Paper 5 - IJAST Sep 2012 by rakeshun

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									                                                                  International Journal of Advances in Science and Technology,
                                                                                                             Vol. 5, No.3, 2012


    A High Voltage Gain Switched Inductor
  Multilevel Boost Converter for PV Applications
                P.GANESH KUMAR                                                           G. BALAJI
               M.Tech Student Scholar                                                  Asst Professor
 Department of Electrical and Electronics Engineering,             Department of Electrical & Electronics Engineering,
 Gudlavalleru Engineering College; Gudlavalleru(M);                 Gudlavalleru Engineering College; Gudlavalleru(M);
               Krishna(Dt); A.P, India.                                           Krishna(Dt); A.P, India
        e-mail: papisettiganesh@gmail.com                                    e-mail: gutta_balaji@yahoo.co.in

Abstract- In dc-to-dc conversion applications that require a        The main multilevel converters’ applications are focused in
large range of input and/ or output voltages, conventional         high power motor drives, static VARs compensation, and
PWM converter topologies must operate at extremely low duty        other utility applications they are also suitable for FACTS
ratios, which limits the operation to lower switching              devices. They can also been applied to DC-DC conversion
frequencies because of the minimum ON time of the switch.          in low power, especially for automotive applications, and
This is eliminated in a new class of single switch PWM
converters featuring high voltage gain conversion ratios. In
                                                                   renewable energy systems.
this paper presents a new single stage dc – dc boost converter
topology with very large gain conversion ratio as a switched          Renewable energy sources such as photovoltaic’s, fuel
inductor multilevel boost converter (SIMLBC). It is a PWM-         cell and wind energy generate their power at very low dc
based dc- dc converter which combines the Switched Inductor        voltage which is not suitable for generating the ac supply
structures and the switching capacitor function to provide a       with 110 or 220v directly. The conventional dc- dc with low
very large output voltage with different output dc levels which    dc conversion ratio is not suitable for these applications
makes it suitable for multilevel inverter applications. The        unless many of these sources are connected in series to
proposed topology has only single switch like the conventional     increase their net dc voltage. Unfortunately sometimes
dc- dc converter which can be controlled in a very simple way.
In addition to, two inductors, 2N+2 diodes, N is the number of
                                                                   connection of many renewable energy sources in series
output dc voltage levels, and 2N-1 dc capacitors. A high           decreases their efficiency. There are some proposed
switching frequency is employed to decrease the size of these      solutions for increasing the dc- dc gain conversion ratio of
components and thus much increasing the dynamic                    dc converters. First solution is to use of cascaded of
performance. Here we proposed a new topology of boost              converters increase the conversion ratio which is a no-
converter implemented by using PV cells; the system is             solution in the today’s energy saving conscious world, as
evaluated using Matlab/Simulink Platform.                          this procedure implies an overall efficiency equal to the
                                                                   product of the efficiencies of each circuit. The second
Keywords- Switched Inductor Boost Converter (SIBC), Multilevel
                                                                   solution is to use the quadratic converters which can
Boost Converter (MLBC), and Power Conditioning System
(PCS), Photo-Voltaic (PV) System.                                  somehow alleviate the efficiency problem but they many
                                                                   present voltage or current overstresses.

                      I.   INTRODUCTION                            In photovoltaic systems, solar energy is converted into
     Multilevel converters have attracted interest in power        electrical energy by photovoltaic (PV) arrays. PV arrays are
conversion, they already are a very important alternative in       very popular since they are clean, inexhaustible and require
high power applications [1] It has been shown that they are        little maintenance. Photovoltaic systems require interfacing
useful in virtually all power conversion processes such as         power converters between the PV arrays and the load.
ac-dc, dc-ac, dc-dc and ac-dc-ac Some of the advantages of
multilevel converters against traditional topologies are: (i)           A better solution is to use a dc- dc converter with steep
low harmonic distortion, (ii) low voltage stress, (iii) low        step- up conversion ratio. By looking to the literature there
EMI noise, (iv) low switching frequency, (v) high                  are a less number of dc-dc converters with very high gain
efficiency, (vi) ability to operate without magnetic               conversion ratio. Two types of the dc – dc for high dc gain
components. All these advantages make multilevel                   conversion ratio is switched inductor boost converter and
converters one of the most important topics in power               multilevel boost converter. This work proposes a new
electronics, and industrial application research, and in some      topology based on the two topologies that have a very high
applications they can get modular topologies [2].                  conversion ratio without scarifying its performance. The
                                                                   proposed system is suitable for utility applications such as
                                                                   ac modules. Distributed power supplies are expected to
                                                                   become increasingly prevalent in the near future, they




    September Issue                                       Page 28 of 132                                     ISSN 2229 5216
                                                                        International Journal of Advances in Science and Technology,
                                                                                                                   Vol. 5, No.3, 2012

requires a power conditioning system (PCS) to control the
frequency and voltage output from renewable energy
sources. It is a must to transfer energy from these sources
into utility grids at unity or near unity power factor. The
system block diagram is shown of Fig.1.




                                                                                       Fig. 2. The schematic diagram of SIMLBC
     Fig. 1. The block diagram of dc- ac PCS with dc-dc SIMLBC

As mentioned these applications require a converter that                  The two operation modes of this topology are indicated in
converts a small voltage to a high voltage so the converter               Fig. 3 and 4. When the switch on, the two inductor is
should have a high boosting ratio. One candidate is                       connected to the voltage source through Ds1 and Ds3. If
transformer-isolated boost topologies, however these                      C 3 ’s voltage is smaller than C 1 ’s voltage then C 1 charging
converters have low efficiency as the boosting ratio of the               C 3 through diode and the switch as shown in Fig. 4. When
transformer becomes higher. So this paper proposes a new                  the switch turns off, the diodes and will be reversed and the
                                                                          diodes D s1 and D s3 will be reversed and the diodes D s2
transformer–less high voltage gain converter and proposed
                                                                          and D 1 will turn on because the two inductors charge the
system implemented by using the PV arrays. It is a switched               capacitor C 1 until the voltage on the capacitor C 1 is equal to
inductor multilevel boost converter as a high gain dc-dc                  the summation voltage on the source and the two inductors
converter to feed any applications that require high dc                   voltage. After that, the diode D 3 turns on, thus the input
voltage or to feed multilevel inverter that is used in ac                 source , the two inductors and capacitor C 3 charge the
applications that requires low total harmonic distortions.                capacitors C 1 + C 2 through it. When the voltage on the C 1
                                                                          + C 2 is equal to the summation voltage on the input source,
                                                                          the voltage on the two inductors and the voltage on the
       II.   THE PROPOSED TOPOLOGY SIMLBC                                 capacitor C 3, then diode D 3 then turns off as shown in Fig.
               OPERATIONAL MODES                                          4.

   Fig.2. shows the schematic diagram of the proposed
topology SIMLBC. It consists of two inductors, 2N+2
diodes; N is the number of the dc output voltage levels, and
2N-1 dc capacitors. Likewise, the operation of the proposed
SIMLBC is almost same like the operation of the
conventional boost converter since it has only single
electronic switch. The main difference between the
conventional boost converter and the SIMLBC is the input
coil. In the SIMLBC, the coil has been replaced by two coils
named a switched coil.




                                                                                          Fig.3. Mode 1 switch is in ON state




    September Issue                                              Page 29 of 132                                          ISSN 2229 5216
                                                                         International Journal of Advances in Science and Technology,
                                                                                                                    Vol. 5, No.3, 2012




                                                                                                 Fig. 5. Conventional Boost Converter.

                                                                           But at the switched inductor multilevel boost converter the
                                                                           equation of the inductor on the ideal will be

                                                                                        �������� = ������������ ���� + (������������ \2 − ����0 \2����)(1 − ����)                     (5)
                  Fig. 4. Mode 2 switch is in OFF state.
                                                                           So the gain ratio of the new topology will be as follows:


                                                                                     ����0 \������������ = ����(1 + ����)\1 − ����             (6)
 III.     ANALYSIS STUDY OF THE PROPOSED SIMLBC                            Taking into account the ESR of the inductor for both the
                                                                           conventional boost converter and SIMLBC, equation (1) can
                                                                           be modified as follows:

                                                                            �������� = ����(������������ − ����1 ����1 ) + (1 − ����)(������������ − ����0 − ����1 ����1 ) = 0
Fig.3. shows the conventional boost converter that consists
of the one inductor, one capacitor, one diode and one                                                                                                         (7)
switch. Equation (1) describes the average voltage of the
inductor on the ideal conventional boost converter as                      Then from equations (4) and (7), the gain conversion ratio

                    �������� = ����(������������ ) − (1 − ����)(������������ − ���� )
follows.                                                                   will equal to

                                                            ����     (1)                       ����0 \������������ = 1\1 − ���� + �������� (1 − ����)����0                        (8)
The steady state voltage on the capacitor the output voltage

                                                                               ����0
                                                                                  ����� = 1� 1 − ����
                                                                           And for the SIMLBC, equations (5) and (6) will result in:


                                                                                                           �������� ����
is governed by equation 4:
                           ����0
                                                                                                     +                            (9)
                                                                                          ����(1 + ����) ����0 (1 − ����)
                                                                                     ��������
                          ������������
                                   = 1/(1-D)                       (2)

The equation of the inductor current is obtained by equating               From (8) and (9), the output voltage of the proposed
                                                                           topology is larger than the conventional boost converter

                  ���������������� = ����0 /����0
the input and output powers and neglecting the losses as
                               2
follows.                                                                   with N×(1+D) where N is the dc output voltage levels and D
                                                                           is the duty cycle. The design values for the inductors and

                   �������� = ����0 /������������ ����0
                            2
                                                                           capacitors of the SIMLBC can be found from the
                                                                   (3)     conventional boost converter by replacing the voltage gain
From (2) and (3) the inductor current is:                                  conversion ratio as given in (10) and (11) below:


                    �������� = ����0 /(1 − ����)����0
                                                                                                      ����(1−����)2 ����
                                                                   (4)

                                                                                                           2����2
                                                                                                 L=                                                          (10)

                                                                                                                                                         ���� =
                                                                                                                    ����������������
                                                                                                           ����
                                                                                                       �������� ∆��������
                                                                                                                                                             (11)




        September Issue                                           Page 30 of 132                                                            ISSN 2229 5216
                                                                 International Journal of Advances in Science and Technology,
                                                                                                            Vol. 5, No.3, 2012

Thus the relation between input and output voltages is equal      the cell generates charge carriers that originate an electric
to the input voltage multiplied by the levels of the converter    current if the cell is short circuited.
multiplied by the (1+duty cycle) and divided on (1-duty
cycle). The main advantages for this topology are the output
voltage can be increased by increasing the levels of the
SIMLBC by add a capacitors and diodes without changing
the main circuit. Also, the voltage stress on the switch is
smaller than the conventional boost converter. Again the dc
gain conversion ratios of the SIMLBC, MLBC, SIBC, and
the conventional boost converter can be summarized in the          Fig. 6: Equivalent Circuit of a PV Device including the series and parallel
following equations. The dc gain conversion ratio of the                                           Resistances.



                          =
MLBC [5] is as follows:

                  ����0          ����
                                                                  The equivalent circuit of PV cell is shown in Fig. 6. In the

                 ������������       1−����
                                                        (12)      above diagram the PV cell is represented by a current source
                                                                  in parallel with diode. Rs and Rp represent series and


                         =
The dc gain conversion ratio of the SIBC [4] is as in (13)        parallel resistance respectively. The output current and
                 ����0         (1+����)
                                                                  voltage from PV cell are represented by I and V

                ������������        1−����
                                                        (13)

Equations (2), (6), (12), and (13) describe the dc gain
conversion ratio of the conventional boost converter,
SIMLBC, MLBC, and SIBC, respectively. It can be noted
that the dc gain conversion ratio of the SIMLBC is the
highest values among them. This is the main advantage of
this new topology. Fig. 6 gives a comparison among the
four aforementioned topologies in the ideal case at different                         Fig. 7. V-I Characteristic of PV Cell
duty cycles. It can be clearly noticed that from this figure
                                                                  The I-V Characteristics of PV cell [7] is shown in Fig.7.
that for low duty cycle the dc gain conversion ratios of these
                                                                  The net cell current I is composed of the light- generated
converters have no much difference. However, for duty
                                                                  current Ipv and the diode current Id
cycle greater than 0.5, a very big difference can be noticed

                                                                                             ���� = ������������ − ��������
among these topologies. Also the dc gain conversion ratio of
the SIMLBC becomes much higher for duty cycle greater                                                                                        (14)
than 0.5 compared to the other three topologies. So it is
preferred to operate this converter for duty cycle larger than    Where
50% and smaller than 90% for getting on higher dc gain
conversion ratio. The second advantage of the SIMLBC is           Id � Io exp�qV⁄akT�
the voltage stress in the components due to using the             Io = leakage current of the diode
multilevel behavior. The stress voltage depends on the level      q= electron charge
of the SIMLBC because the voltage on the switch when it is        k = Boltzmann constant
in the off state equals to the output voltage divided by the      T= temperature of pn junction
number of levels of the converter.                                a= diode ideality constant

    IV.   ABOUT PHOTO VOLTAIC SYSTEMS AND                         The basic equation (1) of the pv cell does not represent the
               MPPT ALGORITHM                                     I-V characteristic of a practical PV array. Practical arrays
                                                                  are composed of several connected PV cells and the
A photovoltaic (PV) system directly converts sunlight into        observation of the characteristic at the terminals of the PV
electricity. The basic device of a PV system is the PV cell.      array requires the inclusion of additional parameters to the
Cells may be grouped to form panels or arrays. The voltage        basic equation.

                                                                            ���� = ������������ − �exp ����� +                 � − 1� −
                                                                                                            ������������              ����+������������
and current available at the terminals of a PV device may

                                                                                                           ������������                ���� ����
directly feed small loads such as lighting systems and dc
motors. [7] A photovoltaic cell is basically a semiconductor                                                                                (15)


                                                                                               �������� = ����������������/����
diode whose p–n junction is exposed to light. Photovoltaic        Where
cells are made of several types of semiconductors using
different manufacturing processes. The incidence of light on




    September Issue                                      Page 31 of 132                                                     ISSN 2229 5216
                                                                        International Journal of Advances in Science and Technology,
                                                                                                                   Vol. 5, No.3, 2012

Is the thermal voltage of the array with Ns cells connected
in series. Cells connected in series provide greater output
voltages. The I-V characteristic of a practical PV cell with
maximum power point (MPP), Short circuit current (Isc)
and Open circuit voltage (Voc) is shown in Fig. 8. The MPP
represents the point at which maximum power is obtained.




          Fig. 8. I-V Characteristic of Practical PV Module
                                                                                   Fig. 10 Output Voltage ,Input Voltage, Duty cycle
Vmp and Imp are voltage and current at MPP respectively.
The output from PV cell is not the same throughout the day;               Fig 10 shows the Output voltage & input voltage and duty
it varies with varying temperature and insulation (amount of              cycle of the proposed switched inductor multilevel boost
radiation). Hence with varying temperature and insolation                 converter.
maximum power should be tracked so as to achieve the
efficient operation of PV system.


     V.     MATLAB/SIMULINK MODELLING AND
               SIMULATION RESULTS
            Here the simulation is carried out by three cases
1. Proposed switched inductor multilevel boost converter
2. Closed loop operation of proposed switched inductor
multilevel boost converter 3. Implementation of proposed
switched inductor multilevel boost converter by using PV
arrays applied to grid.

   Case 1: Proposed switched inductor multilevel boost                                    Fig .11. Input Current , Duty Cycle
converter:
                                                                          Fig 11 shows the Input Current & Duty Cycle of the
                                                                          proposed switched inductor multilevel boost converter.




      Fig.9. Matlab/Simulink modeling of proposed switched inductor
                      multilevel boost converter

   Fig.9 Shows the Matlab/Simulink modeling of proposed
switched inductor multilevel boost converter.
                                                                                             Fig.12. Voltage across switch




    September Issue                                              Page 32 of 132                                          ISSN 2229 5216
                                                                          International Journal of Advances in Science and Technology,
                                                                                                                     Vol. 5, No.3, 2012

Case 2:. Closed loop operation of proposed switched                         Fig 15 shows the Matlab/Simulink modeling of proposed
inductor multilevel boost converter                                         switched inductor multilevel boost converter by using PV
                                                                            arrays applied to grid.




                                                                                                Fig.16. Output Voltage
 Fig.13. Matlab/Simulink modeling of Closed loop operation of proposed
              switched inductor multilevel boost converter




 Fig.14. Output Voltage of Closed loop operation of proposed switched                       Fig.17. Inverter Output Voltage
                  inductor multilevel boost converter                       Fig 16, 17 shows the converter output voltage and output
                                                                            voltage of the inverter; we convert DC Voltage to AC by
Case 3: Implementation of proposed switched inductor                        using Interfacing Inverter and applied to Grid.
multilevel boost converter by using PV arrays applied to
grid.




                                                                                                 Fig.18. Grid Voltage
    Fig.15. Matlab/Simulink modeling of proposed switched inductor
      multilevel boost converter by using PV arrays applied to grid.




    September Issue                                                Page 33 of 132                                        ISSN 2229 5216
                                                                              International Journal of Advances in Science and Technology,
                                                                                                                         Vol. 5, No.3, 2012

                       V CONCLUSION                                                                    AUTHORS PROFILE
This paper proposed a new dc-dc converter topology. The                                           P GANESH KUMAR received his B.Tech degree
major advantages for this topology are high boosting ratio                                        from J.N.T.University, Hyderabad in the year 2009.
without using transformer. The voltage stress on the switch                                       At present he is pursuing his M.Tech degree
is smaller than the voltage stress on the switch in                                               Gudlavalleru Engineering College, Gudlavalleru, with
                                                                                                  the specialization of Power Electronics & Electrical
conventional boost converter. Also the efficiency of this                                         Drives. His areas of interest are Electrical Machines
converter has been found that is large and the output voltage                                     and Power Electronics, Electrical Circuits.
can be increased by increasing a level of this topology by
increasing a number of capacitors and diodes without
changing the main circuit and same proposed converter is
applied to Grid by using interfacing inverter.

                                                                                                 BALAJI GUTTA has received his B.Tech degree
                             REFERENCES                                                          from Gudlavalleru Engineering college, Gudlavalleru
                                                                                                 under J.N.T.University, Hyderabad in the year 2002.
[1] “Power Electronics Handbook” M.H. Rashid, Academic Press,                                    M.Tech degree with the specialization of Electrical
2001.                                                                                            Drives and Control from Pondicherry Engineering
                                                                                                 College in the year 2006. At present he is working as
[2] D. Maksimovic, and S. Cuk, "Switching converters with wide DC                                an Assistant Professor in Gudlavalleru Engineering
conversion range, " IEEE Transactions on Power Electronics, Vol. 6, pp.                          college, Gudlavalleru. His areas of interest are
149-157, Jan. 1991.                                                            Advanced Control Systems, Nonlinear control Systems, Control Systems,
                                                                               Network Analysis, Electrical Machines and Power Electronics.
[3] V. Paceco, A. Nascimento, V. Farias, J. Viera, L. Freitas, "A quadratic
buck converter with lossless commutation", IEEE Transactions on
Industrial Electronics, Vol. 47, pp. 264-271, Apr. 2001.

[4] Boris Axelrod, Yefim Berkovich, and Adrian Ioinovici “Switched
Capacitor/Switched Inductor Structures for Getting Transformerless Hybrid
DC–DC PWM Converters” IEEE Transactions on circuits and systems-I,
Regular papers, Vol.. 55, NO. 2, March 2008.

[5] Julio C. Rosas-Caro, Juan M. Ramírez, Pedro Martín García-Vite
"Novel DC-DC Multilevel Boost Converter." Proceeding of IEEE Power
Electronics Specialists Conference, 2008.

[6] Mahrous El-Sayed Ahmed, Mostafa Mousa, Mohamed Orabi
“Development of High Gain and Efficiency Photovoltaic System Using
Multilevel Boost Converter Topology” 2nd International Symposium on
Power Electronics for Distributed Generation Systems (PEDG2010).

[7] www.powersimtech.com.




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