Hybrid Power System

Implementation of a Hybrid Power System Prototype using Solar and Wind Energy

A Thesis Submitted

By

Islam, Md. Mahmudul 08-10472-1

Chowdhury, Md. Kawsar 08-09950-1

Rahman, Mahabubur Md. 07-09728-3

Ali, Shaiyan Moon A-Moon Ibne 08-10453-1

Under the supervision of

Chowdhury Akram Hossain

Lecturer

Faculty of Engineering

American International University- Bangladesh

Department of Electrical and Electronic Engineering Faculty of Engineering


Summer Semester 2010-2011

October 2011

i

Implementation of a Hybrid Power System Prototype using Solar and Wind Energy

A Thesis submitted to the Electrical and Electronic Engineering Department of the Engineering

Faculty, American International University - Bangladesh (AIUB) in partial fulfillment of the

requirements for the degree of Bachelor of Science in Electrical and Electronic Engineering.

1. Islam, Md. Mahmudul 08-10472-1

2. Chowdhury, Md. Kawsar 08-09950-1

3. Rahman, Mahabubur Md. 07-09728-3

4. Ali, Shaiyan Moon A-Moon Ibne 08-10453-1

Department of Electrical and Electronic Engineering Faculty of Engineering


Summer Semester 2010-2011

October 2011

ii

Declaration

This is to certify that this project and thesis is our original work. No part of this work has been

submitted elsewhere partially or fully for the award of any other degree or diploma. Any material

reproduced in this thesis has been properly acknowledged.

___________________________ 1. Islam, Md. Mahmudul

ID: 08-10472-1 Dept: EEE

___________________________ 2. Chowdhury, Md. Kawsar

ID: 08-09950-1 Dept: EEE

___________________________

3. Rahman, Mahabubur Md. ID: 07-09728-3

Dept: EEE

___________________________

4. Ali, Shaiyan Moon A-Moon Ibne ID: 08-10453-1

Dept: EEE

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Approval

The Project titled Implementation of a Hybrid Power System Prototype using Solar and Wind Energy has been submitted to the following respected members of the Board of Examiners of the Faculty of Engineering in partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical and Electronic Engineering on October 2011 by the following students and has been accepted as satisfactory.

i. Islam, Md. Mahmudul 08-10472-1

ii. Chowdhury, Md. Kawsar 08-09950-1

iii. Rahman, Mahabubur Md. 07-09728-3

iv. Ali, Shaiyan Moon A-Moon Ibne 08-10453-1

___________________________ __________________________ Chowdhury Akram Hossain Mohammad Nasir Uddin Supervisor External Supervisor Lecturer, Faculty of Engineering Assistant Professor, Faculty of Engineering American International University- American International University- Bangladesh (AIUB) Bangladesh (AIUB) ____________________________ ___________________________ Prof. Dr. ABM Siddique Hossain Dr. Carmen Z. Lamagna Dean, Faculty of Engineering Vice Chancellor American International University- American International University- Bangladesh (AIUB) Bangladesh (AIUB)

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Acknowledgements

We are heartily thankful to our supervisor, Chowdhury Akram Hossain, Lecturer, Faculty of

Engineering, whose encouragement, supervision and support from the preliminary to the

concluding level gave us the courage to finish our work successfully. We would also like to

express our gratitude towards our External Supervisor Mohammad Nasir Uddin, Assistant

Professor, Faculty of Engineering for his presence during our presentation and for the various

advices that he gave us for future development of the project. We also thank Prof. Dr. ABM

Siddique Hossain, Dean, Faculty of Engineering, and our respected Vice Chancellor, Dr. Carmen

Z. Lamagna, for giving us the opportunity to carry out a thesis of our choice. In the reference

section of this book, we have mentioned the names and authors of the papers and information

sources without which this project would not have been possible, and our gratitude reaches out to

all those authors.

The Faculty of Engineering of American International University- Bangladesh has provided us

with the knowledge and assistance that constructed the foundation required in us to initiate and

follow through a project such as this, and for that we are most grateful to all the teachers,

officers, and staff of the EEE Department.

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Abstract

The demand of power continues to rise day by day. Renewable energies available in nature can

definitely contribute as a solution towards this problem. In this project it has been shown that it is

possible to combine more than one or more source and generate power. The project uses energy

from light and wind to generate electricity. In coastal areas, especially those countries where it is

difficult to meet the increasing demand of electricity, the wind speed is sufficient most of the

time for the generation of electricity. In addition, the availability of sunlight definitely is another

option. In this project, the best source is chosen among the two whenever both of them are

available. The prototype was successfully able to charge a 4.5V battery and run a load along with

the charging process at the same time. A mobile phone was also connected for testing purpose,

and was successfully charged. This particular prototype can be thought of as a portable system,

and can be used for charging devices or run devices that require similar voltage during traveling.

Contents

Chapter 1 Introduction 1

1.1 History of Renwable Energy 1

Chapter 2 Renewable Energy 3

2.1 Introduction 4

2.2 Importance of renewable energy

2.3 Sources of renewable energy 5

Chapter 3 Solar Power 7

3.1 Solar energy 7

3.2 Solar Power 8

3.3 Photovoltaic Effect 8

3.4 Solar cell 8

3.5 Equivalent circuit of a solar cell 10

3.6 Material used in solar cells 10

3.7 Solar cell efficiency 11

3.8 The suns intensity 12

3.9 Temperature 13

3.10 Series resistance 14

Chapter 4 Wind Power 16

4.1 History 16

4.2 Nature of Wind 16

4.3 Windmill Basics 17

4.4 Components of a Wind Turbine Generator 18

4.5 Connection of Wind Energy Plants to the Grid 19

4.6 Wind Power generating system 19

4.7 Advantages of Wind Power 20

4.8 Disadvantages of Wind Power 21

Chapter 5 Transistors 22

5.1 Definition 22

5.2 Transistors used in the Project 23

5.3 Images and Pin Configuration 23

Chapter 6 Operational Amplifier 25

6.1 Definition 25

6.2 Circuit notation 25

6.3 Operation 26

6.4 Op-Amp Characteristics 27

6.5 Internal Circuitry of the 741 type Op-Amp 29

6.6 Application 30

Chapter 7 Boost Converter 31

7.1 Introduction 31

7.2 Application 31

7.3 Circuit Analysis 32

7.4 Continuous Mode 33

7.5 Discontinuous Mode 36

Chapter 8 Microcontroller Atmega-16 38

8.1 Features 38

8.2 Pin Configuration and Pin description 38

8.3 NEXTSAPIENS 40

8.4 Softwares used for Coding 41

8.5 Programming 43

Chapter 9 Hybrid Operation 45

9.1 Intoruction 45

9.2 Circuit Diagram and Operation 46

9.3 Four Main Operations 51

9.4 Charging of battery and feeding current to load using solar energy 52

9.5 Charging of battery and feeding current to load using solar energy 52

9.6 Current fed to the load directly from renewable source 54

9.7 Current fed to the load directly from battery 55

9.8 Experimental Analysis 55

Chapter 10 Discussion and Conclusion 57

10.1 Discussions 57

10.2 Suggestions for future work 58

10.3 Conclusion 59

Reference 60

DATASHEET 61

1

Chapter 1

Introduction

1.1 History of Renewable Energy

Modern renewable energy technology dates from the second half of the 20th century

however the use of renewable resources for energy dates from when early humans learned to

control use of fire.

Besides burning wood and other flammable materials, our ancestors in ancient times took

advantage of the majority of the natural resources we know today: water, wind, sun and even

geothermal heat.

The power of the sun has been known and used already in ancient times which we can see at

the oculus at the top of famous Pantheon in Rome, Italy, which was built in the first half of

the 2nd century AD. Until the early 20th century when electrical lighting became the

predominant interior lighting, sunlight was the only source of light besides candles, torches,

oil lamps and after the industrial revolution in the second half of the 18th century - kerosene

lamps.

Sunlight has been used for making fire which is clearly indicated the writings of Lucian of

Samosa in the 2nd century AD who wrote that during the Siege of Syracuse (3rd century BC)

Archimedes repelled the Roman attack with a burning-glass. In addition to solar power,

sources of energy used were wind and water.

Since ancient times wind was used for propelling ships and to turn windmills whilst rivers

have turned water wheels for millennia, the Romans even used geothermal water for heating.

Until the middle of the 18th century and the discovery of fossil fuels, renewable sources were

the only sources of energy available to man.

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Excessive use of fossil fuels has caused global climate change which has became obvious in

the last few decades and has forced people and governments throughout the world to

seriously reconsider the replacement of fossil fuels with renewable energy sources.

3

Chapter 2

Renewable Energy

2.1 Introduction

Renewable energy uses energy sources that are continuously available in nature such as- the

sun, wind, water, the Earths heat and plants. Renewable Energy technologies turn these fuels

into usable forms of energy. Till now fossil fuels are used as the main source of energy. But

there is a limited supply of these fuels, and they are being used much more rapidly than they

are created. So the amount of coal, oil and natural gas is decreasing day by day but demand

of energy is increasing. Also usage of fossil fuels has negative impact on nature. Nuclear

power came as an alternative, but it is very expensive and it has safety concerns and waste

disposal problem. Under all these circumstances renewable energy is the best option for

producing energy safely.

Figure 2.1: global energy sources

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2.2 Importance of renewable energy

The main source of energy is oil. Different researches brought out that in 150 years, half of

the global oil reserve that took hundreds of millions of years to produce has been used by

mankind. Recent data indicate that global oil production has been constant since 2005 and

possibly is the early indicator that we are at the peak.

Figure 2.2: The growing gap between oil production and new oil fields finds

Due to excessive use, amount of other fuels like natural gas, coal is also decreasing rapidly.

More than 90% of greenhouse gas emissions come from the combustion of fossil fuels.

Combustion of fossil fuels also produces other air pollutants, such as nitrogen oxides, sulfur

dioxide, volatile organic compounds and heavy metals. Combustion of fossil fuels generates

sulfuric, carbonic, and nitric acids, which fall to Earth as acid rain, impacting both natural

areas and environment. Monuments and sculptures made from marble and limestone are

5

particularly vulnerable, as the acids dissolve calcium carbonate. Fossil fuels also contain

radioactive materials like uranium and thorium.

The principal risks associated with nuclear power arise from health effects of radiation. This

radiation consists of subatomic particles traveling at or near the velocity of light 186,000

miles per second. They can penetrate deep inside the human body where they can damage

biological cells and thereby initiate a cancer. The radioactive waste products from the nuclear

industry must be isolated from contact with people for very long time periods. This high level

waste will be converted to a rock-like form and emplaced in the natural habitat of rocks, deep

underground. The average lifetime of a rock in that environment is one billion years. If the

waste behaves like other rock, it is easily shown that the waste generated by one nuclear

power plant will eventually, over millions of years cause one death from 50 years of

operation. Moreover the recent tsunami in Japan once again proved that nuclear power is not

safe at all.

On the other hand, there is infinite supply of renewable energy sources, they are not harmful

to the environment and also provides safety.

So, due to shortage of fossil fuels, pollution and safety reasons it is essential to find out an

alternative energy source for the future generation. Thats why the concept of renewable

energy is very important. Scientists and engineers all over the world are researching on

renewable energy.

2.3 Sources of renewable energy

Various sources of renewable energy are:

Solar energy.

Wind power.

Hydropower.

6

Biomass.

Bio-fuel.

Geothermal energy.

In recent time, engineers and scientists are looking for a possibility to genrate energy from

sound.

7

Chapter 3

Solar Power

3.1 Solar energy

Solar Energy is the energy from the Sun .The Earth receives an incredible supply of solar

energy. The sun is a fusion reactor that has been burning over 4 billion years. It provides

enough energy in one minute to supply the world's energy needs for one year. In one day, it

provides more energy than our current population would consume in 27 years. In fact, the

amount of solar radiation striking the earth over a three-day period is equivalent to the energy

stored in all fossil energy sources.

Figure 3.1: Solar Radiation

8

Solar energy is a free resource. The ability to use solar power for heating water was the first

discovery to use solar energy. Producing electricity from solar energy was later discovered.

3.2 Solar Power

The concept of solar power is based on photovoltaic effect, so before discussing about solar

power it is needed to learn about photovoltaic effect.

3.3 Photovoltaic Effect

Photovoltaic effect is the creation of voltage in a material with exposure of light. It is quite

similar to photoelectric effect, but the operation is different. Instead of ejecting electrons, in

photovoltaic effect the generated electrons are transferred between different bands.

When a photovoltaic (PV) cell is exposed to the suns thermal radiation, it absorbs the

thermal energy and converts it directly into DC electrical energy. The size of the PV cell and

the DC voltage and energy it can deliver are small. A number of these cells are mounted on a

plate and connected in series and parallel. These plates together form a solar array. These

arrays require sizeable exposed area and reasonably clear skies to deliver useable quantities

of electrical energy. Exploiting solar energy and converting it into an electrical form has been

under intense development for a long time. The main advantage of PV cell is that it

consumes no fuel. No fuel consumption results no pollution.

3.4 Solar cell

Semiconductors are used to make solar cell. In semiconductors, the filled band (valence

band) and the band in which electrons are free to move (conduction band) are separated by a

potential difference of about 1 volt. Hence, light coming in can push an electron from the

valence band into the conduction band if it has energy of about 1 electron volt (1 eV). The

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electron in the conduction band is free to move. If it is kept from recombining, it can give up

its energy in an external circuit before coming back to the material.

Figure 3.2: Energy Diagram

When light shines, electrons are liberated in the p-type region and holes produced in the n-

type region; this lowers the potential energy barrier at the junction. A current flows and

establishes an external potential difference.

Figure 3.3: Inside a Photovoltaic System

Solar cells act in a way similar to the diode, so that current can flow in only one direction

when the cell is exposed to light.

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3.5 Equivalent circuit of a solar cell

Figure 3.4: Simple equivalent circuit for a solar cell

The solar cell can be seen as a current generator which generates the current (density) Jsc.

The dark current flows in the opposite direction and is caused by a potential between the +

and - terminals. In addition there might be two resistances, one in series (Rs) and one in

parallel (Rp). The series resistance is caused by the fact that a solar cell is not a perfect

conductor. The parallel resistance is caused by leakage of current from one terminal to the

other due to poor insulation. In an ideal solar cell, Rs = 0 and Rp = .

3.6 Material used in solar cells

The most popular choice for solar cells is silicon (Si), with a band gap of 1.1 eV,production

cell efficiencies of about 12 % and a maximum efficiency of about15%, and gallium

arsenide, with a band gap of 1.4 eV and a maximum efficiency of about 22%. The maximum

theoretical efficiency for a single cell is 33%. For multiple cells, the theoretical maximum is

68%. Both of these materials must be grown as single crystals under very precisely

controlled conditions to minimize imperfections, which can cause recombination.

The material gallium arsenide (GaAs) is also very popular for solar cells. Gallium and

arsenic are exactly one atomic higher and lower than silicon, so the system has many

similarities to a silicon-based semiconductor. It is less friable than silicon, more resistant to

11

radiation damage, and so is the material of choice in space-based solar cells. Doping this

material with atoms from nearby columns in the periodic table changes the properties a bit.

Additionally, only very thin films of gallium arsenide need be used since it is so effective at

absorbing light. About half the energy in sunlight is unusable by most PV cells because this

energy is below the band gap, and so cant free an electron from the valence to the

conduction band, or because it carries excess energy, which must be transferred to the cell

as thermal energy, heating up the cell.

Figure 3.5: different properties of silicon, gallium arsenide, and aluminum gallium arsenide

3.7 Solar cell efficiency

The efficiency of a solar cell depends on many factors. It is therefore possible that a single

solar cells performance varies widely depending on its location. This presents the industry

with a problem. The power of a solar cell is expressed in wattpeak (Wp), which represents its

efficiency under laboratory conditions. These conditions are set at a temperature of 25C, a

light travel distance of 1.5 air mass and a light intensity of 1 kw/m2. This theoretical limit is

almost never reached.

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3.8 The suns intensity The first factor is probably the most obvious. The brighter the sunlight, the more there is for

the solar cell to convert. It is for this reason that a solar cell performs best during spring and

summer; in fall and winter the sunlight is less intense and thus less able to kick loose the

electrons from their parent atoms. This mainly reduces the flow of current; the voltage is

usually not that much affected. It is also due to this factor, that a solar cell will be able to

deliver more energy in the sunnier areas. The map below is the so-called insolation map for

the United States. It displays the average amount of kilowatt-hours received per day. Since a

solar cells performance is measured at an intensity of 1 kw/m2, the insolation can also be

read as the average amount of daily hours of sunshine. The definition of one hour of

sunshine is chosen to match the laboratory conditions of the solar cell specifications (1

kW/m2).

Figure 3.6: insolation map

13

Figure 3.7: Daily Insolation Curve

3.9 Temperature

Contrary to popular belief, the efficiency of a solar cell decreases with increasing

temperature. The reason for this is that a higher temperature increases the conductivity of the

semiconductor. This balances out the charge within the material, reducing the magnitude of

the electric field at the junction. This in turn inhibits charge separation, which lowers the

voltage across the cell. It should be noted that a higher temperature increases the mobility of

electrons, which causes the flow of current to increase slightly. This increase is however

minor and insignificant compared to the decrease in voltage.

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Figure 3.8: effect of temperature on solar cell

This figure displays the response of a solar cell to varying temperature. The current increases

slightly, whilst the voltage decreases rapidly. The result is a lower overall power yield

(P=V*I).

The listed power of a solar cell is the power measured under ideal laboratory conditions,

which prescribe a temperature of 25 C (77 F). However, on a typical hot summer day, it is

not uncommon for a solar cell to reach a temperature of 70 C (158 F). A general rule of

thumb is that the efficiency of a solar cell decreases with 0.5% for every 1 C (1.8 F) above

25 C (77 F). This means that on a hot summer day, the efficiency of a solar cell could drop

as much as 25%. It is therefore extremely important to keep solar panels well ventilated.

3.10 Series resistance

When tying solar cells together, it is important to keep series resistance of the circuit to a

minimum. Resistance directly influences both voltage and current, and an increasing

resistance will cause the voltage-current curve of the solar cell to move away from the

maximum power point (MPP). At this point, a solar cell produces maximum output (through

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the equation P=V*I) and it is thus advantageous to maintain this point. Since the material in a

solar cell acts as a resistor to current flow, it is often advisable to limit the amount of serially

connected solar cells. By wiring individual serial batches of solar cells in parallel can be

overcome

Figure 3.9: Effect of series resistance in solar cell

This figure displays the effect of series resistance on a solar cells output voltage and current.

By increasing series resistance, the solar cell moves away from the maximum power point.

16

Chapter 4

Wind Power

4.1 History

Wind power has been utilized by mankind since historical times. Windmills have been

getting increasing attention on account of wind energy being available free of cost and also

on account of being the most nonpolluting source of electricity. On the electricity front, it

started with a wind turbine driving an electricity generator, mainly an induction motor, which

is universally available. The output ratings were minuscule, a few hundred watts. Today, it is

entering into the club of megawatt-scale electricity producers. Kriegers Flak, an island

located in the Baltic Sea between Sweden, Denmark, and Germany, is expected to fully

commission its wind farm rated at 630 MW by 2010.

The latest rates of growth are striking. In Europe, wind farm installations grew at a rate of

38% during 2007, compared to 19% during 2006. By 2007, total installed wind power

capacity there stood at 67 GW. Germany, Denmark, and Portugal were prominent. In the

United States, total wind farm capacity stood at 11 GW in 2007. It is growing fast in China,

India, and many other countries.

Yet, total contribution by wind energy to production of world electricity energy at the

beginning of 2006 has been very minuscule, 0.7% of the total of 17,500 TW -hr. It has its

drawbacks by its very nature.

4.2 Nature of Wind

Wind may blow steadily during certain periods, varying by day, season, location, and so on.

Let us say the velocities fall within some zones. The wind may die down, falling to almost

nil. Then it may rise from a very low speed. There may be a wind lull, when the wind dies

out and then raises in short bursts. A wind gust is the opposite phenomenon to a wind lull. A

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very strong wind is a storm. This nature of wind makes it an unreliable source of power due

to its variability and uncertainty.

4.3 Windmill Basics

The idea behind generating electricity from wind is quite simple. Wind is the manifestation

of the kinetic energy of air molecules in the atmosphere. In order to use this kinetic energy

for other purposes, all that one has to do is to have the wind hit a surface that is allowed to

move. This will cause the kinetic energy of the wind to be converted to the kinetic energy of

the moving object. Anyone who has ever been outside on a very windy days understands

these concepts. The hard part about generating electricity from wind is doing it cheaply. To

do this, a more fundamental knowledge about wind energy is needed

Let us imagine air that is moving through an area A with a velocity v as shown in following

figure. It is known that the kinetic energy of an individual air molecule is given by the

formula 1/2 mv2.

Now consider a large system of air molecules, which means looking at a volume of particles.

In a time t, the mass of the air that will flow through the area A is given by m = A v t,

where is the density of the air. Put these two formulae together, the kinetic energy of the air

that passes through an area A in a time t is given by the formula 1/2 A v3 t. Since the

energy per unit time is equal to the power, the power in the wind moving through the area A

is given by

P = K.E./t = 1/2 A v3

Figure 4.1: Diagram of wind tube

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In 1919, a German physicist by the name of Albert Betz showed that the maximum amount of

power that one can get from the wind is only 59% of that given by the formula above. In

actuality, less than this maximum amount is getable. Therefore, the formula for the power

from a wind turbine is written as,

P = 1/2 C A v3

Where, the factor C depends on the actual design of the windmill. The factors that affect the

constant C are many and complicated.

4.4 Components of A Wind Turbine Generator:

The following figure shows the components of a wind turbine generator. These are mainly:

1. The rotor blades, whose pitch is adjustable as per wind velocity so as to catch maximum wind energy, 2. The gear box which adjusts the rpm of the rotor of the generator as closely as possible to the grid synchronous frequency. 3. The generator, which converts mechanical input into an electrical output.

Figure 4.2: a wind turbine generator

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4.5 Connection of Wind Energy Plants to the Grid

In the early days of wind electricity generation, the plant sizes were small. With an induction

generator, there was no problem of synchronizing with grid frequency. External capacitors

took care of voltages; when there was a disturbance in the grid leading to low voltages at the

point of connection, the wind plants were disconnected and stayed disconnected until the grid

disturbance was cleared. Today, wind plant sizes have increased. Should a wind plant get

disconnected due to a grid disturbance, it could aggravate the situation. A grid code for

interconnection has evolved. The mean features of the grid codes are:

1. Accurate power control at a PF of 0.95 has to be maintained at the point of connection.

2. Accurate plant models must be submitted.

3. SCADA data must be supplied as agreed with the system operator.

4.6 Wind Power generating system

A small DC motor has been used for this purpose. The fact that a motor can be used as a

generator has been applied here. The motor used in this project looks somewhat like the one

shown below in the picture:

Figure 4.3: A small DC motor

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This motor is a DC motor consisting of a brush. The brushed DC electric motor generates

torque directly from DC power supplied to the motor by using internal commutation,

stationary magnets (permanent or electromagnets), and rotating electrical magnets.

Like all electric motors or generators, torque is produced by the principle of Lorentz Force,

which states that any current-carrying conductor placed within an external magnetic field

experiences a torque or force known as Lorentz force. Advantages of a brushed DC motor

include low initial cost, high reliability, and simple control of motor speed. Disadvantages

are high maintenance and low life-span for high intensity uses. Maintenance involves

regularly replacing the brushes and springs which carry the electric current, as well as

cleaning or replacing the commutator. These components are necessary for transferring

electrical power from outside the motor to the spinning wire windings of the rotor inside the

motor. For the required operation of this project, a small fan consisting of three blades is

connected to the shaft of the motor. By applying sufficient wind from a suitable source, s

small table fan for example, the blades can be made to rotate which creates a potential

difference across the ends of the motor.

4.7 Advantages of Wind Power

1. The wind is free and with modern technology it can be captured efficiently.

2. Once the wind turbine is built it doesnt cause green house effect.

3. Although wind turbines can be very tall each takes up only a small plot of land. This

means that the land below can still be used. This is especially the case in agricultural areas as

farming can still continue.

4. Remote areas that are not connected to the electricity power grid can use wind turbines to

produce their own supply.

5. Wind turbines have a role to play in both the developed and third world.

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6. Wind turbines are available in a range of sizes which means a vast range of people and

businesses can use them. Single households to small towns and villages can make good use

of range of wind turbines available today.

4.8 Disadvantages of Wind Power

1. The electricity produced will not be constant since wind speed varies everywhere through out the world. At times there wont be any production of electricity. 2. Wind turbines are noisy. Each one can generate the same level of noise as a family car traveling at 70 mph.

3. Another of the disadvantages is that they can be damaged in thunderstorms, partially because of their tall, thin shape. The website of the National Lightning Safety Institute indicates that most damage to wind turbines is caused by lightening. This is more of a problem in warmer parts of the world, where they are frequent. 4. Pollution is caused to some extent by the turbines.

5. Large wind farms are needed to provide entire communities with enough electricity. For example, the largest single turbine available today can only provide enough electricity for 475 homes, when running at full capacity.

22

Chapter 5

Transistors

5.1 Definition

The transistor, invented by three scientists at the Bell Laboratories in 1947, rapidly replaced

the vacuum tube as an electronic signal regulator. A transistor regulates current or voltage

flow and acts as a switch or gate for electronic signals. A transistor consists of three layers of

a semiconductor material, each capable of carrying a current. A semiconductor is a material

such as germanium and silicon that conducts

Electricity in a "semi-enthusiastic" way, it's somewhere between a real conductor such as

copper and an insulator (like the plastic wrapped around wires).

The semiconductor material is given special properties by a chemical process called doping.

The doping results in a material that either adds extra electrons to the material (which is then

called N-type for the extra negative charge carriers) or creates "holes" in the material's crystal

structure (which is then called P-type because it results in more positive charge carriers). The

transistor's three-layer structure contains an N-type semiconductor layer sandwiched between

P-type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN

configuration).

A small change in the current or voltage at the inner semiconductor layer (which acts as the

control electrode) produces a large, rapid change in the current passing through the entire

component. The component can thus act as a switch, opening and closing an electronic gate

many times per second. Today's computers use circuitry made with complementary metal

oxide semiconductor (CMOS) technology. CMOS uses two complementary transistors per

gate (one with N-type material; the other with P-type material). When one transistor is

maintaining a logic state, it requires almost no power.

23

Transistors are the basic elements in integrated circuits (ICs), which consist of very large

numbers of transistors interconnected with circuitry and baked into a single silicon microchip

or "chip."

5.2 Transistors used in Project

The two type of transistors used in our project are MOSFET and BJT. The full form

MOSFET is metal-oxide semiconductor field-effect transistor, whereas, the full form of BJT

is bipolar-junction-transistor.

The MOSFET used is the Power MOSFET IRF540N.

The BJT used is 2N3055 NPN transistor.

Both these transistors have been used for switching purpose. The BJT has been used in a

boost converter circuit because it is a current controlled and also provides faster switching

time. Using a MOSFET in that case wouldnt provide the desired result.

5.3 Image and Pin Configuration

Figure 5.1: Image of 2N3055

Pin Configuration is quite simple. There is no pin for collector; the case itself acts as the

collector pin. The base is where the pulse has to be applied to ensure the flow of current from

collector to emitter.

24

Figure 5.2: Image of IRF540N

The pin marked 1, 2 and 3 are the gate, drain and source pin respectively. Here, pulse has to

be applied to the gate terminal to ensure that switching is possible.

25

Chapter 6

Operational Amplifier

6.1 Introduction

Op-Amp is a kind of electrical device which is used as a DC coupled high voltage electric

amplifier which have different input and one output. Op-Amp is basically used for creating a

high voltage in the output whatever the input is given. An op-amp can create hundred or

thousand time larger output than the voltage difference between the input terminals.

Operational amplifiers are important electrical components for a wide range of electronic

circuits. Op-Amp was used for the first time in the analog computer. They were used in

many linear, non-linear and frequency-dependent circuits in analog computer. Its popularity

and importance increase for the characteristics of the final op-amp circuits with negative

feedback (such as their gain) are set by external components with a slightly dependence on

temperature changes.

Op-Amp is a differential amplifier. The difference which makes op-amp more efficient from

the other differential amplifier is those amplifier mostly have two output where op-amp is

only one output. The instrumentation amplifier (basically built from three op-amps), the

isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-

mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier

(usually built from one or more op-amps and have a resistive feedback network).

6.2 Circuit notation

Figure 6.1: Circuit diagram symbol for an op-amp

26

The circuit symbol for an op-amp is shown to the right, where:

Vs+: positive power supply

Vs-: negative power supply

V+: non-inverting input

V-: inverting input

Vout: output.

To provide additional power for amplification of the signal. Often these pins are left out of

the diagram for clarity, and the power configuration is described or assumed from the circuit.

6.3 Operation

Figure 6.2: An op-amp without negative feedback (a comparator)

The amplifiers differential input have +V input and a V input and ideally the op-amp

amplifies the difference in voltage between this two, these are called the differential input

voltage. The output voltage is calculated by the equation given below:

Vout= (V+ - V-).AOL

Where,

AOL = open-loop gain of the amplifier.

V+ = voltage at the non-inverting terminal

V- = voltage at the inverting terminal

27

The amount of AOL is naturally very large; therefore even a slightly small difference between

V+ and V- drives the amplifier output just about to the supply voltage. This is called

saturation of the amplifier. And the saturation cant be controlled by the manufacturing

process. And this is a very vital draw back for the op-amp because for this we cant use an

operational amplifier just as a differential amplifier.

6.4 Op-Amp characteristic

Ideal Op-Amps: An ideal op-amp is usually considered to have the following properties:

1. Infinite voltage range available at the output (vout) (in practice the voltages available from the output are limited by the supply voltages Vs- and Vs+). The power supply sources are called rails.

2. Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as open loop gain AOL goes to infinity).

3. Infinite input impedance (so, in the diagram, Rin=, and zero current flows from V+ to V-).

4. Zero output impedance (i.e., Rout = 0, so that output voltage does not vary with output current).

5. Zero input current (i.e., there is assumed to be no leakage or bias current into the device).

6. Zero input offset voltage (i.e., when the input terminals are shorted so that V+= V-, the output is a virtual ground or vout = 0).

7. Infinite bandwidth (i.e., the frequency magnitude response is considered to be flat everywhere with zero phase shift).

8. Infinite slew rate (i.e., the rate of change of the output voltage is unbounded) and power bandwidth (full output voltage and current available at all frequencies).

9. Zero noise.

28

These ideals can be summarized by the two rules:

1. The inputs draw no current

2. The output attempts to do whatever is necessary to make the voltage difference between

the inputs zero.

In practice, none of these ideals can be perfectly realized, and different shortcomings and

compromises have to be accepted. Depending on the parameters of interest, a real op-amp

may be designed to take account of some of the non-infinite or non-zero parameters using the

same resistors and capacitors in the op-amp design. The designer can then include the effects

of these unwanted, but real, effects into the overall performance of the final circuit. Some

parameters may turn out to have a effect which is very negligible on the final design while

others represent actual limitations of the final performance, that must be evaluated.

Figure 6.3: An equivalent circuit of an operational amplifier that models some resistive non-

ideal parameters.

29

6.5 Internal circuitry of 741 type op-amp:

Figure 6.4: A component level diagram of the common 741 op-amp. Dotted lines outline:

current mirrors (red); differential amplifier (blue); class A gain stage (magenta); voltage

level shifter (green); output stage (cyan).

Though designs differ between products and manufacturers, all op-amps have basically the

same internal structure, which consists of three stages:

1. Differential amplifier provides low noise amplification, high input impedance,

usually a differential output.

2. Voltage amplifier provides high voltage gain, a single-pole frequency roll-off,

usually single-ended output.

3. Output amplifier provides high current driving capability, low output impedance,

current limiting and short circuit protection circuitry.

IC op-amps as implemented in practice are quite complex integrated circuits. A typical

example is the ubiquitous 741 op-amp designed by Dave Fullagar in Fairchild Semiconductor

after the remarkable Widlar LM301. Thus the basic architecture of the 741 is identical to that

of the 301.

30

6.6 Application:

In this project, the operational amplifier amplifies any voltage from the two renewable

sources. Two resistors of 1K and 10K have been used, while the two inputs are connected to

the positive input terminal of the operational amplifier. Since the ratio between the two

resistors is 10 so we get an amplification which is 11 times that of the input. The operation is

chosen such that, if the voltage of either of the input is at least 1.5V then it goes to the input

of the amplifier. Depending on the efficiency, either of solar or wind is chosen when both are

available.

Figure 6.5: An op-amp with negative feedback (a non-inverting amplifier)

31

Chapter 7

Boost Converter

7.1 Introduction

A boost converter (step-up converter) is a power converter with an output DC voltage greater

than its input DC voltage. It is a class of switching mode power supply (SWPS) containing at

least two semiconductor switches (a diode and a transistor) and at least one energy storage

element. Filters made of capacitors (sometimes in combination with inductors) are normally

added to the output of the converter to reduce output voltage ripple.

A boost converter is a dc-dc converter with an output voltage greater than the source voltage.

A boost converter is sometimes called a step-up converter since it steps up the source

voltage. Since power (P = VI) must be conserved, the output current is lower than the source

current.

7.2 Applications

Battery powered systems often stack cells in series to achieve higher voltage. However,

sufficient stacking of cells is not possible in many high voltage applications due to lack of

space. Boost converters can increase the voltage and reduce the number of cells. Two

battery-powered applications that use boost converters are hybrid electric vehicles (HEV)

and lighting systems.

The NHW20 model Toyota Prius HEV uses a 500 V motor. Without a boost converter, the

Prius would need nearly 417 cells to power the motor. However, a Prius actually uses only

168 cells and boosts the battery voltage from 202 V to 500 V. Boost converters also power

devices at smaller scale applications, such as portable lighting systems. A white LED

typically requires 3.3 V to emit light, and a boost converter can step up the voltage from a

single 1.5 V alkaline cell to power the lamp. Boost converters can also produce higher

32

voltages to operate cold cathode fluorescent tubes (CCFL) in devices such as LCD backlights

and some flashlights.

A boost converter is used as the voltage increase mechanism in the circuit known as the

'Joule thief'. This circuit topology is used with low power battery applications, and is aimed

at the ability of a boost converter to 'steal' the remaining energy in a battery. This energy

would otherwise be wasted since the low voltage of a nearly depleted battery makes it

unusable for a normal load. This energy would otherwise remain untapped because many

applications do not allow enough current to flow through a load when voltage decreases. This

voltage decrease occurs as batteries become depleted, and is a characteristic of the ubiquitous

alkaline battery. Since (P = V2 / R) as well, and R tends to be stable, power available to the

load goes down significantly as voltage decreases.

7.3 Circuit Analysis

Operating Principle: The key principle that drives the boost converter is the tendency of an

inductor to resist changes in current. When being charged it acts as a load and absorbs energy

(somewhat like a resistor; it is to be noticed that base pulse of the transistor which has been

used as the switch should be less than millisecond to reduce the chance to damage the

inductor); when being discharged it acts as an energy source (somewhat like a battery). The

voltage it produces during the discharge phase is related to the rate of change of current, and

not to the original charging voltage, thus allowing different input and output voltages.

Figure 7.1: Boost converter schematic

33

Figure 7.2: The two configurations of a boost converter, depending on the state of the switch

S.

The basic principle of a Boost converter consists of 2 distinct states

In the On-state, the switch S is closed, resulting in an increase in the inductor current; In the Off-state, the switch is open and the only path offered to inductor current is

through the diode D, the capacitor C and the load R. This result in transferring the energy accumulated during the On-state into the capacitor.

The input current is the same as the inductor current as can be seen in figure 2. So it is not discontinuous as in the buck converter and the requirements on the input filter are relaxed compared to a buck converter.

7.4 Continuous mode

Figure 7.4: Waveforms of current and voltage in a boost converter operating in continuous

mode

34

When a boost converter operates in continuous mode, the current through the inductor (IL)

never falls to zero. Figure shows the typical waveforms of currents and voltages in a

converter operating in this mode. The output voltage can be calculated as follows, in the case

of an ideal converter (i.e. using components with an ideal behavior) operating in steady

conditions:

During the On-state, the switch S is closed, which makes the input voltage appear across the

inductor, which causes a change in current (IL) flowing through the inductor during a time

period (t) by the formula:

At the end of the On-state, the increase of IL is therefore:

D is the duty cycle. It represents the fraction of the commutation period T during which the

switch is on. Therefore D ranges between 0 (S is never on) and 1 (S is always on).

During the Off-state, the switch S is open, so the inductor current flows through the load. If

we consider zero voltage drop in the diode, and a capacitor large enough for its voltage to

remain constant, the evolution of IL is:

Therefore, the variation of IL during the Off-period is:

As we consider that the converter operates in steady-state conditions, the amount of energy

stored in each of its components has to be the same at the beginning and at the end of a

commutation cycle. In particular, the energy stored in the inductor is given by:

L

Vo-Vi

=

di dt L

=

It t

Vi L L

ILon

=

1 L

Vi dt

=

DT

0

DT Vi

L L

=

ILoff

(Vi- Vo) (1-D)T L

=

T

DT

(Vi- Vo) T L

E

=

0.5L IL2

35

=

ILon

+

ILoff

0

So, the inductor current has to be the same at the start and end of the commutation cycle.

This means the overall change in the current (the sum of the changes) is zero:

Substituting ILon and ILoff by their expressions yields:

This can be written as:

This in turns reveals the duty cycle to be:

From the above expression it can be seen that the output voltage is always higher than the

input voltage (as the duty cycle goes from 0 to 1), and that it increases with D, theoretically

to infinity as D approaches 1. This is why this converter is sometimes referred to as a step-up

converter.

ILon

+

ILoff

=

=

ViDT L

(Vi- Vo) (1-D)T L

0

=

Vo Vi

1 (1-D)

=

D

Vo Vi

1

-

36

7.5 Discontinuous mode

Figure 7.4: Waveforms of current and voltage in a boost converter operating in

discontinuous mode

In some cases, the amount of energy required by the load is small enough to be transferred in

a time smaller than the whole commutation period. In this case, the current through the

inductor falls to zero during part of the period. The only difference in the principle described

above is that the inductor is completely discharged at the end of the commutation cycle (see

waveforms in figure 4). Although slight, the difference has a strong effect on the output

voltage equation. It can be calculated as follows:

As the inductor current at the beginning of the cycle is zero, its maximum value ILMAX(at t =

DT) is

During the off-period, IL falls to zero after T:

Using the two previous equations, is:

ILmax

=

ViDT L

ILmax

+

(Vi- Vo) T L

=

0

=

ViD (Vi- Vo)

37

The load current Io is equal to the average diode current (ID). As can be seen on figure 4, the

diode current is equal to the inductor current during the off-state. Therefore the output

current can be written as:

Replacing Imax and by their respective expressions yields:

Therefore, the output voltage gain can be written as follows:

Compared to the expression of the output voltage for the continuous mode, this expression is

much more complicated. Furthermore, in discontinuous operation, the output voltage gain not

only depends on the duty cycle, but also on the inductor value, the input voltage, the

switching frequency, and the output current.

Io

=

ID

ILmax

2 L

=

Io

=

*

ViDT 2L

ViD (Vi- Vo)

=

Vi2 D2T 2L(Vi- Vo)

=

1

+

Vi2 D2T 2LIo

Vo Vi

38

Chapter 8

Microcontroller ATmega-16

8.1 Features

The following are some of the common features of the microcontroller used in this project.

1. Advanced RISC Architecture. 2. Up to 16 MIPS Throughput at 16 MHz. 3. 16K Bytes of In-System Self-Programmable Flash. 4. 512 Bytes EEPROM. 5. 1K Byte Internal SRAM. 6. 32 Programmable I/O Lines. 7. In-System Programming by On-chip Boot Program. 8. 8-channel, 10-bit ADC. 9. Two 8-bit Timer/Counters with Separate Prescalers and Com. 10. One 16-bit Timer/Counter with Separate Prescaler, Compare. 11. Four PWM Channels. 12. Programmable Serial USART. 13. Master/Slave SPI Serial Interface. 14. Byte-oriented Two-wire Serial Interface. 15. Programmable Watchdog Timer with Separate On-chip Oscill. 16. External and Internal Interrupt Sources.

8.2 Pin Configuration and Pin Descriptions

The pin descriptions are as follows:

VCC: Digital supply voltage. (+5V)

GND: Ground. (0 V) Note there are 2 ground Pins.

Port A (PA7 - PA0): Port A serves as the analog inputs to the A/D Converter. Port A also

serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. When pins PA0 to

39

PA7 are used as inputs and are externally pulled low, they will source current if the internal

pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes

active, even if the clock is not running.

Port B (PB7 PB0): Port B is an 8-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). Port B also serves the functions of various special features of the

Atmega16.

Port C (PC7 PC0): Port C is an 8-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). Port C also serves the functions of the JTAG interface and other

special features of the ATmega16. If the JTAG interface is enabled, the pull-up resistors on

pins PC5(TDI), PC3(TMS) and PC2(TCK) will be activated even if a reset occurs.

Port D (PD7 - PD0): Port D is an 8-bit bi-directional I/O port with internal pull-up resistors

(selected for each bit). Port D also serves the functions of various special features of the

Atmega16.

RESET: Reset Input. A low level on this pin for longer than the minimum pulse length will

generate a reset, even if the clock is not running.

XTAL1: External oscillator pin 1

XTAL2: External oscillator pin 2

AVCC: AVCC is the supply voltage pin for Port A and the A/D Converter. It should be

externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be

connected to VCC through a low-pass filter.

AREF: AREF is the analog reference pin for the A/D Converter.

40

Figure. Atmega16 Pin Configurations

8.3 NEXTSAPIENS

The burner used for the microcontroller used in this project is NEXTSAPIENS. The features

are as follows:

1. 40 Pin Atmel ATmega16/32 microcontroller with internal system clock up to 8 MHz and externally up to 16 MHz

2. 16/32 KB FlashRAM memory for programs.

3. 1/2 KB of SRAM .

4. 512/1024 Bytes of EEPROM. 5. One 6x1 Pin SPI Relimate Header.

6. Eight 3x1 Pin Relimate header inputs for 8 analog sensors.

PA0(ADC0) PA1(ADC1) PA2(ADC2) PA3(ADC3) PA4(ADC4) PA5(ADC5) PA6(ADC6) PA7(ADC7) AREF GND AVCC PC7(TOSC2) PC6(TOSC1) PC5(TD1) PC4(TD0) PC3(TMS) PC2(TCK) PC1(SDA) PC0(SCL) PD7(OC2)

(XCK/T0)PB0 (T1)PB1

(INT2/AIN0)PB2 (OC0/AIN1)PB3

(SS)PB4 (MOSI)PB5 (MISO)PB6

(SCK)PB7 RESET

VCC GND

XTAL2 XTAL1

(RXD)PD0 (TXD)PD1 (INT0)PD2 (INT1)PD3

(OC1B)PD4 (OC1A)PD5

(ICP1)PD6

40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

41

7. One 16 Pin header to connect 16*2 alphanumeric LCD.

8. Two onboard L293D drivers for motors (upto 600 mA per channel)..

9. Dual 7805 Voltage regulator. 10. Dual power input options (Through molex connector or through DC Jack). 11. Two programmable Micro-Switches.

12. Two programmable LEDs. 13. Two DPDT switches (one for power on/off and one for reset).

14. MAX 232 Level shifter for RS232 communication. 15. One 3x1 Pin relimate header for RS2332 communication. 17. Four 8 Pin berg stick headers (male) from each port of ATmega16/32.

18.Wide input power range from 7 volts to 24 volts at 1.5-2 Amps. 19. Board size of 6 x 3 inches, designed for educational and hobby purpose, on high quality PCB.

8.4 Software used for Coding

The software used for coding is BASCOM AVR. It is the original Windows BASIC

COMPILER for the AVR family. It is designed to run on W95/W98/NT/W2000/XP.

The following are some the key benefits of using this software:

Structured BASIC with labels.

Structured programming with IF-THEN-ELSE-END IF, DO-LOOP, WHILE-WEND,

SELECT- CASE.

Fast machine code instead of interpreted code.

Variables and labels can be as long as 32 characters.

42

Bit, Byte, Integer, Word, Long, Single and String variables.

Compiled programs work with all AVR microprocessors that have internal memory.

Statements are highly compatible with Microsofts VB/QB. Special commands for

LCD-displays, I2C chips and 1WIRE chips, PC keyboard, matrix keyboard, RC5

reception.

AT keyboard support, send IR remote code, SPI protocol master & slave, graphical

LCD support.

Local variables, user functions, library support.

Integrated terminal emulator with download option.

Integrated simulator for testing. Or use AVR Studio and toggle between the BASIC

code and object/asm code.

Integrated ISP programmer (application note AVR910.ASM).

Many Integrated programmers like the STK200, STK300, STK500, SE, Hotchip, and

Futurelec.

Editor with statement highlighting.

Context sensitive help.

Perfectly matches the DT006 Simm-Stick

DEMO version compiles 2KB of code.

Well suited for the AT90S2313.

Ideal tool for your first steps into Micro's.

Support for TCP/IP.

43

8.5 Programming

The following code has been used in this project:

$regfile "m32def.dat"

$crystal = 1000000

Config Lcd = 16 * 2 Config Lcdpin = Pin , Db4 = Portb.4 , Db5 = Portb.5 , Db6 = Portb.6 , Db7 = Portb.7 , E = Portb.3 , Rs = Portb.2 Config Adc = Single , Prescaler = Auto , Reference = Avcc Start Adc Config Timer1 = Pwm , Pwm = 8 , Prescale = 1 , Compare A Pwm = Clear Down , Compare B Pwm = Clear Down Start Timer1 Config Porta = Input Config Portd.0 = Output Config Portd.1 = Output Config Portd.2 = Output Config Portc.0 = Output Config Portc.1 = Output Dim A As Integer Dim B As Integer Dim C As Integer Start Adc Do Reset Portc.1 Waitus 10.305 Reset Portc.0 Waitms .1 A = Getadc(0) Lcd A Lcd " " B = Getadc(1) Lcd B Lcd " " C = Getadc(2) Lcd C

44

Cls If A > 300 And B > 300 Then Set Portd.1 Reset Portd.0 Elseif A > 300 And B < 300 Then Set Portd.0 Reset Portd.1 Elseif A < 300 And B > 300 Then Set Portd.1 Reset Portd.0 Elseif A < 300 And B < 300 Then Reset Portd.0 Reset Portd.1 End If If A > 300 And B > 300 And C > 1000 Then Reset Portd.2 Elseif A > 300 And B > 300 And C < 1000 Then Set Portd.2 End If If A > 300 And B < 300 And C > 1000 Then Reset Portd.2 Elseif A > 300 And B < 300 And C < 1000 Then Set Portd.2 End If If A < 300 And B > 300 And C > 1000 Then Reset Portd.2 Elseif A < 300 And B > 300 And C < 1000 Then Set Portd.2 End If If A < 300 And B < 300 Then Set Portd.2 End If Set Portc.1 Waitus 10.305 Set Portc.0 Waitms .1 Loop

To develop an understanding of this code on can go through the BASCOM AVR tutorial

which is available online and can be downloaded very easily.

45

Chapter 9

Hybrid Operation

9.1 Introduction

The circuit consists of three project boards, a solar panel, a small fan connected to the shaft

of a DC motor which acts as the wind turbine, few MOSFETs, one operational amplifier, a

microcontroller, a boost converter, two buck converters and some other necessary

components such as resistors, capacitors and inductors. The basic idea of this project is to

utilize the best source among the two and use it to charge a battery and supply current to a

load. For efficient performance it has been ensured that when the battery is fully charged,

current is fed directly from one of the sources to the load. When none of the sources are

available but the battery has been charged to some extent for use then current is fed from the

battery to the load. All these operations have been performed by the microcontroller. The

picture below gives an idea of the project as a whole.

Figure 9.1: Circuit Photo

46

9.2 Circuit Diagram and Operation

It has been discussed earlier that the title hybrid has been given since more than one source

of different type has been used for production of current. Lets now try and look more deeply

into the circuit and understand the operation of purpose of it. The diagram below shows how

various components along with the two renewable sources are connected.

Figure 9.2: Circuit Diagram of the Hybrid System

47

Selection of the Source: The two sources are connected to the ADC of the microcontroller

and also to the input of the operational amplifier. The code of the microcontroller has been

set in such a way so that it allows the voltage from one of the sources to the operational

amplifier only when it is greater than around 1.47V. The purpose of IRF540N which is the n-

channel depletion type mosfet is to serve as switches in all parts of the circuit. In the

diagram, it can be seen two IRF540N is connected with the positive terminal of the solar

panel and wind turbine before they are connected to the positive input terminal of the

operational amplifier. This has been done for switching purpose. When the ADC of the

microcontroller reads a voltage greater than 1.47V it sends a pulse to the gate of the

corresponding MOSFET. For instance, if the voltage supplied by the solar panel is 1.5V

while the wind turbine is not rotating, than the microcontroller sends a 5V pulse to the gate of

the MOSFET which is connected to the positive terminal of the solar panel. When the pulse

has been provided, current flows from source to drain and thus that path has been shorted.

This is how switching is done.

The basic idea is to choose the most efficient source among the two. Whenever the word

efficient comes to mind, one would think of the source that provides greater voltage.

However, in this project one of the drawbacks of the solar panel is that the current provided

by it is quite less compared to that provided by the wind turbine system. Therefore, the code

has been set in a way so that the microcontroller chooses wind as the source of supply

whenever it provides a voltage greater than 1.47V. This will be explained in details later on.

Use of Adapter and LM7805: The use of adapter is to ensure the supply the supply of voltage

to the microcontroller and the biasing voltage to the operational amplifier. However, a 12V

DC adapter has been used, which is suitable for biasing of the Op-Amp but not suitable as the

Vcc of the microcontroller. For this purpose the buck regulator LM7805 has been used which

regulates the voltage to 5V. It has also been used to regulate the output of the Op-Amp to 5V.

Operational Amplifier for step-up operation: Although boost converters are usually used for

step-up operation, in that could not be used. This is due to the fact the current provided by the

solar panel is very low. From the operation of boost converter we know that it can amplify a

DC voltage, but the output current decreases. A minimum current also needs to be provided

48

as the input current to ensure that a boost converter works. Even though the boost converter

may work when the wind turbine is working as the source, but whenever the solar panel is

working the current is too low for the boost converter to work. Although, this problem could

have been solved by providing a pulse of smaller time period to the base of the transistor

used in the boost circuit, this couldnt be done due to the limitation of our microcontroller.

A suitable and economic solution to this problem is the use of IC741 which is the operational

amplifier. Although, this is not a suitable solution when a system is to be designed for

producing high voltages, but for a prototype this turned out to be suitable solution.

The operation of the Op-Amp as a non-inverting amplifier has been applied to this problem.

One resistor of 1K connected to the negative input terminal and one 10K connected

between the output and negative input terminal ensured a gain of 11 times that of the input

voltage. The only problem of using Op-Amp is that current flowing is about 17mA and this

increases the time taken by the battery to store charge. Since the output provided by the Op-

Amp is a minimum of around 10V so a buck regulator has been used again to ensure that no

harm is done to the battery during the process of charging.

Use of Boost Converter: In most charging system, a Charger light for instance, during the

charging of the battery the load cannot be on. In this prototype system, the charging of

battery and the load being on happens simultaneously. This is mainly because of the use of

the boost regulator. It has been stated earlier that the use of boost regulator isnt possible

because of the lack of the flow of current from the solar panel. So the question that comes to

mind is how come the boost regulator is coming to use now? Well, this can be explained

easily if we take a close look at a certain portion of the circuit.

49

Figure 9.3: A close look at the circuit

Figure 9.4: A closer look at the circuit board

50

If we look at the current flowing, we get an idea of what is happening here. The LM7805 is

the regulator that regulates the output from the Op-Amp. This voltage is used for charging

the battery and also as the input of the boost regulator. As the battery starts to store charge, a

current tries to flow in the opposite direction. A diode placed right after the regulator stops

the current from flowing in the opposite direction and forces it to flow in the direction shown

in the diagram. The current marked IB is the current from the battery, and IR is the current

from the renewable source, these two currents are added together as IB+R and flows through

the boost converter circuit. Thus, it can be concluded that the current has been increased and

now the boost regulator works successfully. So, this is how the boost regulator has been

made to work using the current from both the rechargeable battery as well as the renewable

source. This also ensures that the charging of battery and the load remaining on happens at

the same time. From experimental analysis it has been found out that the regulated output of

the boost converter is in the range 13V-16V.

Various functions of ATMEGA32: The microcontroller uses BASCOM AVR code. The code

has been shown in of the earlier chapters. The various functions of the microcontroller will

now be discussed.

The first basic operation is to choose the most efficient source of the two. This has already

been discussed in the topic Selection of the Source. Three MOSFETs and one BJT have

been used in this project. Thus, another function of the microcontroller is to send pulses to

these transistors as per requirement.

Earlier in this chapter, it has been mentioned that there is a limitation of the microcontroller

ATMEGA32 which doesnt allow us to reduce the time period of the pulses. The limitation is

that the microcontroller cannot send pulses in nanoseconds. Had this been possible, it would

have allowed the use of boost regulator in place of the Op-Amp.

Use of BJT: Although, MOSFET could have been used in the boost converter circuit, but

MOSFET is a voltage controlled device, whereas, BJT is a current controlled device. In

addition, the switching time of BJT is fast compared to that MOSFET, thus in this project

BJT was preferred to MOSFET in the boost converter circuit.

51

9.3 Four Main Operations

The whole project had to be verified experimentally many times to ensure that all the

components were working successfully especially the microcontroller. Since, the practical

world always presents us with many factors which are neglected in the theoretical world, in

the initial stages there were many unexplainable errors. However, after repeating the analysis

many times we were successfully able to build a prototype whose operation has already been

described. Lets now summarize the four main operations of our project with pictures and

data tables. These are the four main operations:

i) Charging of battery and feeding current to load using wind energy

ii) Charging of battery and feeding current to load using solar energy

iii) Current fed to the load directly from renewable source

iv) Current fed to the load directly from battery

9.4 Charging of battery using wind energy feeding current to load using

wind energy

When the voltage from the generator is greater than the voltage from the solar panel then the

battery is charged using wind power. However, in this project, the solar panel is a bit weak.

The solar panel is weak in a sense that it provides with less current compared to that of wind,

even if the voltage provided by it is comparable or greater than that of wind. Thus, whenever

sufficient wind energy is available the microcontroller chooses wind over solar. This

operation is fairly simple and can be done by connecting the positive terminal of the inputs to

ADC pins of the microcontroller. The microcontroller converts the analog voltage to a digital

value and compares the input from wind and solar. This operation goes on as long as

sufficient wind energy is available and battery needs to be charged. In addition, the load also

draws current from the wind power.

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Figure 9.5: Charging of battery using wind energy

Figure 9.6: A photo of the system utilizing wind energy

9.5 Charging of battery and feeding current to load using solar energy

Although, the microcontroller is supposed to perform this operation whenever the voltage

provided by the solar panel is higher than that provided by the wind, in practice the

Wind Turbine Battery Load

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Battery Load Solar Panel

microcontroller has been programmed such that it allows the charging of battery by solar

energy only when wind energy isnt available in sufficient amount. This has been done to

ensure efficient performance since the solar panel is a bit weak when it comes to providing

current. The operation is similar to that mentioned in one of the pervious chapter. Once

again, the ADC pin comes into use and current is also fed to the load.

Figure 9.7: Charging of battery and feeding current to load using solar energy

Figure 9.8: A photo of the system utilizing solar energy (wind turbine not rotating)

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9.6 Current fed to the load directly from renewable source

To ensure efficient performance of the system this operation has been added. It ensures that

when the battery is fully charged, the charging path is open so that the battery charging

process is stopped. Then the load only draws current from one of the source. Once again, this

is done by connecting the positive terminal of the battery to one of the ADC pins of the

microcontroller. Whenever, the microcontroller reads that the battery is fully charged it

disconnects the charging path by turning of the pulse that was going to the MOSFET.

However, it must be mentioned that once the battery charging path has been forced to be

open using the MOSFET as switch, the boost regulator no longer works. This is because of

the fact that during the charging process the battery contributes some of its current to the load

and this current is added to a portion of the current coming from the renewable energy. Thus,

when the charging process is stopped there is no longer a contribution of current by the

battery. So, the earlier problem of not having enough current causes the same problem again.

In this situation, one possible improvement that could have been made to this circuit was

connecting two renewable sources in series. However, this wasnt done owing to the fact that

the solar panel has an opposing current flowing in situation when there is no light, which

meant that more MOSFETs had to be used.

Figure 9.9: Current fed to the load directly from renewable source

Solar Panel

Wind Turbine

Load

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9.7 Current fed to the load directly from battery:

This particular operation comes into use when none of the sources are available. If the battery

is fully or sufficiently charged then the microcontroller sends pulse to one of the MOSFETs

which short a path connecting the battery and the load. This ensures that the load remains on

all the time.

9.8 Experimental Analysis

After practically testing the design several times we were successfully able to build a

prototype of a simple power system. Below are some of the readings that were noted during

the experiment.

Expt. No.

Wind Turbine Solar Panel

Source Chosen

Boost Converter output

Battery Charging

Load

(i) 0V 2V Solar 14.5V On On

(ii) 4.5V X Wind 15 On On

(iii) 4.5V X Wind Drop Across the Load Full(4.88V) On

(iv) 1V 2V Solar Drop Across the Load Full(4.88V) On

(v) 0V 0V None 16V Off On

(vi) 0V 0V None 0V Off Off

Figure 9.10: Experimental Data

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It is important to note that in (iii) and (iv) when the battery is fully charged the boost

regulator doesnt work due to the fact that the current provided isnt high enough. Does the

voltage read is the drop across the load.

In (v) none of the sources are available; this is when the load is fed directly from the battery.

No charging of battery is possible in this case.

In (vi) none of the sources are available, the battery has run out of charge and thus the system

comes to a halt with both charging and load being off.

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Chapter 10

Discussion and Conclusion

10.1 Discussions

This project presented some major difficulties one of which was the use of buck boost

converter. Although, ready made buck boost converters are available in markets at present,

but in our country these converters are not available neither are boost converters. Thus, the

decision to use operational amplifier which is the IC-741 was taken. This served for the boost

operation. LM7805 and LM7812 which regulates voltage to 5V and 12V respectively were

bought. For both LM7805 and LM7812 the input voltages to the chip must be greater than 5

and 12 volts respectively or else the circuit will not work.

The use of operational amplifier introduced one of the major drawbacks of this project which

is the fact that it doesnt allow a great amount of current to flow through. Experimental

analysis shows that only a current of approximately 16mA could flow. This is a huge

problem since it increases the time taken by the battery to complete the charging process. In

addition, some loads that require higher current than 16mA could not be used properly in our

circuit. For example, an energy saving bulb that requires 12V and a current of 2A was

connected in our circuit but its brightness was minimum due to the lack of flow of current.

The use of diode is essential in the charging circuit which ensures that current doesnt flow in

the opposite direction, that is, from battery towards the regulator. In similar situations, where

the flow of current in a particular direction was to be avoided, a diode was used.

The use of OPAMP forced the use of some extra voltage sources for biasing which increased

the cost of this particular circuit. A simple to this problem once again is the use of a boost

regulator.

Negative biasing was provided simply by connecting the positive terminal of the battery to

the ground and the negative terminal to the desired pin of IC 741.

The use of boost converter with the load connected across its output was possible mainly

because of the fact the battery while charging contributes some of its current along with the

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current coming from the regulated output of the Op-Amp. This also enabled the charging

process and load being on to be possible at the same time.

10.2 Suggestions for future work

Although this type of a system is not really suited to countries where the wind speed is not

sufficient, this particular prototype can be used in small applications. One particular

application that can be suggested for future work is the use of this circuit as a portable

charger for cell phone, or source of power for devices that require 5-12V. This would be

feasible when traveling in a car or fast moving vehicle where theres always sufficient wind

and during daytime the possibility of solar power.

The second suggestion for future work is the possible use of a third source. Sound energy is

one possible source that can be used. The only problem with using sound energy is that it

produces very less voltage for a very loud sound. Experimental analysis shows that

piezoelectric crystals are materials capable of turning mechanical energy into electrical

energy. A prototype of a particular technology was able to convert sound of around 100

decibels - the equivalent of noisy traffic - to generate 50 mill volt of electricity. The

technology uses tiny strands of zinc oxide sandwiched between two electrodes. A sound

absorbing pad on top vibrates when sound waves hit it, causing the tiny zinc oxide wires to

compress and release. This movement generates an electrical current that can then be used to

charge a battery. In our project we tried using a microphone to generate electricity from a

sound source; however, very loud sound was required. We played loud music from the

speakers of a computer and held the microphone near the speaker. Approximately 30mV was

generated, this was later on amplified to about 3V using an operational amplifier, majority of

which was due to noise. So, the use of sound energy as the third source is definitely possible

but needs a lot of research to be done.

Another proposal for future work is probably is the most interesting of all. In recent times, in

our country the use of Electric Vehicle has been quite popular. It uses electricity with the

help of a battery system to start its engine. However, during the charging process of these

batteries they consume a huge amount of power from the grid. The prototype used in this

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project with a few changes to it can turn out to be a very suitable system for these types of

vehicles and can also save huge amount of power from the grid.

10.3 Conclusion

Its very difficult to remove the losses from a power system. Thus, a better method of

improving things would be to try and utilize the energy that is being wasted. Its not

necessary to use that waste energy and utilize it to generate voltage in huge amount; rather,

we can try and use them in many small applications. That way its possible to reduce

increasing demand of electricity from the National Grid.

With our prototype, we have successfully charged various mobile phones. The size of our

prototype is very small and easily portable. The output was boosted to around 16V. If some

improvements are made, then it can be utilized in the use of appliances that require voltages a

bit higher than 5V.

Many people might argue that the future of A Renewable World is dark. But, from what

we have experienced after doing the project, the possibilities of utilizing renewable energy is

endless, useful and interesting.

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[6] I. Barbi, Eletrnica de Potncia, Autors Editor, 6th Edition, Florianpolis, 2006.

[7] I. Barbi, Projeto de Fontes Chaveadas, Autors Editor, 2nd Edition, Florianpolis, 2007.

[8] Wang, Z., 2-MOSFET Transistors with Extremely Low Distortion for Output Reaching

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[10] H. M. Oliveira Filho, R. P. T. Bascop, L. H. S. C. Barreto, F. L. M. Antunes, D. S.

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Battery Charging, in Proc. of INDUSCON, vol. 8, 2008.

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IRF540N (DATASHEET):

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2N3055(DATASHEET):

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LM78XX Series(DATASHEET):

Hybrid Power System

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