A Project Report on

“PHOTOVOLTAIC CHARGE CONTROLLER”

Submitted for partial fulfillment of requirement of award of

BACHELOR OF TECHNOLOGY

Degree

In

Electrical & Electronics Engineering

By

Akanksha Roll No. 0906321008

Prashant Verma Roll No. 0906321068

Sukriti Ranjan Rao Roll No. 0906321110

Avinav Prince Roll No. 0906321027

SESSION: 2012-13

G.L.A. INSTITUTE OF TECHNOLOGY AND MANAGEMENT, MATHURA

CERTIFICATE

This is to certify that the project entitled “Photovoltaic Charge Controller” is

the bonafide work of Akanksha, Prashant Verma, Sukriti Ranjan Rao, and Avinav

Prince submitted in partial fulfillment of the requirements for the award of the

degree of Bachelor of Technology (B.Tech.) in Electrical and Electronics (EN) by

GBTU, Lucknow, U.P. during the academic year 2012-2013.

Signature

(Mr. Subhash Chandra)

Project Supervisor

ACKNOWLEDGEMENT

We would like to express our gratitude towards all the people who have

contributed their precious time and efforts to help us in completing this project,

without whom it would not have been possible for us to understand and analyze

the project.

We would like to thank Mr. Subhash Chandra, Department of Electrical

Engineering, and our Project Supervisor, for his guidance, support, motivation and

encouragement throughout the period this work was carried out. His readiness for

consultation at all times, his educative comments, his concern and assistance have

been invaluable.

We are also grateful to Dr. S. Basu, Professor and Head, Department of Electrical

and Electronics Engineering, for providing the necessary facilities in the

department.

We would also like to thank Mr. Sanjay Maurya, Department of Electrical and

Electronics Engineering, our Project Incharge, for consultation and support

throughout the length of the project.

TABLE OF CONTENTS

CHAPTER PAGE

TITLE i

CERTIFICATE ii

ACKNOWLEDGEMENT iii

TABLE OF CONTENT iv

LIST OF TABLES vii

LIST OF FIGURES viii

1. INTRODUCTION

1.1 Background 1

1.2 Objectives 2

1.3 Scope of Project 2

2. LITERATURE REVIEW

2.1 Need of Renewable Energy. 3

2.2 Different Sources of Renewable Energy 3

2.3 Renewable Energy Trends across the globe 5

2.4 Why Solar Energy? 5

2.5 Recent Data on Solar Power in India 5

3. PHOTOVOLTAIC POWER TECHNOLOGY

3.1 Photovoltaic Cell 6

3.2 PV Module 8

3.3 PV Modelling 8

3.4 PV Charge Controller 8

4. DC-DC Converter

4.1 Buck (Step-Down) Converter 11

4.1.1 Basic Modes of Operation Buck Converter 12

4.1.2 Simulink Model of Buck Converter 15

4.1.3 Output Waveform Scope 16

4.2. Boost (Step-Up) Converter 17

4.2.1 Basic Modes of Operation Boost Converter 18

4.2.2 Simulink Model of Boost Converter 21

4.2.3 Output Waveform Scope 22

4.3 Mathematical analysis of Boost Converter 23

4.4 Variation in Duty Cycle for constant output Voltage 23

4.5 Variation between Input Voltage and Duty Cycle 24

4.6 Matlab Script Code for Boost converter 25

4.7 Case Study 26

4.8 Pulse Width Modulation (PWM) 27

5. BUCK-BOOST CONVERTER

5.1 Introduction 28

5.2 Modes of Operation Buck-Boost Converter 29

5.2.1 Simulink Model of Buck-Boost Converter 32

5.2.2 PWM Controller Subsystem 33

5.2.3 Output Waveform Scope 34

6. COMPONENTS

6.1 Introduction to MATLAB™ and SIMULINK™ 35

6.2 Components Used 38

6.1.1 MOSFET 38

6.1.2 Inductor 39

6.1.3 Capacitor 40

6.1.4 Diode 41

6.1.5 Pulse Generator 42

6.1.6 Resistor 43

6.1.7 Repeating Sequence 44

6.1.8 Scope 44

6.1.9 Power GUI 45

REFERENCES 46

List of Table:

4 (i) Boost Converter Output for Constant Duty Cycle

4 (ii) Boost Converter Output for Constant Input Voltage

4 (iii) Graph showing variation between Duty Cycle and Input Voltage

4 (iv) RLC values for 8-24V

List of Figures:

4.a. Circuit Diagram of Buck Converter

4.b. Buck Converter in ON state

4.c. Buck Converter in OFF state

4.d. Simulink model of Buck Converter

4.e. Scope of Buck Converter

4.f. Circuit Diagram of Boost Converter

4.g. Boost Converter in ON state

4.h. Boost Converter in OFF state

4.i. Boost Converter in OFF state (Both transistor and diode OFF)

4.d. Simulink model of Boost Converter

4.e. Scope of Boost Converter

1

Chapter 1

Introduction

1.1 Background

Photovoltaic or in short term PV is one of the renewable energy resources that

recently has become broader in nowadays technology. PV has many benefits

especially in environmental, economic and social. In general, a PV system

consists of a PV array which converts sunlight to direct-current electricity, a

control system which regulates battery charging and operation of the load, energy

storage in the form of secondary batteries and loads or appliances. A charge

controller is one of functional and reliable major components in PV systems. A

good, solid and reliable PV charge controller is a key component of any PV

battery charging system to achieve low cost and the benefit that user can get from

it.

1.a. Block diagram of PV system

The main function of a charge controller in a PV system is to regulate the

voltage and current from PV solar panels into a rechargeable battery. The

minimum function of a PV charge controller is to disconnect the array when the

battery is fully charged and keep the battery fully charged without damage. A

charge controller is important to prevent battery overcharging, excessive

discharging, reverse current flow at night and to protect the life of the batteries in

a PV system. A power electronics circuit is used in a PV charge controller to get

highest efficiency, availability and reliability. The use of power electronics

circuits such as various dc to dc converters topologies like buck converter, boost

Solar

Energy

Photovoltaic

cell

Photovoltaic

Charge

Controller

Battery

System

2

converter, buck-boost converter and others converter topology as power

conditioning circuitry to provide a desired current to charge battery effectively.

1.2 OBJECTIVES

(i) To design Photovoltaic (PV) Charge Controller by using Pulse Width

Modulation as a switching controller.

(ii) To maintain constant output voltage for the variable input voltage of the

Photovoltaic Cell and to charge a battery.

1.3 SCOPE OF PROJECT

(i) The PV charge controller that designed in this project will be implement

Pulse Width Modulation (PWM) controller in it.

(ii) This project concentrates on DC-DC Converter.

(iii) This project will use PWM controller to control the voltage and current at

certain values that have been set which act as an input to the gate junction

of mosfets, which results in constant output voltage of this photovoltaic

charge controller.

3

Chapter 2

LITERATURE REVIEW

2.1 Need for Renewable Energy

Renewable energy is the energy which comes from natural resources such as

sunlight, wind, rain, tides and geothermal heat. These resources are renewable and

can be naturally replenished.

Many forms of energy that we have grown dependent on are from non-

renewable energy sources. This means that when the energy has been consumed,

the supply has gone and cannot be replaced. An example of this is coal. Coal is

known as a fossil fuel and is the largest source of energy for the generation of

electricity worldwide. When coal has been mined and burnt, it cannot be replaced.

Finding alternative energy sources, ideally from renewable sources, will decrease

our dependency on fossil fuels and other non-renewable energy sources.

Therefore, for all practical purposes, renewable resources can be considered

to be inexhaustible, unlike dwindling conventional fossil fuels.

2.2 Different sources of Renewable Energy

2.2.1 Wind power

Wind turbines can be used to harness the energy available in airflows. Current day

turbines range from around 600 kW to 5 MW of rated power. Since the power

output is a function of the cube of the wind speed, it increases rapidly with an

increase in available wind velocity. Recent advancements have led to aerofoil

wind turbines, which are more efficient due to a better aerodynamic structure.

4

2.2.2 Solar power

The tapping of solar energy owes its origins to the British astronomer John

Herschel who famously used a solar thermal collector box to cook food during an

expedition to Africa. Solar energy can be utilized in two major ways. Firstly, the

captured heat can be used as solar thermal energy, with applications in space

heating. Another alternative is the conversion of incident solar radiation to

electrical energy, which is the most usable form of energy. This can be achieved

with the help of solar photovoltaic cells or with concentrating solar power plants.

2.2.3 Small hydropower

Hydropower installations up to 10MW are considered as small hydropower and

counted as renewable energy sources. These involve converting the potential

energy of water stored in dams into usable electrical energy through the use of

water turbines. Run-of-the-river hydroelectricity aims to utilize the kinetic energy

of water without the need of building reservoirs or dams.

2.2.4 Biomass

Plants capture the energy of the sun through the process of photosynthesis. On

combustion, these plants release the trapped energy. This way, biomass works as

a natural battery to store the sun’s energy and yield it on requirement.

2.2.5 Geothermal

Geothermal energy is the thermal energy which is generated and stored [9] within

the layers of the Earth. The gradient thus developed gives rise to a continuous

conduction of heat from the core to the surface of the earth. This gradient can be

utilized to heat water to produce superheated steam and use it to run steam turbines

to generate electricity. The main disadvantage of geothermal energy is that it is

usually limited to regions near tectonic plate boundaries, though recent

advancements have led to the propagation of this technology.

5

2.3 Renewable Energy Trends across the Globe

Due to the increasing demand for the energy there are some methods that can be

used to store energy.

From sun, solar power is radiated it is energy and can be stored in a

From the movement of huge quantity of water a hydropower is come from it.

One way is geothermal power; in this way energy from hot water and steam

can be produced on earth’s surface.

Wind power is usually used by big turbines same as that of the windmills that

are roiled by the atmospheric winds.

Among these applications Solar Energy is the most efficient, easy and practical

method to be acceptable for the production of electricity.

2.4 Why Solar Energy?

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at

the upper atmosphere.Approximately 30% is reflected back to space while the rest

is absorbed by clouds, oceans and land masses.

2.5 Recent Data on Solar Power in India

Total development of Solar PV system in India has exceeded 1040 MW.

Under first phase of Jawahar lal Nehru National Solar Mission (JNNSM) to

be implemented between 1st april 2010 and 31st march 2013, 200MW

capacity equivalent off grid Solar PV systems and 7 million square meteres

solar thermal collector are to be installed in the country. As an feb 2011, the

achievement figures are 38.5MW for off grid PV system and 1.2 lakh

square meter solar thermal collecter area.

A 214 MW solar park was installed recently at Charanka (Gujarat).

By the end of 2011, a total of 67.4 GW had been installed, sufficient to

generate 85 TWh/year. And by end of 2012, the 100 GW installed capacity

milestone was achieved.

6

Chapter 3

Photovoltaic Power Technology

3.1 Photovoltaic Cell

A photovoltaic cell or photoelectric cell is a semiconductor device that converts

light to electrical energy by photovoltaic effect. If the energy of photon of light is

greater than the band gap then the electron is emitted and the flow of electrons

creates current.

However a photovoltaic cell is different from a photodiode. In a photodiode

light falls on n-channel of the semiconductor junction and gets converted into

current or voltage signal but a photovoltaic cell is always forward biased.

The photovoltaic (pv) power technology uses semiconductor cells (wafers),

generally several square centimeters in size. The cell is basically a large area p-n

diode with the junction positioned close to the top surface. The cell converts the

sunlight into direct current electricity. Numerous cells are assembled in a module

to generate required power..

Typically a solar cell can be modelled by a current source and an inverted

diode connected in parallel to it. It has its own series and parallel resistance.

Series resistance is due to hindrance in the path of flow of electrons from n to p

junction and parallel resistance is due to the leakage current.

3.a. Single diode model of a PV cell

7

Where I is the reverse saturation current of the diode, q is the electron charge, Vd

is the voltage across the diode, k is Boltzmann constant (1.38 * 10-19 ) J/K) and T

is the junction temperature in Kelvin (K)

3.b. I-V characteristics of PV cell

8

3.2 PV Module

Usually a number of PV modules are arranged in series and parallel to meet the

energy requirements. PV modules of different sizes are commercially available

(generally sized from60W to 170W). For example, a typical small scale

desalination plant requires a few thousand watts of power.

3.3 PV Modelling

A PV array consists of several photovoltaic cells in series and parallel

connections. Series connections are responsible for increasing the voltage of the

module whereas the parallel connection is responsible for increasing the current

in the array. Typically a solar cell can be modeled by a current source and an

inverted diode connected in parallel to it. It has its own series and parallel

resistance. Series resistance is due to hindrance in the path of flow of electrons

from n to p junction and parallel resistance is due to the leakage current.

The relationship between volts, amps, and watts. Solar panels are typically

marketed based on their peak power production, measured in watts.

Watts = Volts x Amps

2.4 Photovoltaic Charge Control

In general, a PV system consists of a PV array which converts sunlight to direct-

current electricity, a control system which regulates battery charging and

operation of the load, energy storage in the form of secondary batteries and loads

or appliances. A charge controller is one of functional and reliable major

components in PV systems. A good, solid and reliable PV charge controller is a

key component of any PV battery charging system to achieve low cost and the

benefit that user can get from it.

The main function of a charge controller in a PV system is to regulate the

voltage and current from PV solar panels into a rechargeable battery. The

minimum function of a PV charge controller is to disconnect the array when the

battery is fully charged and keep the battery fully charged without damage. A

charge controller is important to prevent battery overcharging, excessive

9

discharging, reverse current flow at night and to protect the life of the batteries in

a PV system. Efficiency, size, and cost are the primary advantages of switching

power converters when compared to linear converters. Switching power converter

efficiencies can run between 70-80%, whereas linear converters are usually 30%

efficient. These converters are generally either hard-switched PWM or soft-

switched resonant link types.

The hard-switched PWM converters operate with a fixed-frequency,

variable duty cycle. This type of signal is called Pulse Width Modulated signal

(PWM), depending on the duty cycle, they can operate in either continuous current

mode (CCM) or discontinuous current mode (DCM). If the current through the

output inductor never reaches zero then the converter operates in CCM; otherwise

DCM occurs.

The output voltage will be equal with the average value on the switching

cycle of the voltage applied at the output filter. Due to the losses on the ON or

OFF state of the ideal transistor are zero, the theoretical efficiency of the switching

mode converters is up to 100%. But, considering the real switches, with parasitic

elements, the efficiency will be a little bit lower, but higher than linear regulators.

Another advantage of switching mode converters consist in the possibility

to use the same components but in other topology in order to obtain different

values of the output voltages: positive or negative, lower or higher than input

voltage.

There are various analysis methods of DC-DC converters. While demands

for portable power electronics have grown significantly during the last a few

years, end users are more concerned about the battery run-time. Extending the

battery run-time becomes the top priority for the system designers. This project

overviews three commonly used DC-DC conversion topologies suitable for

battery operated systems:

Buck converter,

Boost converter,

Buck-Boost converter.

In this approach, the differential equations that describe the inductor current

and capacitor voltage are determined and are solved according with the boundary

10

conditions of the switching periods. The values of currents and voltages at the end

of a period become initial conditions for the next switching period. This method

is very accurate and produces a set of equations that require extensive

computation.

11

Chapter 4

DC-DC Converters

4.1 BUCK (Step-Down) CONVERTER

A buck converter is called a step-down DC to DC converter because the

output voltage is less than the input. Its design is similar to the step-up boost

converter, and like the boost converter it is a switched-mode power supply that

uses two switches (a transistor and a diode) and an inductor and a capacitor.

Most buck converters are designed for continuous-current mode operation

compared to the discontinuous-current mode operation. The continuous-current

mode operation is characterized by inductor current remains positive throughout

the switching period. Conversely, the discontinuous-current mode operation is

characterized by inductor current returning to zero during each period.

The figure below shows the basic of buck converter circuit. The switches

alternates between connecting the inductor to source voltage to store energy in the

inductor and discharging the inductor into the load with at a rate of PWM

switching frequency.

The output that results is a regulated voltage of smaller magnitude than

input voltage. The converter operation will be analyzed function of switches state.

4.a. Circuit diagram of Buck Converter

12

4.1.1 Basic modes of Operation of Buck Converter:

A) THE FIRST TIME INTERVAL: Transistor is in ON state and diode is OFF.

During this time period, corresponding with duty cycle of PWM driving signal,

the equivalent diagram of the circuit is presented below:

4.b. Buck converter in ON state

When the switch is in ON state, diode become as reversed biased and the inductor

will deliver current and switch conducts inductor current. With the voltage (Vin -

Vo) across the inductor, the current rises linearly (current changes, ΔiL). The

current through the inductor increase, as the source voltage would be greater then

the output voltage and capacitor current may be in either direction depending on

the inductor current and load current.

When the current in inductor increase, the energy stored also increased. In

this state, the inductor acquires energy. Capacitor will provides smooth out of

inductor current changes into a stable voltage at output voltage and it’s big enough

such that V out doesn’t change significantly during one switching cycle.

For this equivalent circuit will write the equations that describe the

converter operation:

13

𝑑𝑢𝑜

𝑑𝑡 𝑖𝐿

𝑢𝑜

𝑅

𝐶;

𝑑𝑖𝐿

𝑑𝑡 𝐸

𝑢𝑜

𝐿;

B) THE SECOND TIME PERIOD: The transistor is OFF and diode is ON.

In the moment when the transistor switch in OFF state, the voltage across the

inductor will maintains current to load. Because of inductive energy storage, iL

will continues to flow. While inductor releases current storage, it will flow to the

load and provides voltage to the circuit. The diode is forward biased. The current

flow through the diode which is inductor voltage is equal with negative output

voltage. The equivalent diagram of the circuit is presented below:

4.c. Buck Converter in OFF state

For this operation period, the output voltage u0 and the current through the

inductor iL satisfy the following equations:

14

𝑑𝑢𝑜

𝑑𝑡 𝑖𝐿

𝑢𝑜

𝑅

𝐶;

𝑑𝑖𝐿

𝑑𝑡

𝑢𝑜

𝐿;

15

4.1.2 Simulink Model of Buck Converter:

4.d. Simulink Model of Buck Converter

16

4.1.3 Output Waveform Scope :

4.e. Scope of Buck Converter

17

4.2 BOOST (Step-Up) CONVERTER

The boost (or step-up converter), contains a capacitor and an inductor with role of

energy storing, and two complementary switches. In the case of the boost

converter, the output voltage is higher than the input voltage. The switches are

alternately opened and closed with at a rate of PWM switching frequency. As long

as transistor is ON, the diode is OFF, being reversed biased. The input voltage,

applied directly to inductance L, determines a linear rising current. When

transistor is OFF, the load is supplied by both input source and LC filter. The

output that results is a regulated voltage of higher magnitude than input voltage.

The converter operation will be analyzed according with the switches states.

4.f. Circuit Diagram of Boost Converter.

‘

18

4.2.1 Modes of Operation

A) THE FIRST TIME INTERVAL: The transistor is in ON state and

diode is OFF.

During this time period, corresponding with duty cycle of PWM driving signal,

the equivalent diagram of the circuit is presented below. In this time period the

inductance L store energy.

3.g. Boost Converter in ON State

For this operation period, the output voltage u0 and the current through the

inductor iL satisfies the following equations:

𝑑𝑢𝑜

𝑑𝑡

𝑢𝑜

𝑅𝐶;

𝑑𝑖𝐿

𝑑𝑡

𝐸

𝐿;

19

B) THE SECOND TIME PERIOD: The transistor is OFF and diode is

ON.

In the moment when the transistor switch in OFF state, the voltage across the

inductor will change the polarity and diode will switch in ON state. The equivalent

diagram of converter during this period is shown in the bellow figure:

4.h. Boost Converter in OFF state

For this operation period, the output voltage u0 and the current through the

inductor iL satisfy the following equations:

𝑑𝑢𝑜

𝑑𝑡 𝑖𝐿

𝑢𝑜

𝑅

𝐶;

𝑑𝑖𝐿

𝑑𝑡 𝐸

𝑢𝑜

𝐿;

20

C) THE THIRD OPERATION MODE: The both transistor and diode

are OFF. If the inductor current becomes zero before ending the diode conduction period,

both the transistor and the diode will be in OFF state. Due to the diode current

becomes zero, the diode will naturally close, and the output capacitor will

discharge on the load. This operation regime is called discontinuous current mode.

The equivalent diagram of this operation regime is shown below:

4.i. Boost Converter in OFF state (both transistor and diode are OFF)

For this operation period, the output voltage u0 and the current through the

inductor iL can be calculated from the following equations:

𝑑𝑢𝑜

𝑑𝑡

𝑢𝑜

𝑅𝐶;

𝑑𝑖𝐿

𝑑𝑡 0;

21

4.2.2 Simulink Model of Boost Converter:

4.j. Simulink Model of Boost Converter.

22

4.2.3 Output Waveform Scope:

4.k. Scope of Boost Converter.

23

4.3 MATHEMATICAL ANALYSIS OF BOOST CONVERTER:

S.No Input Voltage Duty Cycle Output Voltage

1 10 85 12.86

2 12 85 15.43

3 14 85 18

4 16 85 20.57

5 18 85 23.14

6 20 85 25.71

7 22 85 28.28

3(i) Boost converter output for constant duty cycle

4.4 VARIATION IN DUTY CYCLE FOR CONSTANT OUTPUT

VOLTAGE

S.No. Input Voltage Duty Cycle Output Voltage

1 10 85.84 15

2 10.5 85.554 15

3 11 85.304 15

4 11.5 85.074 15

5 12 84.86 15

6 12.5 84.66 15

7 13 84.47 15

8 13.5 84.29 15

9 14 84.116 15

10 14.5 83.954 15

4 (ii) Boost Converter output for constant output

24

4.5 VARIATION BETWEEN INPUT VOLTAGE AND DUTY

CYCLE:

4(iii) Graph shoeing variation between duty cycle and input voltage

The above graph shows variation between Input Voltage and Duty Cycle. The

Negative Slope indicates that increase in input voltage results in decrease in duty

cycle.

83

83.5

84

84.5

85

85.5

86

10 10.5 11 11.5 12 12.5 13 13.5 14 14.5

Input Voltage

DU

TY C

YCLE

25

4.6 BOOST CONVERTER CODING (for user interface) :

clc;

Vin=input('enter the input voltage:');

Vout=input('enter the output voltage:');

I=input('enter the maximum output current:');

f=input('enter the switching frequency:');

D=1-(Vin/Vout);

di=I*D;

L=Vin/(f*di);

dv=0.5;

C=((I-di)*D)/(f*dv);

R=Vout/I;

disp('DUTY CYCLE:');

D=D*100;

D

disp('INDUCTOR VALUE:');

L

disp('CAPACITOR VALUE micro farad:');

C

disp('RESISTOR VALUE:');

R

26

4.7 CASE STUDY:

INPUT RANGE: 8-24V

OUTPUT VOLTAGE: 30V

Vin Vout R L C

8 30 15 0.1091 0.0156

10 30 15 0.1500 0.0178

12 30 15 0.2000 0.0192

14 30 15 0.2625 0.0199

16 30 15 0.3429 0.0199

18 30 15 0.4500 0.0192

20 30 15 0.6000 0.0178

22 30 15 0.8250 0.0178

24 30 15 1.2000 0.0156

4 (iv) R L C Values for 8-24 V

For constant values of

Resistance (R) = 12 Ω

Inductance (L) = 1 H

Capacitance (C) = 0.04 µF

Input Voltage (Vin) = 15 V

Output Voltage (Vout) = 30 V

Maximum output current (Imax) = 3 A

Switching frequency (f) = 50 Hz

27

4.8 Pulse Width Modulation (PWM)

Pulse Width Modulation (PWM) controls adjusts the duty ratio of the

switches as the input changes to produce a constant output voltage. The DC

voltage is converted to a square-wave signal, alternating between fully on and

zero. By controlling analog circuits digitally, system costs and power

consumption can be drastically reduced. In nowadays implementation, many

microcontrollers already include on-chip PWM controllers making

implementation easy. In a nutshell, PWM is a way of digitally encoding analog

signal levels.

PWM control can be used in two ways: voltage-mode and current-mode. In

voltage-mode control the output voltage increases and decreases as the duty ratio

increases and decreases. The output voltage is sensed and used for feedback. If it

has two-stage regulation, it will first hold the voltage to a safe maximum for the

battery to reach full charge. Then it will drop the voltage lower to sustain a "finish"

or “trickle" charge. Two-stage regulating is important for a system that may

experience many days or weeks of excess energy (or little use of energy). It

maintains a full charge but minimizes water loss and stress. The voltages at which

the controller changes the charge rate are called set points.

When determining the ideal set points, there is some compromise between

charging quickly before the sun goes down, and mildly overcharging the battery.

The determination of set points depends on the anticipated pattern of use, the type

of battery, and to some extent, the experience and philosophy of the system

designer or operator.

28

Chapter 5

BUCK BOOST CONVERTER

5.1 BUCK BOOST CONVERTER

A buck-boost converter provides an output voltage that may be less than or greater

than the input voltage hence the name „‟ buck-boost’’; the output voltage polarity

is opposite to that of the input voltage. This converter is also known as an

inverting regulator. The circuit arrangement of a buck-boost convertor is shown

in figure below:

5.a. Circuit Diagram of Buck-Boost Converter

The switches are alternately opened and closed with at a rate of PWM switching

frequency. As long as the transistor is ON, the diode is OFF, being reversed biased.

The input voltage, applied directly to inductance L, determines a linear rising

current. The capacitor is discharged on the load circuit. When the transistor is

OFF, the load is supplied by LC filter. The output that results is a regulated voltage

of smaller or higher magnitude than input voltage, depending on the value of duty

cycle, but it has a reverse polarity. The converter operation will be analyzed

according with the ON or OFF state of switches.

29

5.2 Modes of operation

Phase Mosfet 1 Mosfet 2 Operating modes

1 OFF OFF BUCK

2 OFF ON OFF

3 ON OFF BUCK-BOOST

4 ON ON BOOST

5(i) Modes of operation of Buck-Boost Converter

A) THE FIRST TIME INTERVAL: The transistor is in ON state and

diode is OFF.

During this time period, corresponding with duty cycle of PWM driving signal,

the equivalent diagram of the circuit is presented below. In this time period the

inductance L stores energy. The load current is assured by the output capacitor.

5.b. Buck Boost Converter in ON state.

For this operation period, the output voltage u0 and the current through the

inductor iL are given by the following equations system:

𝑑𝑢𝑜

𝑑𝑡

𝑢𝑜

𝑅𝐶;

30

𝑑𝑖𝐿

𝑑𝑡 𝐸;

B) THE SECOND TIME PERIOD: the transistor is OFF and diode is

ON.

In the moment when the transistor switch in OFF state, the voltage across the

inductor will change the polarity and diode will switch in ON state. The energy

stored in the inductor will supply the load. The equivalent diagram of converter

during this period is shown in the figure below:

5.c. Buck Boost Converter in OFF state.

For this operation period, the following equations for the output voltage u0 and the

current through the inductor iL can be written as:

𝑑𝑢𝑜

𝑑𝑡 𝑖𝐿

𝑢𝑜

𝑅

𝐶;

𝑑𝑖𝐿

𝑑𝑡

𝑢𝑜

𝐿;

31

C) THE THIRD OPERATION MODE: The both transistor and diode

are OFF.

If the inductor current becomes zero before ending the diode ON period, both the

transistor and the diode will be OFF. Due to the diode current becomes zero, the

diode will naturally close, and the output capacitor will discharge on the load.

This operation regime is called discontinuous current mode. The equivalent

diagram of this operation regime is shown below:

5.d. Buck-Boost Converter in OFF state (both transistor and diode are OFF)

For this operation mode, the output voltage u0 and the current through the inductor

il can be calculated from the following differential equations:

𝑑𝑢𝑜

𝑑𝑡

𝑢𝑜

𝑅𝐶;

𝑑𝑖𝐿

𝑑𝑡 0 ;

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5.2.1 Simulink Model of Buck-Boost Converter for PV array of 50-

200V output:

5.e. Simulink Model of Buck-Boost Converter

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5.2.2 PWM Controller Subsystem Simulink Diagram

5.f. Simulink Model of PWM Controller

34

5.2.3 Output Waveform Scope:

a) For Vin = 75 V Vout = 100.5 V

5.f. Scope of Buck-Boost Converter

35

Chapter 6

COMPONENTS

6.1 MATLAB® AND SIMULINK®

MATLAB® Version R2009a 7.8.0 (64 bit)

6.1.1 Overview of the MATLAB Environment

The MATLAB high-performance language for technical computing

integrates computation, visualization, and programming in an easy-to-use

environment where problems and solutions are expressed in familiar mathematical

notation. Typical uses include

Math and computation

Algorithm development

Data acquisition

Modeling, simulation, and prototyping

Data analysis, exploration, and visualization

Scientific and engineering graphics

Application development, including graphical user interface building

MATLAB is an interactive system whose basic data element is an array that

does not require dimensioning. It allows you to solve many technical computing

problems, especially those with matrix and vector formulations, in a fraction of

the time it would take to write a program in a scalar non-interactive language such

as C or FORTRAN.

The name MATLAB stands for matrix laboratory. MATLAB was originally

written to provide easy access to matrix software developed by the LINPACK and

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EISPACK projects. Today, MATLAB engines incorporate the LAPACK and

BLAS libraries, embedding the state of the art in software for matrix computation.

MATLAB has evolved over a period of years with input from many users.

In university environments, it is the standard instructional tool for introductory

and advanced courses in mathematics, engineering, and science. In industry,

MATLAB is the tool of choice for high-productivity research, development, and

analysis.

MATLAB features a family of add-on application-specific solutions called

toolboxes. Very important to most users of MATLAB, toolboxes allow you to

learn and apply specialized technology. Toolboxes are comprehensive collections

of MATLAB functions (M-files) that extend the MATLAB environment to solve

particular classes of problems. You can add on toolboxes for signal processing,

control systems, neural networks, fuzzy logic, wavelets, simulation, and many

other areas.

6.1.2 The MATLAB System

The MATLAB system consists of these main parts:

Desktop Tools and Development Environment

This part of MATLAB is the set of tools and facilities that help you use and

become more productive with MATLAB functions and files. Many of these tools

are graphical user interfaces. It includes: the MATLAB desktop and Command

Window, an editor and debugger, a code analyzer, browsers for viewing help, the

workspace, and files, and other tools.

Mathematical Function Library

This library is a vast collection of computational algorithms ranging from

elementary functions, like sum, sine, cosine, and complex arithmetic, to more

sophisticated functions like matrix inverse, matrix eigenvalues, Bessel functions,

and fast Fourier transforms.

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The Language

The MATLAB language is a high-level matrix/array language with control

flow statements, functions, data structures, input/output, and object-oriented

programming features. It allows both "programming in the small" to rapidly create

quick programs you do not intend to reuse. You can also do "programming in the

large" to create complex application programs intended for reuse.

Graphics

MATLAB has extensive facilities for displaying vectors and matrices as

graphs, as well as annotating and printing these graphs. It includes high-level

functions for two-dimensional and three-dimensional data visualization, image

processing, animation, and presentation graphics. It also includes low-level

functions that allow you to fully customize the appearance of graphics as well as

to build complete graphical user interfaces on your MATLAB applications.

External Interfaces

The external interfaces library allows you to write C and Fortran programs

that interact with MATLAB. It includes facilities for calling routines from

MATLAB (dynamic linking), for calling MATLAB as a computational engine,

and for reading and writing MAT-files.

6.2 SIMULINK®

Simulink® software models, simulates, and analyzes dynamic systems. It

enables you to pose a question about a system, model the system, and see what

happens.

With Simulink, you can easily build models from scratch, or modify

existing models to meet your needs. Simulink supports linear and nonlinear

systems, modeled in continuous time, sampled time, or a hybrid of the two.

Systems can also be multirate—having different parts that are sampled or updated

at different rates.

38

Thousands of scientists and engineers around the world use Simulink to model

and solve real problems in a variety of industries, including:

Aerospace and Defense

Automotive

Communications

Electronics and Signal Processing

Medical Instrumentation

6.3 COMPONENTS USED

6.3.1 MOSFET

6.a. MOSFET symbols in Simulink

The metal-oxide semiconductor field-effect transistor (MOSFET) is a

semiconductor device controllable by the gate signal (g > 0). The MOSFET device

is connected in parallel with an internal diode that turns on when the MOSFET

device is reverse biased (Vds < 0) and no gate signal is applied (g=0). The model

39

is simulated by an ideal switch controlled by a logical signal (g > 0 or g = 0), with

a diode connected in parallel.

The MOSFET device turns on when a positive signal is applied at the gate input

(g > 0) whether the drain-source voltage is positive or negative. If no signal is

applied at the gate input (g=0), only the internal diode conducts when voltage

exceeds its forward voltage Vf.

With a positive or negative current flowing through the device, the

MOSFET turns off when the gate input becomes 0. If the current I is negative and

flowing in the internal diode (no gate signal or g = 0), the switch turns off when

the current I becomes 0.

The on state voltage Vds varies

Vds = Ron*I when a positive signal is applied at the gate input.

Vds = Rd*I-Vf +Lon*dI/dt when the antiparallel diode is conducting (no

gate signal).

The Lon diode inductance is available only with the continuous model. For most

applications, Lon should be set to zero for both continuous and discrete models.

The MOSFET block also contains a series Rs-Cs snubber circuit that can

be connected in parallel with the MOSFET (between nodes d and s).

6.1.2 Inductor

An inductor (also choke, coil, or reactor) is a passive two-terminal electrical

component that stores energy in its magnetic field. For comparison,

a capacitor stores energy in an electric field, and a resistor does not store energy

but rather dissipates energy as heat.

Any conductor has inductance. An inductor is typically made of a wire or

other conductor wound into a coil, to increase the magnetic field. When the

current flowing through an inductor changes, a time-varying magnetic field is

created inside the coil, and a voltage is induced, according to Faraday’s law of

40

electromagnetic induction, which by Lenz's law opposes the change in current that

created it. Inductors are one of the basic components used in electronics where

current and voltage change with time, due to the ability of inductors to delay and

reshape alternating currents.

The effect of an inductor in a circuit is to oppose changes in current through it by

developing a voltage across it proportional to the rate of change of the current. An

ideal inductor would offer no resistance to a constant direct current; however,

only superconducting inductors have truly zero electrical resistance.

The relationship between the time-varying voltage v(t) across an inductor with

inductance L and the time-varying current i(t) passing through it is described by

the differential equation:

𝑡 𝐿𝑑𝑖 𝑡

𝑑𝑡

6.1.3 Capacitor

A capacitor (originally known as condenser) is a passive two-terminal electrical

component used to store energy in an electric field. The forms of practical

capacitors vary widely, but all contain at least two electrical conductors separated

by a dielectric (insulator). The capacitor is a reasonably general model for electric

fields within electric circuits. An ideal capacitor is wholly characterized by a

constant capacitance C, defined as the ratio of charge ±Q on each conductor to the

voltage V between them.

𝐶

Sometimes charge build-up affects the capacitor mechanically, causing its

capacitance to vary. In this case, capacitance is defined in terms of incremental

changes:

41

𝐶 𝑑

𝑑

6.1.4 Diode

The most common function of a diode is to allow an electric current to pass in one

direction (called the diode's forward direction), while blocking current in the

opposite direction (the reverse direction). Thus, the diode can be viewed as an

electronic version of a check valve. This unidirectional behavior is called

rectification, and is used to convert alternating current to direct current, including

extraction of modulation from radio signals in radio receivers—these diodes are

forms of rectifiers.

However, diodes can have more complicated behavior than this simple on–off

action. Semiconductor diodes begin conducting electricity only if a certain

threshold voltage or cut-in voltage is present in the forward direction (a state in

which the diode is said to be forward-biased). The voltage drop across a forward-

biased diode varies only a little with the current, and is a function of temperature;

this effect can be used as a temperature sensor or voltage reference.

Fig 3.8 diode symbol.

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6.1.5 Pulse Generator

6.b. Pulse Generator Symbol in simulink

The Pulse Generator block generates square wave pulses at regular

intervals. The block's waveform parameters, Amplitude, Pulse Width, Period, and

Phase Delay, determine the shape of the output waveform. The following diagram

shows how each parameter affects the waveform.

The Pulse Generator can emit scalar, vector, or matrix signals of any real

data type. To cause the block to emit a scalar signal, use scalars to specify the

waveform parameters. To cause the block to emit a vector or matrix signal, use

vectors or matrices, respectively, to specify the waveform parameters. Each

element of the waveform parameters affects the corresponding element of the

output signal. For example, the first element of a vector amplitude parameter

determines the amplitude of the first element of a vector output pulse. All the

waveform parameters must have the same dimensions after scalar expansion. The

data type of the output is the same as the data type of the Amplitude parameter.

Depending on the pulse's waveform characteristics, the intervals between

changes in the block's output can vary. For this reason, a time-based Pulse

Generator block has a variable sample time.

43

6.1.6 Resistor

A resistor is a passive two-terminal electrical component that implements

electrical resistance as a circuit element. The current through a resistor is in direct

proportion to the voltage across the resistor's terminals. This relationship is

represented by Ohm's law:

𝑅 𝑜 𝑡

Where I is the current through the conductor in units of amperes, V is the potential

difference measured across the conductor in units of volts, and R is the resistance

of the conductor in units of ohms.

Resistors are common elements of electrical networks and electronic circuits and

are ubiquitous in electronic equipment. Practical resistors can be made of various

compounds and films, as well as resistance wire (wire made of a high-resistivity

alloy, such as nickel-chrome). Resistors are also implemented within integrated

circuits, particularly analog devices, and can also be integrated

into hybrid and printed circuits.

6.c. various types of resistors.

44

6.1.7 Repeating Sequence:

6.d. Repeating Sequence symbol in Simulink

It generates arbitrarily shaped periodic signal.

The Repeating Sequence block outputs a periodic scalar signal having a waveform

that you specify. You can specify any waveform, using the block dialog's Time

values and Output values parameters. The Times value parameter specifies a

vector of sample times. The Output values parameter specifies a vector of signal

amplitudes at the corresponding sample times. Together, the two parameters

specify a sampling of the output waveform at points measured from the beginning

of the interval over which the waveform repeats (i.e., the signal's period). For

example, by default, the Time values and Output values parameters are both set to

[0 2]. This default setting specifies a sawtooth waveform that repeats every 2

seconds from the start of the simulation and has a maximum amplitude of 2. The

Repeating Sequence block uses linear interpolation to compute the value of the

waveform between the specified sample points.

6.1.8 Scope

6.e. Scope Symbol in Simulink.

The Scope block displays its input with respect to simulation time.

45

The Scope block can have multiple axes (one per port) and all axes have a

common time range with independent y-axes. The Scope block allows you to

adjust the amount of time and the range of input values displayed. You can move

and resize the Scope window and you can modify the Scope's parameter values

during the simulation.

If the signal is continuous, the Scope produces a point-to-point plot. If the

signal is discrete, the Scope produces a stair-step plot.

6.1.9 Power GUI

The Powergui block allows you to choose one of the following methods to solve

your circuit:

Continuous method, which uses a variable step Simulink solver

Ideal Switching continuous method

Discretization of the electrical system for a solution at fixed time steps

Phasor solution method

The Powergui block is necessary for simulation of any Simulink model containing

SimPowerSystems blocks. It is used to store the equivalent Simulink circuit that

represents the state-space equations of the model.

Place the Powergui block at the top level of diagram for optimal performance.

However, you can place it anywhere inside subsystems for your convenience; its

functionality will not be affected.

You can have a maximum of one Powergui block per model

You must name the block powergui

46

REFERENCES

1) Design and Modeling of Standalone Solar PhotovoltaicCharging System

By-Mathur B.L, Professor, Department of EEE, SSN College of

Engineering

2) Modelling of DC-DC converters

Ovidiu Aurel Pop and Serban Lungu

Technical University of Cluj-Napoca

Romania

3) www.mathworks.in

4) Irving M. Gottlieb, Power Supplies, Switching Regulators, Inverters, &

Converters, New York: McGraw-Hill, 1993, pp. 132-141.

5) Paper on PHOTOVOLTAIC CHARGE CONTROLLER

By: NOOR JUWAINA AYUNI BT. MOHD

6) Comparison of Photovoltaic array maximum power point tracking

technique - Patrick L Chapman, Trishan Esram

7) Texas Instruments papers

8) Power Electronics by Muhammad H. Rashid

9) Power Electronics by P. S. Bhimra

10) Development of a dc-dc buck boost converter using fuzzy logic control by fathi shaban jabber

11) F. Liu, S. Duan, F. Liu, B. Liu, and Y. Kang, ―A variable step size INC

MPPT method for PV systems,‖ IEEE Trans.Ind.Electron., vol. 55, no.

7,pp. 2622–2628, Jul. 2008.