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International Conference on Computing Technologies (ICONCT’17)

Organized by Department of Computer Science and Engineering & Information Technology 80

Investigation of High Gain DC-DC Converter Fed by

PV Source with Secondary Storage System Employing

Improved Incremental Conductance Algorithm based

MPPT Technique

A.Moshina Ahamed1,Dr.S.EdwardRajanand Dr.R.Pon Vengatesh

3

1 PG scholar,

2 Professor,

3 Assistant Professor (Sr. Grade),

Department of Electrical and Electronics Engineering,

Mepco Schlenk Engineering College (Autonomous), Sivakasi, Tamil Nadu, India.

Email: [email protected]; [email protected]; [email protected]

Abstract- Photovoltaic (PV) self consumption is becoming an

important aspect of storing and deferring energy generated from

distributed solar energy systems. In this paper, a novel high-gain

DC - DC converter is proposed for extraction of maximum power

from the PV panels. The proposed converter utilizes voltage

doublers to achieve high step-up voltage gain and due to the

clamping of voltage, the voltage stress on the switch is reduced

which improves the efficiency of the system. Reduced reverse

recovery of diodes, high voltage gain, and less duty cycle operation

are the important features of this proposed converter. The

proposed high gain DC-DC converter is feasibly used for low

input- voltage PV applications and tracking of PV module’s MPP

(Maximum Power Point) is challenging due to varying climatic

conditions. Improved Incremental Conductance (IIC) based

Maximum Power Point Tracking (MPPT) technique is

incorporated to track MPP from the PV system under different

operating conditions using Matlab-Simulink and the results has

been presented. Moreover, the float charging technique has been

adopted for charging secondary Lead acid battery in standalone

PV system applications.

Index Terms-PV System, High Gain DC-DC Converter, Maximum

Power Point Tracking, Improved Incremental Conductance

Algorithm, Lead Acid Battery.

I. INTRODUCTION

The problem of exhaustion of fossil energy reserves

and the environmental pollution has been resolved by the

development of “green power” generation.From the various

renewable energy sources, PV system represent one of the most

efficient and effective alternative sources for many applications,

such as uninterruptible power supplies, household electrical

appliances,and hybrid electric vehicles, etc.In general, the solar

cell stacks gives the output voltage varied from 24 to 40 V

depending on the output power. The input of the dc–ac inverter

requires a high DC bus voltage (380–400 V) in order to obtain

AC bus voltage (220V). Therefore, a high gain DC–

DCconverter is needed to raise the low voltage at the PV panel

into the high voltage at the dc bus.The proposed system consists

of PV panel connected to the DC load through the intermediate

DC–DC converter power stages as shown in Fig.1.

Fig.1. Solar Power generation system with high gain converter

In order to convert low PV panel voltage into the high

DC voltage [1], [2], a DC-DC converter with a high voltage gain

is necessary. In general, a conventional boost converter can be

utilized to provide a high voltage gain with a large duty ratio.

To increase the steady state voltage gain, the converter is

proposed in [2] and [3] uses Voltage Multiplier Cells (VMCs) that

comprise of diodes and capacitors. It results reduced conversion

efficiency due to the requirement of more number of components.

The work proposed in [4] uses the phase-shifted full-bridge

transformer. It increases the turn’s ratio of the transformer for

achieving the required high voltage gain. However, the output-

diode voltage stress is much higher than the output voltage and

more input electrolytic capacitors are required to reduce the large

input current ripple.Due to the constraints of the equivalent series

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resistance of inductors and capacitors, the losses of power

switches and diodes, and the reverse-recovery problem of diodes,

the conversion efficiency and the voltage gain are reduced. Hence,

to achieve high efficiency and high voltage gain, a high gain DC-

DC converter with moderate duty ratio is very important for a

solar energy conversion system.

II. MODELING OF THE PROPOSED CONVERTER

The output voltage of the intermediate DC-DC converter

should be high enough to generate the required dc-link

voltage.Hence, a high-voltage gain dc–dc converter is necessary to

combine the low-voltage PV panels to the distribution system.

Achieving higher voltage gains result the magnitude of the current

drawn from PV side is high, and hence, the converter operates

most of the times in continuous current mode (CCM). The basic

circuit diagram of the proposed single switch high gain DC-DC

converter is shown in Fig 2.

Fig.2.Circuit configuration of Proposed high gain DC-DC converter

The filter capacitor C0 and Resistance, R together form

a first order low pass output filter, which reduces the ripple

voltage below a specified level.

A. Operational Principle

The operating modes are described as follows:

Mode 1 (t0−t1): When the switch is ON

At t = t0, Ds1, Ds3and D2 are turned on, and D1 and D2 are turned

off. Fig 4(a) shows the current-flow path of the proposed

converter. In this interval, the inductors Ls1 and Ls2 are charged

from the dc input voltage and the energy is transferred to C0 and

the load. The inductor L1 charged from C1.The energy stored in

Ls1, Ls2 is released to C1 and the energy stored in L1 is released to

C0. At t = t1, iDs1, iDs3, and iD2 are equal to zero. This mode is

ended at t = t1 when S is turned off.

Mode 3 (t2−t3): When the switch is OFF

At t = t1, switch S is turned off.Ds2, D1, and D0 are turned on, and

Ds1, Ds3, and D2 are turned off. Fig 4(b) shows the current-flow

path of the proposed converter in this mode. In this interval the

energy stored in Ls1 and Ls2are released to capacitor C1.

Moreover, the energy stored in L1is released to C0 via D0. This

mode is ended at t = t2 when iC1 reaches constant.

Mode 3 (t2−t3): When the switch is OFF

At t = t2, switch S is kept turned off.Ds2, and D1 are turned

on, and Ds1, Ds3, D0 and D2 are turned off. Fig 4(c) illustrates the

current-flow path of the proposed converter in this mode. In this

interval the energies of input voltage source stored in Ls1 and

Ls2are released to capacitor C1. The load energy is supplied by

the output capacitor C0. The voltage across the switch is

increased linearly.During CCM operation,using volt–second

balance on inductors Ls1, Ls2, and L1, the following equations are

obtained:

0)1(2

2 1

DVV

DV cinin

…(1)

0)1()( 11 DVVDV Occ…(2)

From the equations (1) and (2), the steady state voltage gain

of the proposed converter can be written as,

2)1(

31

D

D

V

VGainVoltage

in

O

…(3)

(a)

(b)



(c)

Fig.4. Current flow path of the operating modes for CCM operation. (a)

Mode 1. (b) Mode 2. (c) Mode 3.

Fig.3. Steady state operating waveforms of high gain DC –

DC Converter in one switching period

The typical key waveforms under CCM operation in one

switching period is illustrated in Fig 3.The steady-state voltage

gain of the proposed high-gain PV converter is plotted against

duty cycle and compared with the some of the recently reported

converters like conventional boost, non isolated boost, high

step-upconverters as shown in Fig.5.It is clear that, for a given

duty cycle, the proposed high-gain converter topology provides

higher gain when compared to other topologies.

Fig.5. Steady state voltage gain versus duty ratio of different converters.

B. Simulation results of high gain DC-DCconverter

In this paper, MATLAB/Simulink is taken as the

platform for the design and performance comparison of

proposed system. MATLAB/Simulink results for high gain DC-

DC converter is presented in Fig 6.The respective waveforms

are shown in Fig 7.



Fig.6. Matlab-Simulink model of high gain DC-DC converter

Fig.7. Simulation response of input and output waveforms of high gain DC-DC converter

III. MODELING OF PV SYSTEM `

Generally, the Solar PV system uses sun tracking

system to enhance the performance and involves an integrated

battery solution, in which the cost of storage devices are

expected to depreciated over years. So it is necessary to build an

electrically equivalent model [6],[7] to understand the

electronicbehavior of the solar cell. The current produced by the

solar cell is given by,

1

akT

qVexpIII OPH

…(4)

PV array can be formed by connecting PV modules in

series and parallel to obtain the required power in terms of



voltage and current as shown in Fig 8. The PV arrays are

provided with a uniform insolation of G = 1000W/m2 and at

standard temperature of 25oC for all the interconnected modules

of PV array.

Fig.8. Matlab-Simulink model of PV array under uniforminsolation

Fig.9.I-V and P-V characteristics of PV array under partially shaded

conditions

The performance of PV array under partial shading

condition with two different shading patterns has been analyzed.

The shading pattern-1 is created by providing the first row of

the string with insolation of 1000W/m2, the next row with

insolation of 800W/m2. The shading pattern-2 is created by

providing the first row of the string with insolation of

1000W/m2, the next row with insolation of 600W/m

2. The PV

characteristics curves for shading patterns are plotted in Fig 9.

III. MPPT CONTROL TECHNIQUES

A. I&C Algorithm

In incremental conductance method, the incremental

conductance (ΔI/ ΔV) and the array conductance (I / V) are

compared to determine the maximum power. If both are same,

the output voltage is the maximum power point voltage.Finally,

this voltage is sustained by the controller until the irradiation

changes and the process is repeated. This method provides

sufficiently accurate maximum power point under the uniform

solar irradiation conditions. Under PSC, PV modules belonging

to the same string experience different insolation. The resulting

P-V characteristics curve exhibits multiple peaks. The presence

of multiple peaks reduces the effectiveness of the incremental

conductance algorithm, which assumes a single MPP on the P-

V curve. This algorithm is slightly more complex and robust.

B. IIC Algorithm

To overcome the demerits associated with the traditional

I&C algorithm, an Improved Incremental Conductance(IIC)

algorithm is proposed. This proposed algorithm lessens the

complexities associated with the generic algorithms. Fig.

10shows the mechanism of operation of IIC algorithm using P-

V curve of solar system.

Fig.10. Description of IIC algorithm using P – V curve

The IIC algorithm is implemented to divide the P-V

characteristic into three areas. Area 1 is from 0 to 70% of Voc.

Area 2 is from 70%to 80% of Voc. Area 3 is from 80%to

100%Voc. Area 2 is the area including the MPP.



Fig.11. Flowchart for IIC algorithm

The flowchart of the proposed IIC algorithm is shown in Fig.

11.The MATLAB/Simulink results for proposed converter fed

by PV source with IIC algorithm is presented in Fig 12.

888

Fig.12. Matlab-Simulink model of a PV array interfaced with the proposed converter under PSC with IIC MPPT algorithm



Fig.13. Simulation response of input and output waveforms of high gain DC-DC converter with PV source

Table.1. Comparative analysis of I&C and IIC algorithm for MPPT of

PV array under PSC

Shading on

PV panel Pattern I Pattern II

MPPT

controller I&C IIC I&C IIC

Vin (V) 58.64 44.94

Iin (A) 3.02 3.085 2.294 2.343

Pin (W) 177.1 180.9 103.1 105.3

D (%) 36 42 38 40

VO (V) 337.3 337.2 256.1 256

IO (A) 0.503 0.518 0.382 0.393

PO (W) 169.8 174.9 97.88 100.8

η (%) 95.86 96.68 94.94 95.76

The respective waveforms are shown in Fig 13.The

tracked values of voltage, current and power using the two

approaches (Shading Pattern I and Shading Pattern II) is

tabulated in Table.1, it is inferred that the proposed method

tracks the maximum value of power with less powerloss.

Hence efficiency of the system improved.

IV. SECONDARY STORAGE SYSTEM

The excess energy produced by the PV array during the day time

can be stored in batteries and it can be supplied to electrical loads

during the night and periods of cloudy weather as needed. In

order to protect the battery from overcharge and over discharge,

a battery charge controller is necessary.

A. Charging technique

The function of the proposed control logic shown in Fig

14 is described below. Initially the discharged battery terminal

voltage is compared to the trickle charge voltage threshold at the

beginning of the charging process. If V <VTrickle then the trickle

charging stage is enabled. If this condition is true then the upper

case is enabled and if this is false then the next switch condition

comes into action. The PI controller is designed in such a manner

that it minimizes the error between the actual and the

desired/reference value of charging current and according to that

PWM signal is given to the dc-dc buck converter. The buck

converter then supplies the preset trickle current to the battery.

The trickle charge current reference is set to C/10 amperes where

C isthe battery capacity in Ampere-hour (Ah).

Once the battery voltage reaches VTrickle then the bulk

charging stage is enabled. In this stage, the battery is charged by a

higher current IBulk until the battery voltage is less than its

overvoltage threshold VOC. Likewise the previous condition,

PWM operation is performed to give required pulse to the

converter. The converter then supplies constant current IBulk to the

battery. The battery voltage increases rapidly in this charging

stage because of high charging current and the IBulk is supplied to



the battery until the battery voltage reaches the overvoltage limit

VOC specified as 14.4V for a 12V lead acid battery. Once the

battery voltage reaches the overvoltage threshold VOC then the

charge controller changes its mode of charging from constant

current to constant voltage mode called float charging stage.The

third switch condition comes into operation when the second

switch condition fails.

Fig.14. Control logic for the three stage charge control algorithm

Fig.15.Matlab-Simulink model of PV array interfaced with proposed converter with battery charge controller

If this condition is true then the voltage across the

battery terminal is maintained at VOC and the battery takes

charging current in a decreasing fashion. This VOC is

maintained until the battery charging current goes down to a

lower threshold value IFloat. This IFloat threshold value is set as

C/100. When the battery charging current goes below the

threshold value of IFloat, then the PI controller sends

low(Zero)signal to the converter to terminate the charging

process. The MATLAB/Simulink model of PV array



interfaced with proposed converter with battery charge

controller and the response of battery such as SOC, Voltage

and Current is shown in Fig 15 and Fig 16 respectively.

Fig.16. Simulation response of battery charging

IV CONCLUSION

In this research paper, a novel high gain DC-DC power

converter circuit has been investigated for PV system under

different operating conditions by employing IIC algorithm

based MPPT scheme using Matlab-simulink environment. The

voltage gain characteristics have been studied for various duty

cycles. The obtained result shows that, for the same duty cycle

the voltage gain of this converter is high as compared to the

conventional boost converter. This converter topology

promotes high gain for photovoltaic applications and it

increases the voltagewithout using high frequency transformer

also which reduces the switching losses. Moreover, the power

converter interfaced with the PV system are analyzed by

employing I&C and IIC techniques and the simulated results

showed that, the IIC MPPT provides better tracking and

extracts significant amount of solar energy from a PV module

than I&C algorithm under all operating conditions. The

standalone PV system is also studied along with Lead acid

battery for storage purpose and it is used during low

irradiation, night times.

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