure.2 Electrical Circuit of PV Module
The current source Ipv represents the cell photo current ,Rshunt and Rs are used to represent the intrinsic series
and shunt resistance of the cell respectively. Usually the value of Rshunt is very large and that of Rs is very
small, hence they may be neglected to simplify the analysis .PV cells are grouped in larger units called PV
modules which are further interconnected in series –parallel configuration to form PV arrays [2].The PV
mathematical model used to simplify our PV array is represented by the equation .
I=np*Iph-npIrs[exp((qv)/(KTAns))-1] …………………………………………………………..(1)
Where I is the PV array output current ,V is the PV array output Voltage ,ns is the number of cells in series and
np is the number of cells in parallel, q is the charge of an electron , k is the Boltzmann constant , A is the p-n
junction ideality factor, T is the cell temperature (K),Irs is the cell reverse saturation current. The factor A in
equation determines the cell deviation from the ideal p-n junction characteristics it ranges between 1-5 but for
our case A=2.46 [3].
The cell reverse saturation current Irs varies with temperature according to the following equation:
Irs=Irr{(T/Tr)3}exp[{(qEG)/(KA)}*{(1/Tr)-(1/T)}]……………………………………………….(2)
The temperature dependence of the energy gap of the semi conductor is given by
EG=EG(0)-{αT2/(T+β)}…………………………………………………………………………………..(3)
The photo current Iph depends upon on the solar radiation and cell temperature as follows:
Iph=[Iscr+Ki(T-Tr)]*(S/100)…………………………………………………………………………….(4)
The Power can be calculated as
P=VI=npIphV[{(qv)/(KTAns)}-1]………………………………………………………………………(5)

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2.1 Voltage-Current charactersistcs of PV Array under a fixed irradiance but varying temp.
Figure3.VI characteristics of PV Array
2.2 P-V characteristics of a solar array for a fixed temperature but varying irradiance
Figure4. PV characteristics of PV Array
2.3 P-V Characteristics of a PV array under a fixed irradiance bur varying temperatures
Figure5. PV Characteristics of PV Array

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2.4 Simulink model of Photovoltaic array
Figure 6. Simulink Model of Photo Voltaic Array
2.5 Parameters Value used in PV Array
Parameters Values
Np 4
Ns 60
Iscr 3.75 A
Tr1 40 C
Ki 0.00023 A/K
Irr 0.00021 A
K 1.38065*10-23 J/K
q 1.6002*10-19 C
A 2.15
Eg(0) 1.66 eV
α 4.73*10-4 eV/K
β 636 K
3. MODELLING OF DC-DC MILTILEVEL BOOST CONVERTER
Figure.7. shows the multilevel boost converter “MBC”. An Nx MBC is based on one driven switch 2N-1 diodes
and 2N-1 capacitors , the number of levels can be extended by adding capacitors and diodes and the main circuit
does not need to be modified[4].
The lower part of the converter is the conventional Boost Converter, then the voltage gain also holds for the well
know boost converter equations. The difference between the multilevel boost converter and the conventional one
is that in the multilevel boost converter the output is Vc ,times N, where N+1 is the converter’s number of levels
take into account the zero level. This behavior is achieved thanks to the voltage multiplier in the output of the
boost converter which is driven by the switch in the converter.

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Figure 7.Multilevel DC-DC boost converter for Nx and Nx+1 levels
3.1 TURN ON AND TURN OFF STATES
The multilevel principle of this converter will be explained through a 4x( 5 levels) DC-DC boost converter .To
explain the multilevel principle explain ,assume that the switch (s) is switching with a duty ratio(d) of 0.5.
During the switch-on state , the inductor is connected to Vin voltage.Figure 8a. If C6 voltage is smaller than C7
voltage then C7 clamps C6 voltage through D6 and the switch S. Figure 8b.At the same time if the voltage
across C4 +C6 is smaller than the voltage across C5 + C7 , then C5 and C7 clamps the voltage across C4 and C6
through D4 and S. Figure 6c . In a similar C3 , C5 and C7 clamps the voltage across C2 ,C4 and C6 in Figure d.
Figure 8. Turn On state of Multilevel Boost Converter
When the switch turns off , the inductor current closes D7 , and switches all diodes , During the switch Off state ,
the inductor current closes D7 charging C7.Figure 9a.When D7 closes , C6 and the voltage in Vin plus the
inductor’s voltage clamp the voltage across C5 and C7 through D5 Figure 9b,Similarly the voltage across C3 ,
C5 and C7 through D3. Finally the voltage across C1 ,C5, C3 and C7. Is clamped by C2 ,C4 , C6, Vin and the
inductor voltage in Figure 9c. It is noteworthy that D1, D3 ,D5 and D7 switch in a synchronously way ,
complemented with D2 , D4, D6 and S.

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Figure 9. Turn Off state of Multilevel Boost Converter
3.2 DESIGN SPECIFICATION OF MULTILEVEL BOOST CONVERTER
Specification Values
Input Voltage 20-30 V
Output Voltage 250-320( DC )
Switching Frequency(f) 10 KHz
Duty Cycle (D) 0.4 < D < 0.8
Inductance (L1) 20mH
Capacitance 110 µF
Switch Type Mosfet
The transfer function of Conventional Boost converter is .
Vout = Vg
1-D
But in the Multilevel Converter the transfer function is
Vout = Vg*N
1-D
It is shown from last two equations that the Multilevel Boost converter has a big conversion ratio without
extreme duty cycle depending on the level of it[5].
4. SIMULATION RESULTS
The simulink model of the Photovoltaic array fed Multilevel Boost Converter is modeled in Figure.1 using
Matlab/simulink environment.The simulationwork is carried out for a triangular waveform of 10Khz switching
frequency for the Multilevel Boost converter its switching pattern model is shown in figure9.

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The waveform of switching pulse generation for Mosfet is shown in figure.10 and Figure.11
Figure10. Triangular waveform for Switching pulse generation
The Waveform of switching pulse generation is shown in Figure.11
Figure.11 Switching pulse generation
Waveform of Input voltage of Photovoltaic array is shown in Figure.12
Figure.12 Input voltage
Waveform of Input current of Photovoltaic array is shown in Figure.13
Figure.13 Input curremt
Waveform of Output Voltage is shown in Figure.14
Figure.14 Output voltage
5. CONCLUSION
The open circuit P-V, P-I and I-V curves we obtained from the simulation of the PV array designed in MATLAB
environment explains in detail its dependence on the irradiation levels and temperatures. The entire energy
conversion system has been designed in MATLAB-SIMULINK environment. The various values of the voltage
0 1 2 3 4 5 6 7 8
x 10
-4
0
0.5
1
Time in secs
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
x 10
-3
-1
-0.5
0
0.5
1
1.5
2
Time in axis
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
0
10
20
30
40
Time in secs
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
-20
-10
0
10
20
Times in Secs
InputPVArraycurrent

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and current obtained have been plotted in the open circuit I-V curves of the Photovoltaic array at insolation
levels of 100mW/cm2 and 80mW/cm2.The Voltage and current values lie on the curve showing that the
coupling of the PV array with the Multilevel Boost Converter is proper[6]. However the performance of the
photovoltaic device depends on the spectral distribution of the solar radiation.
6. REFERENCE
MAKSIMOVIC D, CUK S:,’ Switching Converters with wide Dc conversion range’, IEEE Trans. Power
Electronics , 2001,6.(1) , pg. No. 151-157.
I.H Atlas , A.M sharaf ,” A photovoltaic Array Simulation Model for Matlab-simulink GUI Environment ,”
Proce. of IEEE International Conference on clean Electrical Power ,ICCEP 2007 , Capri, Italy.
Quan Li and Peter Wolfs ,” A Review of the Single Phase Photovoltaic Module Integrated Converter Topologies
With three Different DC link Configurations” IEEE Transactions on Power Electronic , Vol.23,No.3 , May 2008,
pg. No. 1320-1331.
Geoffrey R. Walker , and Paul C.Sernia, “ Cascaded DC-DC converter connection of photovoltaic
Modules,”IEEE Transaction on Power Electronics,Vol.19 ,July 2004 , pg. No. 1130-1139.
Julio C. Rosas-Caro, Juan M. Ramirez, Pedro Martin Garcia-Vite , “ Novel DC-DC Multilevel Boost Converter .”
Proc. IEEE Power Electronics specialists Conference, 2008.
AXELROD B., BERKOVICH Y., IOINOVICI A.,: ‘ A cascaded boost- switched –capacitor-converter – two
level inverter with an optimized multilevel output waveform,” IEEE Transaction circuits sys. I, 2005 , 52 , (12),
pg. No. 2763-2770.
FAN Z.,PENG F.Z. , ZHAOMING Q: ‘ Study of the multilevel converters in DC-DC applications’, IEEE 35th
Annual Power Electronics Specialists Conf, PESC 04 , 2004 , Vol. 2, pg. No. 1702-1706.
MIDDLEBROOK R.D:, ‘Transformerless DC-DC Converters with large conversion ratios,’ IEEE Trans. Power
electronics, 1988, 3 (4), pg. No. 484-488.

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