1

DESIGN AND SIMULATION OF DOMESTIC HYBRID

POWER SUPPLY PROJECT

By

KARANJA JAMES KIRONJI

BSEE/43352/101/DF

LABEJA CALEPS

BSEE/43534/101/DU

AUGUST 2014

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DESIGN AND SIMULATION OF DOMESTIC HYBRID

POWER SUPPLY PROJECT

Report submitted to Kampala International University in partial fulfillment

of the requirement for the award of the degree

Of

Bachelor of Science in Electrical Engineering

By

KARANJA JAMES KIRONJI

BSEE/43352/101/DF

LABEJA CALEPS

BSEE/43534/101/DU

DEPARTMENT OF ELECTRICAL AND TELECOMMUICATION ENGINEERING

SCHOOL OF ENGINEERING AND APPLIED SCIENCES

AUGUST 2014

©2014,Labeja caleps and karanja james kironji,All rights reserved.

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DECLARATION

We, KARANJA JAMES KIRONJI and LABEJA CALEPS, hereby declare that this project

report is own and original work and that it has not been presented to any other

University for similar or any other degree award.

Signature ___________________

Date__________________

Labeja Caleps

BSEE/43534/101/DU

Signature ___________________

Date__________________

Karanja James Kironji

BSEE/43352/101/DF

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CERTIFICATE OF APPROVAL

This is to certify that the work in this project report entitled “DESIGN AND

SIMULATION OF A DOMESTIC HYBRID POWER SUPPLY PROJECT” Carried

out by Karanja James Kironji and Labeja Caleps under my supervision is in partial

fulfillment of the requirement for the degree of Bachelor of Science in Electrical

Engineering at KAMPALA INTERNATIONAL UNIVERSITY.

………………………………………………….

Mr. Olanya Isaac

Project supervisor

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DEDICATION

We dedicate this work to almighty God in appreciation for this far he has brought us

and believe a brighter future lies ahead through His guidance. It is also dedicated to

our families for the support and dedication they have bestowed upon during our

entire study.

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ACKNOWLEDGEMENT

We highly appreciate the great help we received from the entire KIU society, special

thanks must go to all lecturers of the department of Electrical Engineerig led by Mr

Njubo Nelson for the knowledge and skills they helped us gain, Mr. Nurein Foum

who initiated our first field attachment setting a platform for us to gather our first-

hand experience. Mr Obedi Kiyaga the most social lecturer we have met in our

college life. We are very grateful to our supervisor Isaac Olanya for his tireless work

and maximum cooperation in supervising our research project. Thank you so much

and may God bless you.

We greatly thank Geomax Consulting Engineers, Kenya and in particular Eng. Loise

Mbaria for her facilitation during my (James) field attachment from where I acquired

relevant knowledge and information about this project.

Special thanks to our families who have played a great role in our college life our

uncles in particular Dr. Yolam Okech, Boniface Kamau, Daniel Muiruri who have

provided us with financial support through-out our college. Our Mums Janet and

Helen, My father Benny, Brothers Joshua, Ken, sisters Brenda and Ruthie Lelee who

provided us with spiritual and financial support and kept us focused.

Lastly, we sincerely thank our Grandmothers Eunice, Margret and Beatrice our

Grandfathers James and Kenneth for their personal efforts and a million dollar

advice. Our friends Helen Wanjiku, Papito Francis, Benson Waweru, Shadrack Maina,

Mary W, Beatrice Mugo, Esther Mbabazi, who were shoulders to lean on and who

stood by us when we needed friends and people to talk to. Other than that we have

really learnt from you that the value of money and happiness increases when it is

shared by many. Thank you and May God bless you all.

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ABSTRACT

This project is set out to design and simulate a domestic hybrid power supply

project. Thus the project is meant to carry out research on the integration of solar,

wind and a battery bank by interlinking them to act as a single source of power thus

providing a solution to frequent power shortages which is a common phenomenon in

the East African region. The research employed not only a design but a simulation

that provides real times results from arbitrary assumptions that act as proof that this

is achievable. Besides this, data was collected using face to face interviews; internet

based research; our project has been critically analyzed and all values used not

literal but real time values which can be used at the domestic level and thus a

voltage output of 120/240VAC a voltage that is used in the East African region.

The findings concluded that this energy sources integration is attainable and can

help curb the many power shortages. The results are evident and support the

project idea. The study conclusively recommends the implantation of this project at

domestic, commercial as well industrial level. The feed in tariffs can also be applied

trough connection to the smart Grid and thus provide power to the community as

well as the national grid.

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TABLE OF CONTENTS

DECLARATION................................................................................................................................................ii

CERTIFICATE OF APPROVAL.......................................................................................................................... iii

DEDICATION ................................................................................................................................................. iv

ACKNOWLEDGEMENT ...................................................................................................................................v

ABSTRACT.....................................................................................................................................................vi

TABLE OF CONTENTS ............................................................................................................................... vii

LIST OF FIGURES ........................................................................................................................................... ix

LIST OF TABLES ..................................................................................................................................... xi

NOMENCLATURE AND ABBREVIATIONS ..................................................................................................... xii

CHAPTER 1...................................................................................................................................................1

1.1 INTRODUCTION ..........................................................................................................................1

1.2 Problem Statement .......................................................................................................................2

1.3 SIGNIFICANCE OF THE PROJECT.............................................................................................3

1.4 MAIN OBJECTIVE ........................................................................................................................3

1.5 RESEARCH QUESTIONS..................................................................................................................4

1.6 Scope of the project ...................................................................................................................4

CHAPTER 2.....................................................................................................................................................6

LITERATURE REVIEW .....................................................................................................................................6

2.1 Introduction...................................................................................................................................6

2.2 Photovoltaic (PV) Power System...................................................................................................8

2.21 Photovoltaic cell. .......................................................................................................................9

2.22 Photovoltaic module: ................................................................................................................9

2.23 Photovoltaic array: ..................................................................................................................10

2.3 Wind Turbine Power System.......................................................................................................12

2.3.1 Wind into watts..........................................................................................................................13

2.4 Power Electronic Circuit ...........................................................................................................16

2.3.1 AC-DC Rectifier ..................................................................................................................17

2.3.2 Inverter...............................................................................................................................17

2.3.3 DC-DC Converter Analysis. ..............................................................................................18

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2.5 Hybrid Wind and Photovoltaic Power System.......................................................................19

2.6 Conclusion ..................................................................................................................................20

CHAPTER 3...................................................................................................................................................21

METHODOLOGY, DESIGN AND IMPLEMENTATION.........................................................................21

3.1 Introduction ...............................................................................................................................21

3.2 Modeling of Photovoltaic Power System................................................................................21

3.3 Modeling of Wind Turbine Power System .............................................................................24

3.4 Model of Battery Circuit............................................................................................................29

3.5 Modeling of AC-DC Rectifier ....................................................................................................31

3.6 Inverter model...........................................................................................................................32

3.7 spwm technique ........................................................................................................................32

3.8 Modeling of Hybrid System with battery storage.................................................................34

CHAPTER 4.................................................................................................................................................36

SIMULATION RESULTS AND DISCUSSIONS .....................................................................................36

4.1 Introduction ...............................................................................................................................36

4.2 Photovoltaic Model Simulation ................................................................................................36

4.3 Wind model simulation.............................................................................................................40

CHAPTER 5.................................................................................................................................................44

CONCLUSIONS AND RECOMMENDATIONS.......................................................................................44

5.1 Conclusions ................................................................................................................................44

5.2 Recommendations.....................................................................................................................44

REFERENCES ................................................................................................................................................45

Bibliography.................................................................................................... Error! Bookmark not defined.

Appendix I....................................................................................................................................................48

Appendix II...................................................................................................................................................49

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LIST OF FIGURES

Figure 2.1: Photovoltaic cell, module and Array…………………………………………………………21

Figure 2.2: Schematic block of a PV cell…………………………………………………………………..22

Figure 2.3: Simplified circuit diagram of a PV cell……………………………………………………….23

Figure 2.4: typical I-V characteristics of solar panel…………………………………………………….24

Figure 2.5: typical P-V characteristics of a solar panel…………………………………………………24

Figure 2.6: A plot of wind output power (Kw) against wind speed (m/s)……………………….27

Figure 2.7: PMSM Operation mode………………………………………………………………………………28

Figure 2.8: Three phase full wave bridge rectifier………………………………………………………….30

Figure 2.9: Igbt-diode inverter…………………………………………………………………………………….31

Figure 2.10: Basic buck converter……………………………………………………………………………..…31

Figure 2.11: proposed design for the Hybrid power project........................................32

Figure 3.1: characteristic PV cell………………………………………………………………………………….35

Figure 3.2: Simulink model of a photovoltaic solar cell…………………………………………………..36

Figure 3.3: PV cell standalone connected to the Load through battery storage…………………37

Figure 3.4: Simulink wind turbine model and its respective parameter...............................38

Figure 3.5: Turbine output power Vs Turbine speed.........................................................39

Figure 3.6: Wind turbine block model.............................................................................40

Figure 3.7: Cp (λ, β) block model...................................................................................40

Figure 3.8: Wind turbine, 2 mass drive Train and PMSM block model................................41

Figure 3.9: Equivalent circuit of battery and I-V characteristic graph..............................42

Figure 3.10: Simulink model of the battery circuit............................................................43

Figure 3.11: Battery discharge characteristics...........................................................44

Figure 3.12: Rectifier block parameters..........................................................................45

Figure 3.13: Inverter Model...........................................................................................46

Figure 3.14: PWM Generator Parameters........................................................................47

Figure 3.15: Buck converter model in Simulink................................................................47

Figure 3.15: Standalone Wind power system connected to load........................................48

Figure 3.17: Stand-Alone Hybrid Project.................................................................49

Figure 4.1 (a) at 400W/m2............................................................................................51

Figure 4.1 (b) at 600W/m2.............................................................................................51

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Figure 4.1 (c) at 1000W/m2......................................................................................52

Figure 4.2: P-V characteristics……………………………………………………………………………………55

Figure 4.3: P-I characteristics…………………………………………………………………………………….55

Figure 4.4: voltage and Current out-puts of a wind generator respectively………………..……56

Figure 4.5: Buck Converter Voltage and Current Output…………………………………………………57

Figure 4.6 (a): PV output at the Load …………………………………………………………………………58

Figure 4.6 (b): Wind Turbine output at the Load…………………………………………………………..59

Figure 4.7: output voltage waveform of the hybrid system…………….………………………………5

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LIST OF TABLES

Table 2.1: wind speed Vs output power……………………………………………………………….28

Table 3.1: parameters of lead acid battery……………………………………………………………44

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NOMENCLATURE AND ABBREVIATIONS

AC - Alternating Current

DC - Direct Current

IGBT - Insulated Gate Bipolar Transistor

G - Solar Irradiance

MW - Megawatts

PMSG - Permanent Magnet Synchronous Generator

PMSM - Permanent Magnet Synchronous Machine

PV - Photovoltaic

PWM - Pulse Width Modulation

RPM - Revolution Per Minute

SCR - Silicon-Controlled Rectifier

STC - Standard Test Conditions

T - Temperature

VSC - Voltage Source Converter

FYP - Final Year Project

Cp - Power Coefficient

Im - Photovoltaic Current Output

Impp - Maximum Power Current

Io - Saturation Current

Ipv - Photovoltaic Current

Isc - Short-Circuit Current

KI - Short-Circuit Current/Temperature Coefficient

Kv - Open-Circuit Voltage/Temperature Coefficient

PG - Power at Generation Side

Pwb - Wind Turbine Output Power

Tm - Wind Turbine Output Torque

Vmpp - Maximum Power Voltage

Voc - Open-Circuit Voltage

Λ - Speed Ratio

Β - Blade Pitch Angle

ρ - Air Density

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BB - Battery bank

LPG - Low Power Generator

Tm - Mechanical torque applied to rotor

Tem - Electromagnetic torque applied by generator to rotor

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CHAPTER 1

1.1 INTRODUCTION

Definition of terms

Irradiance- This the flux of radiant energy per unit area (normal to the direction of

flow of radiant energy)

Autonomy- This the period of time that a battery can supply power to loads

without getting further recharged.

Solar Array- A set of solar voltaic modules connected and mounted on a supporting

structure.

Simulation- This is the imitation of the operation of a real process or system over

time through a computer.

Turbine- This is a rotary mechanical device that extracts energy from moving fluids.

Fossil- These are fuels that are formed by natural processes such as anaerobic

decomposition of buried dead organisms.

Stand-alone - A system able to operate independently of other hardware or

software.

Obsolete- To become of no- longer use.

Bus-bar- A conducting metal that carries heavy currents to supply to several

circuits.

Start-up wind speed - the wind speed that will turn an unloaded rotor.

Cut-in wind speed – the wind speed at which the rotor can be loaded.

Rated wind speed – the wind speed at which the machine is designed to run.

(This is at optimum tip-speed ratio)

Furling wind speed – the wind speed at which the machine will be turned out of

the wind to prevent damage

Maximum design wind speed – the wind speed above which damage could occur

to the machine

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1.2 Problem Statement

The continuous instability of fossil fuel prices, the amount of oil and natural gas

reserves is getting lesser and the serious environmental degradation due to over-

exploitation of existing energy reserves are among the reasons to develop an

alternative energy generation system that based on renewable energy sources, such

as a hybrid system that combined solar and wind energy.

Although the solar and wind energy are known as dependable and widely available

renewable energy sources in east Africa, but the intermittent energy sources will

cause the power generator to produce a fluctuating output. For example, we could

not generate energy using a standalone PV system at night or during a cloudy day

because there is no solar radiation. Similarly, the varying wind speed will affect the

amount of energy generated by a standalone wind turbine system. . In other words,

both standalone systems don’t present desirable efficiency in generating energy.

This instability output voltage may cause serious problem to certain electronic

devices such as induction motor or variable speed drives that need a constant supply

for continuous processing, as well as lights which have ballasts. The consequences

vary with industry, but loss of production often relates to profitability or sometimes

personnel safety. Hence, in this project an energy storage system battery was

introduced into the hybrid wind and photovoltaic power generation system. The

added energy storage will store energy during low load demand period and helps to

stabilize the system generated output voltage.

To have only one energy/power source is expensive. The main objective of this

research is to integrate the two or more energy sources into one system and

enhance the utilization of the existing power grid such that, even if one source is off

or faulty, the other source(s) keeps the grid operational/running.

In most third world countries which has a major power source that monopolizes the

economy, power outage is unavoidable, This may either be due to faults or system

break down. Exploitation of renewable sources like solar and wind in a large scale

and incorporating them to the main grid solves the above problem.

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1.3 SIGNIFICANCE OF THE PROJECT

Through this project we have been met with constrains that we have beaten,

limitations that almost made us change the project design and the whole project as

whole. We feel this is a great achievement running a simulation and gives an output

as close as the real output of an implemented system is a milestone.

This project sets a platform ready for implementation and future research to the

project refinement and provision of a smarter grid domestic system through the use

of micro-controllers and power factor correction banks. This country has long

embattled power failure and the implementation of this project design at any given

besides it cost constrains can really be of great importance.

This region has a lot of potential in terms of renewable source energy potential that

has been left untapped. We feel further research and investment in the energy

sector would present a golden opportunity to not only the researchers themselves

but to the citizens of this country through a more stable power supply, fuelling the

development of their businesses.

1.4 MAIN OBJECTIVE

The main objective of the project is;

To carry out a research based project on the integration of solar, wind and a battery

bank by interlinking them to act as a single source of power. This project on a large

scale aspect can be considered a national system in feed-in tariff rates for these

forms of energy thus providing a source of efficient, stable and sustainable power.

Through this project we intend to have comprehensive results that encourage

provision of incentives in the implementation of similar projects. The design and

simulation of results gives an output that displays a standing ovation project.

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1.5 RESEARCH QUESTIONS

Which is the most economical system for short distance as well as distribution, AC or

DC?

Is the stand-alone energy production more effective than a hybrid system in which

case each source having its own storage (battery bank)?

Are Uganda’s wind-speeds ideal for power production and what speed is best to

achieve a power output of 1kW using a 3m rotor diameter?

What is the average mean-time in Uganda sunshine to achieve an irradiance of

1000W/ m2?

Is a wind power output and direct load connection achievable without creating a

system disturbance especially the battery buffering and different potential

differences due to the power input from the battery?

1.6 Scope of the project

This project revolves around uninterrupted power system, in which case we as a

team worked on a project whose power output will be a reliable. Given that we have

a battery system that can be inverted to give a power output most suitable to many

domestic appliances: television sets, LED lights, small motors among others.

Given the research and simulations this project is solely dependent on our

innovativeness and applications from the units covered during our course at this

institution. Thus MATLAB and Simulink are the major drives that catapulted the

successful delivery of this project. All assumptions: wind speeds, irradiance the ideal

PV cell are through comprehensive research and discussions with companies who

have done this projects or similar projects in the recent past. We find it important to

point out that this (hybrid) project is of its kind here in Uganda and Kenya because

none of the companies have implemented it so far.

We faced a number of problems while modeling this system and the other

components in our system in the Simulink window of the MATLAB. It was learning

process for us. So, we felt the need to discuss those issues and sum up our critical

observations:

5

Computation of bus power, load power and the battery output power was vital. This

led to us changing the whole design of our system as we realized we could not

connect the windmill to the same AC bus bar as the inverted power from our Battery

bank.

Consequently we had to change the system parameters this led to an additional

20hrs of labour to navigate through this problem.

Given we live far apart time allocation to meet our deadlines was crucial and a great

strain to our planned schedule of works.

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Since the beginning of power system development, the electricity is supplied to the

users in a model of bulk-power transmission system. As the technologies in power

system improve, the traditional power system operating models appear to be

becoming obsolete. As a result some disadvantages in terms of security and

flexibility are observed. Moreover, fluctuation of fossil fuels price and generating

electricity with fossil fuel will cause pollution to the environment. Therefore to

overcome the problems and to improve the power supply quality, the distributed

generation (DG) based on green energy such in this case, solar and wind. These two

sources are keenly observed and taken into consideration as an alternative way to

generate and supply power energy to users.

The world of today is dynamic and the need to have a clean safe energy has become

an important aspect in energy development. Our project idea and growth is based

on realizing a sustainable energy source for realistic economic growth. Africa has a

high potential in hybrid power projects given its wide pool of renewable energy

sources. With our project idea we look forward to coming up with a realistic project

that solely relies on renewable sources of energy earlier mentioned. However, the

main objective being the use of this sources of energy over conventional ones.

A Hybrid Energy System incorporates various energy infrastructures covering most

inhabited areas. It comprises three stages:

Production: The production of electricity in the power farm.

Integration: It forms the most important part of this project as it brings to life the

combination of various energy systems to a single platform.

Converter and inverter points: this system has both AC and DC links which need

to be transformed from direct to alternating current and/ or vice versa.

A typical hybrid system combines two or more energy sources, from renewable

energy technologies, such as photovoltaic panels, wind or small hydro turbines; and

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from conventional technologies, usually diesel or LPG gensets (though biomass fed

gensets are also a feasible option, if locally available). In addition, it includes power

electronics and electricity storage batteries.

The hybrid system can be designed following different configurations to effectively

use the locally available renewable energy sources and to serve ALL power

appliances (requiring DC or AC electricity). The technological configurations can be

classified according to the voltage they are coupled with; this is, using DC, AC and

mixed (DC and AC) bus lines.

Principle technological configurations for hybrid systems;

• Electricity generation coupled at a DC bus line

All electricity generating components are connected to a DC bus line from which the

battery is charged. AC generating components need an AC/DC converter. The

battery, controlled and protected from over charge and discharge by a charge

controller, then supplies power to the DC loads in response to the demand. AC loads

can be optionally supplied by an inverter.

• Electricity generation coupled at AC bus line

All electricity generating components are connected to an AC bus line. AC generating

components may be directly connected to the AC bus line or may need a AC/AC

converter to enable stable coupling of the components. In both options, a

bidirectional master inverter controls the energy supply for the AC loads and the

battery charging. DC loads can be optionally supplied by the battery.

• Electricity generation coupled at AC/DC bus lines

DC and AC electricity generating components are connected at both sides of a

master inverter, which controls the energy supply of the AC loads. DC loads can be

optionally supplied by the battery. On the AC bus line, AC generating components

may be directly connected to the AC bus line or may need an AC/AC converter to

enable stable coupling of the components.

Solar and wind are intermittent energy sources as they vary over time and do not

usually meet load demands at all times. Among these two types of renewable

energy, wind is the more affected source compare to photovoltaic due to its

variability. Similarly, the photovoltaic system also depends on the weather conditions

and only can operate during day-time. These two unpredictable energy sources

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stand-alone system will produce fluctuated output energy and thus cannot ensure

the minimum level of power continuity required by the load. A hybrid system is

defined as the combination of two or more types of electricity generation system. In

this project, PV system is combining with wind turbine system to form a renewable

energy hybrid system. Since the output of these renewable energy is greatly

depends on climatic conditions such as solar irradiance, wind speed, temperature

among others, the instability of the system output is compensated by adding a

suitable energy storage system to the hybrid system such as a battery bank (BB).

This is to ensure a perfect balance exist between power demand and generated

power.

The advantages of using renewable energy sources based hybrid systems are it

increases the reliability of the hybrid system because it is based on more than one

electricity generation source. Besides that, it is a pollution free and environmental

friendly system as it does not use any fossil fuel. The solar energy also becomes one

of the most promising alternatives for conventional energy sources and has been

increasingly used to generate electric power from sunshine. Moreover, the hybrid

system is suitable to use in remote areas with no access to utility grid.However,

there is also disadvantage of using hybrid systems such as in most cases the system

is over- sized because it contains different types of power generation system.

This chapter presents information about the background studied on PV power

system, wind power system, hybrid power and also the AC-DC rectifier. It gives an

overall idea on developing and modeling the hybrid system and the energy storage

system.

2.2 Photovoltaic (PV) Power System

PV power system converts sunlight into electricity. The basic unit of a photovoltaic

power system is the PV cell, where cells may be grouped to form panels or modules.

The panels then can be grouped to form large photovoltaic array that connected in

series or parallel, as shown in Figure 2.1. Panels connected in parallel increase the

current and connected in series provide a greater output voltage.

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Figure 2.1: Photovoltaic cell, module and Array.

2.21 Photovoltaic cell.

The solar cells are made from semiconductor materials that able to generate electric

current when being exposed to sunlight radiation. When a photon (particle of light)

strikes a photovoltaic cell, some of the energy it brings is captured by the

semiconductor material. That energy knocks electron loose, allowing them to flow

freely. Electric fields created between the positive layer (P-type) and the negative

layer (N-type) of the cells then force the loose electrons to go in certain direction

through a connecting wire as direct current (DC) electricity.

2.22 Photovoltaic module:

The voltage generated by a single solar cell is very low, around 0.5V. So, a number

of solar cells are connected in both series and parallel connections to achieve the

desired output. In case of partial shading, diodes may be needed to avoid reverse

current in the array. Good ventilation behind the solar panels is provided to avoid

the possibility of less efficiency at high temperatures.

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2.23 Photovoltaic array:

Again the power produced by a single module is not sufficient to meet the power

demands for most of the practical purposes. PV arrays can use inverters to convert

the dc output into ac and use it for motors, lighting and other loads. The modules

are connected in series for more voltage rating and then in parallel to meet the

current specifications.

Figure 2.2: Schematic block of a PV cell.

Figure 2.3: Simplified circuit diagram of a PV cell.

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The photovoltaic cell output voltage is basically a function of the photocurrent which

is mainly determined by load current depending on the solar irradiation level during

the operation

Vc = (A*k*Tc/e)ln ((Iph+I0-Ic)/I0) - Rs*Ic

The symbols used are;

Vc: cell output voltage, V.

Tc: reference cell operating temperature (20 °C).

Rs: series resistance of cell (0.001 Ω).

Iph: photocurrent, function of irradiation level and junction temperature (5 A).

I0: reverse saturation current of the diode (2*10-4 A).

Ic: cell output current, A.

k: Boltzmann constant (1.38 × 10-23 J/K).

e: electron

Figure 2.4: typical I-V characteristics of solar panel.

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Figure 2.5: typical P-V characteristics of a solar panel

2.3 Wind Turbine Power System

Wind turbines that generate electricity operate in much the same way as a

hydroelectric generating station. Instead of falling water, wind turbines use the

kinetic energy of blowing air to spin the blades of the turbine which are connected to

a generator. Wind power is expected to be a leading power source in Denmark

provide more than fifty per cent of its current 16 per cent of it national grid by 2020.

In the East Africa region, Kenya has invested heavily to see the growth of current

wind power of 500MW to 2050MW by 2030 making it the country’s biggest

investment of $800 million. This project is commonly known as the Lake Turkana

wind power project (LTWP).

Wind power is the fastest growing energy source in the world and it will be playing

an increasing role in supplying our electricity. The amount of electricity a wind

turbine can produce depends on the strength and consistency of the wind at any

given time. Generally, the wind needs to be blowing at 14 km/ hr. for a wind turbine

to start producing electricity. With increasing wind speed, the power output

increases to a maximum at 50 km/hr.

Most types of power plants can run 24 hours a day. However, wind turbines can only

generate electricity when the wind is strong enough. Typically the wind is stronger

13

at night than during the day and also stronger in winter than summer. Because of

this, wind turbines cannot always be relied on to help meet peak electricity demand.

The requirements for this system were identified before thus this section will majorly

deal with the interconnection of these forms of energy. At any given time this

system should work towards the use of renewable sources of energy thus will do

away as much as possible with other energy sources as well as maximization to the

later of extra units produced being sold out to potential customers within the farms

locality. It is therefore important at this juncture to point out our system is based on

energy saving as well as the conservation of the environment.

There are various important wind speeds to consider:

Start-up wind speed - the wind speed that will turn an unloaded rotor.

Cut-in wind speed – the wind speed at which the rotor can be loaded.

Rated wind speed – the wind speed at which the machine is designed to run.

(This is at optimum tip-speed ratio).

Furling wind speed – the wind speed at which the machine will be turned out

of the wind to prevent damage.

Maximum design wind speed – the wind speed above which damage could

occur to the machine.

2.3.1 Wind into watts

Although the power equation above gives us the power in the wind, the actual

power that we can extract from the wind is significantly less than this figure

suggests. The actual power will depend on several factors, such as the type of

machine and rotor used the sophistication of blade design, friction losses, and the

losses in the pump or other equipment connected to the wind machine. There are

also physical limits to the amount of power that can be extracted realistically as a

result of losses experienced in power production using windmills a 59.3% of the

power from the wind is likely to be converted into electric power. So, modifying the

formula for ‘Power in the wind’ we can say that the power which is produced by the

wind machine can be given by:

PM = ½.Cp.ρ.A.V3

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Where, PM is power (in watts) available from the machine

cP is the coefficient of performance of the wind machine

Where, PA is the average power output in watts over the year

V is the mean wind-speed in m/s.

The kampala wind graph.

Wind speed increases with height above the ground, because of the earth’s

boundary layer. This effect is modeled using the power law relation

Vz= V10 (z/10) α

Where

VZ =Wind speed at some height z (in meters),

V10= Wind speed at 10 meters (meteorological department weather forecasting

and reporting of wind speeds height),

Α (0.2) and is the power law exponent or index and is most common for wind

turbine analysis.

Our system design will use a four meter diameter windmill to give a 0.7kW thus

chose to have a 1kW windmill due to inverter and converter losses besides when we

have low blowing winds. The graph below depicts the power produced at various

wind-speeds in Kampala ranging from 0m/s to 14m/s measured at 18m the height of

the tower modelled using the wind power law relation.

The x-axis represents wind-speeds in m/s

While the y axis represents the wind turbine power output in watts.

X 0 2 4 6 8 10 12 14

Y 0 0.05 .19 0.3 0.42 0.56 0.74 1.1

Table 2.1: wind speed Vs output power

15

Figure 2.6: A plot of wind output power (Kw) against wind speed (m/s)

The wind turbine torque on the shaft can be calculated by using the following

equation,

Pwb is the extracted power from the wind, _ is the air density (kg/m3), R is the blade

radius (m), Vw is the wind speed (m/s), λ is the blade pitch angle (deg), β is the

rotational speed (rad/s) and Tm is the wind turbine output torque (Nm).

The excitation of a PMSG is provided by permanent magnets instead of field

windings. These permanent magnet machines are characterized as having large air

gaps, which helps to reduce the flux linkage even in machines with multi-magnetic

poles.

16

Figure 2.7: PMSM Operation mode.

From the MATLAB help file, PMSM is able to operate in two different modes –

generator mode and motor mode, as shown in Figure above. The input mechanical

torque will decide the mode of operation is where positive torque indicates motor

mode and negative torque indicates generator mode. The advantages of using PMSG

in a wind system are it has high efficiency and high power density.

Moreover, the absence of gearbox and lack of moving contacts on the PMSG

increase the reliability and lower the maintenance requirement.

2.4 Power Electronic Circuit

Power electronic circuits are used in converting electrical energy. To have a common

source in the hybrid system that combined wind and PV model, power converter is

needed to convert alternating current (AC) to direct current (DC) or vice-versa. The

conversion is perform by solid-state semiconductor devices that operate with

periodically switched on and off at a desired frequency. Therefore, power electronic

converter also known as switching converter because the output is controlled by

switches.

For this project, power converter AC-DC rectifier and DC-AC inverter will be used to

complete the hybrid wind and PV model.

17

2.3.1 AC-DC Rectifier

A rectifier is a power electronic device that converts alternating current (AC) source

to direct current (DC) source using power diodes or by controlling the firing angles

of controllable switches. In this project, a three phase full wave AC- DC rectifier as

shown in Figure below is connected to the output side of the wind model. It will

convert the AC voltages generated by the wind model into DC voltages. The Rectifier

model has been realized using a 3- phase Universal Bridge Simulink block. The

scheme of modeling is- The Universal Bridge block implements a universal three-

phase power converter that consists of up to six power diodes connected in a bridge

configuration.

Figure 2.8: Three phase full wave bridge rectifier.

2.3.2 Inverter

Presently, our main purpose of using the inverters here is to convert the dc power

from both wind and solar system into single-phase ac power. This power is used to

meet the load demands under emergency conditions when there is either a shortage

of generation or that of the wind. Since the voltage level of this ac power is not

constant due to different irradiances and temperature, we have a connected a buck

converter at it’s output to improve the efficiency of the output DC power. The

18

inverter that we have used here is an IGBT-DIODE based inverter connected in the

bridge configuration.

Figure 2.9: Igbt-diode inverter

PWM control of inverter gives variable voltage and variable frequency output.

Average power flow can be bidirectional if the DC source can accept power input.

2.3.3 DC-DC Converter Analysis.

Buck Converter

A buck converter or voltage regulator is also called a step down regulator since the

output voltage is lower than the input voltage. In a simple example of a buck

converter, a diode is connected in parallel with the input voltage source, a capacitor,

and the load, which represents output voltage.

A switch is connected between the input voltage source and the diode and an

inductor is connected between the diode and the capacitor, shown in Figure 2.10

below.

19

Figure 2.10: Basic buck converter.

2.5 Hybrid Wind and Photovoltaic Power System

A standalone PV or wind power system is not able to provide sufficient power to the

load connected due to intermittent energy source. To accommodate every

requirement of energy and providing stabilize output power to the consumers, a

hybrid system with energy storage is purpose. The advantages of using renewable

energy hybrid system are it causes no pollution and these energy sources are widely

available throughout east Africa.

The wind turbine power system connects to AC-DC rectifier to convert the AC output

into DC output. On the other hand, the PV power system is connected to DC-

DC converter to improve the efficiency of the power generated. Both generated DC

output power will be combined at the DC bus at then supply to the loads. Extra

energy will be stored into the energy storage system. The proposed hybrid system is

illustrated in Figure 2.11 below,

20

Figure 2.11: proposed design for the Hybrid power project.

Figure 2.12 depicts our system parameters that we used objectively to design our system

Figure 2.12: proposed design for the Hybrid power project for a simple domestic installation

with a total power output 2kW.

With the above excel sheet showing the total power expected to be connected in a

single day all at once we are able to design the size of the panel. These are the

formal and most used methods in solar panel sizing.

2.6 Conclusion

In order to develop a functional model for hybrid system, the characteristic

equations of each standalone system need to be determined.

Moreover, identifying the parameters that affects the results of the simulation and

the possible types of power converter used helps to develop a comprehensive hybrid

model.

21

CHAPTER 3

METHODOLOGY, DESIGN AND IMPLEMENTATION

3.1 Introduction

This chapter explained the block modeling of photovoltaic power system, wind

turbine power system, hybrid power system, battery system, AC-DC rectifier, DC-AC

inverter, and buck converter. In addition, the MATLAB Simulink circuit block models

for each system were shown in respective section.

3.2 Modeling of Photovoltaic Power System

In this project, an equivalent circuit of a photovoltaic cell is used to produce a DC as

would have been produced by a module or photovoltaic array.

The solar cell is the basic unit of a photovoltaic module and it is the element in

charge of transforming the sun rays or photons directly into electric power. The solar

cell used is the PN junction, whose electrical characteristics differ very little from a

diode, represented by the equation of Shockley (diode equation).

…………………………. (1)

So, the process of modelling this solar cell can be developed based on being the net

current of the cell, the difference of the photocurrent Il or Iph, (the current

generated by the incident light, directly proportional to the sun irradiation) and Id

(the normal diode current),

Characteristics of PV cell

An ideal PV cell is modelled by a current source in parallel with a diode. However no

solar cell is ideal and thereby shunt and series resistances are added to the model as

shown in the PV cell diagram below. RS is the intrinsic series resistance whose value

is very small. RP is the equivalent shunt resistance which has a very high value

22

Figure 3.1: characteristic PV cell

Applying Kirchoff‟s law to the node where Iph, diode, Rp and Rs meet, we get

………………………………. (2)

We get the following equation for the photovoltaic current:

………………………. (3)

Where,

Iph = Insulation current or photocurrent

I = Cell current

I0 = Reverse saturation current

V = Cell voltage

Rs = Series resistance

Rp = Parallel resistance

VT = Thermal voltage

K = Boltzman constant

T = Temperature in Kelvin

q = Charge of an electron

23

………………………. (4)

Therefore, the ideal solar cell can, theoretically, be modelled as a current source in

anti parallel with a diode. Improving the PV cell model includes the effects of series

and shunt resistance.

Simulink block diagram of the PV cell.

Figure 3.2: Simulink model of a photovoltaic solar cell

Modelling of a standalone Photovoltaic system.

Figure 3.3: PV cell standalone connected to the Load through battery storage.

24

3.3 Modeling of Wind Turbine Power System

The wind turbine power system consists of a wind turbine model and a

Permanent Magnet Synchronous Machine (PMSM) block that was already available in

the Simulink library.

The model of wind turbine was developed based on its steady-state characteristics,

as per the wind turbine block in Simulink. Include inside the model was a subsystem

that used to determine the power coefficient Cp (λ, β) value when tip speed ratio

(λ) and blade pitch angle (β) change. Figure 3.4 shows the wind turbine block model

while the Cp (λ, β) block model was shown in Figure 3.5.

The varying wind speed was the input into the wind turbine. Mechanical torque

produced by the wind turbine will then directed to PMSM that converts mechanical

energy from wind turbine into electrical energy.

Tm

The Simulink input of the block is the mechanical torque at the machine's shaft.

When the input is a positive Simulink signal, the asynchronous machine behaves as

a motor. When the input is a negative signal, the synchronous machine behaves as a

generator. The input signal is in p.u. as we have used the p.u. mask here i.e.,

Asynchronous Machine p.u. Units.

M

The Simulink output of the block is a vector containing 21 signals. We have de-

multiplexed these signals by using the Bus Selector block provided in the Simulink

library. Depending on the type of mask we use, the units are in SI, or in p.u. In our

project we have used it in p.u mask.

25

A three phase V-I Measurement block has been placed at the output terminals of

the generator to compute the line voltages and line currents coming out from the

generator, which can also be viewed in the scope. Another measurement block

present in the Simpower System of the Simulink Library by the name of Discrete 3-

phase Power has also been used. This measurement block takes the generator line

voltages and currents as its inputs and enables us in computing the instantaneous

power and mean power produced by the generator at its output.

Figure 3.4: Simulink wind turbine model and its respective parameter.

26

The first input is the generator speed in per unit of the base generator speed i.e.,

we feedback the rotor p.u speed to the wind turbine model. The second input is the

blade pitch angle (beta) in degrees. Power is not equal to the reference power

(which controls the generation). The third input is the wind speed m/s.

The performance coefficient Cp of the turbine is the mechanical output power of the

turbine divided by wind power and a function of wind speed, rotational speed, and

pitch angle (beta).Cp reaches its maximum value at zero beta. The output is the

torque applied to the generator shaft in per unit of the generator rating.

Figure 3.5: Turbine output power Vs Turbine speed

27

Figure 3.6: Wind turbine block model

Figure 3.7: Cp (λ, β) block model

28

Figure 3.8: Wind turbine, 2 mass drive Train and PMSM block model.

The wind system model was simulated by setting the tip speed ratio to 0 and blade

angle as zero [Cp (0, 1)]. This will ensure the system achieves maximum power

coefficient of 0.48, which enable the system to generate maximum power output.

The mechanical torque produce by the wind turbine will be directed into the PMSM,

which has a 8500 RPM reference speed with the purpose of adjusting the generator

speed to enable maximum output generated. The overall wind system model was

illustrated in Figure 3.8 above.

29

3.4 Model of Battery Circuit

PV panels only provide power during the daylight hours and many applications

require energy when the sun is set, hence a battery is often needed to store energy.

A real battery has an internal resistance and is often modeled with an equivalent

circuit consisting of an ideal battery of voltage VB in series with some internal

resistance Ri. During the charge cycle, the applied voltage needs to be greater than

the battery voltage and during discharge cycle; the output voltage is less than VB.

Figure 3.9: Equivalent circuit of battery and I-V characteristic graph.

Battery is an electrochemical device that converts chemical energy into electrical

energy. The most commonly used battery is the lead acid battery because of its low

cost and simple charging process. The cell in a lead acid battery consists of lead

electrodes in an electrolyte of aqueous sulphuric acid. The anode is made up of lead

and cathode is lead oxide. Inside the cell, the oxidation and reduction reaction takes

place for discharging and charging. The regulated output from the boost converter is

fed to the battery circuit for storing energy. Here two lead acid batteries are used in

series for storing the charge. Each battery has the following characteristics shown in

table 3.1. The complete model for testing the battery characteristics is shown in

figure below. The discharge characteristic of the battery is shown in figure 3.10

below.

Parameters of lead acid battery

30

Parameters Values

Nominal Voltage 12V

Rated capacity 200Ah

Initial state of charge(SOC) 50%

Nominal discharge current 86.9565

Table 3.1: parameters of lead acid battery

Model of the battery circuit

Figure 3.10: Simulink model of the battery circuit.

Figure 3.11: Battery discharge characteristics.

31

3.5 Modeling of AC-DC Rectifier

The hybrid system with battery storage will at some point be operated in DC voltage.

Therefore rectifier is needed to convert the AC voltage generated by the wind power

system into DC voltage. Figure shows the rectifier model, where it was developed

using a universal bridge block that have Thyristors as the power electronic switch.

The Rectifier model has been realized using a 3- phase Universal Bridge Simulink

block. The scheme of modeling is- The Universal Bridge block implements a

universal three-phase power converter that consists of up to six power switches

connected in a bridge configuration. Diodes have been chosen as the power

switches and a 3 arm converter configuration is adopted using the universal bridge

block properties.

32

Figure 3.12: Rectifier block and parameters

3.6 Inverter model

To implement the bridge inverter, we have used the IGBT-diodes model present in

the Simpower Systems of the Simulink Library in Matlab 7.9.0, connected in a bridge

configuration, implemented as a single phase inverter.

Figure 3.13: Inverter Model

One of the most promising means of controlling the inverter output voltage is to

incorporate time ratio control within the inverter using a suitable modulation scheme

i.e., by suitably controlling the ON-OFF time of the switches we control the output

voltage. These inverters are called Pulse width modulated inverters.

3.7 spwm technique

The gate pulse requirement of the inverter bridge is taken care of using a PWM

Generator.

33

Figure 3.14: PWM Generator Parameters

Buck converter model in Simulink

Figure 3.15: Buck converter model in Simulink

34

Standalone Wind power system connected to load.

Figure 3.15: Standalone Wind power system connected to load

3.8 Modeling of Hybrid System with battery storage.

After having completed the standalone system modeling for PV model, wind model

and battery storage model, all individual model were connected as hybrid system.

Hybrid system was formed with wind model and PV model. AC voltage generated by

wind model was rectified and converted into DC voltage. It was added with DC

voltage from PV model which was also inverted into AC and then connected to the

load. On the other hand, the battery storage model was connected in parallel with

the hybrid system. The hybrid system model is shown in Figure 3.16.

35

Figure 3.17: Stand-Alone Hybrid Project

The hybrid input and output voltage, battery state of charge, current output are the

focus during simulation. All of these output parameters are measured using a scope.

Conclusion

The block modeling for the wind and PV hybrid system, the battery storage system

and also the AC-DC rectifier were shown in this chapter. The photovoltaic model was

developed based on its characteristic equations, Besides that, a wind turbine model

was developed based on its steady-state characteristic equations .Then the wind

turbine model was added with a PMSM block to form the complete wind model. The

battery storage system was modeled with Simulink blocks of the lithium battery.

Moreover, the rectifier model was developed using a universal bridge block that have

diodes as the power electronic bridge. Lastly, all individual models were connected

as hybrid system.

36

CHAPTER 4

SIMULATION RESULTS AND DISCUSSIONS

4.1 Introduction

The models shown in the above figures were simulated using MATLAB® /

SIMULINK®

This chapter displays the input parameters and also the simulation results obtained

from MATLAB Simulink. The input wind speed variations, the changing PV irradiation

level, the characteristic of PV and wind model, the results from standalone system

simulation and the results from hybrid system at different wind speeds and solar

irradiances were plotted in graph and all the relevant data were recorded in table.

Analysis and discussion were done to determine the hybrid system output voltage

stability at constant parameters.

4.2 Photovoltaic Model Simulation

During the photovoltaic model simulation, the temperature parameter was set at

constant value 27.5°C and the irradiance parameter was set at 400 W/m2, 600 W/m2

and 1000 W/m2 respectively. The output voltage waveforms at different irradiance

value were shown in Figure 4.1 (a), (b), (c).

37

Figure 4.1 (a) at 400W/m2

Figure 4.1 (b) at 600W/m2

38

Figure 4.1 (c) at 1000W/m2

Fig PV model output voltages at (a) 400W/m2 (b) 600W/m2 (c) 1000W/m2

From Figure 4.5, a voltage output of 160.4V was obtained at 400 W/m2 irradiance,

160.6V at 600 W/m2 irradiance and 161V at 1000 W/m2 irradiance while maintaining

the PV model temperature at 27.5°C. The results indicates that the higher the

irradiation level, the greater output voltage can be generated by a PV model.

39

Figure 4.2: P-V characteristics

Figure 4.3: P-I characteristics

The IV and PV curves for various irradiance but a fixed temperature (250C) are

shown above in figures. The characteristic I-V curve tells that there are two regions

in the curve: one is the current source region and another is the voltage source

region. In the voltage source region (in the right side of the curve), the internal

impedance is low and in the current source region (in the left side of the curve), the

impedance is high. Irradiance temperature plays an important role in predicting the

40

I-V characteristic, and effects of both factors have to be considered while designing

the PV system. Whereas the irradiance affects the output, temperature mainly

affects the terminal voltage. From the PV characteristics we can observe that, there

is a point at which the power output is maximum for a given condition of irradiance

and load. If we are operating the PV panel at this point, operation of PV panel at this

region gives the maximum efficiency.

4.3 Wind model simulation

The input wind speed into the wind model was randomly varied between 4 m/s and

10 m/s, which are the typical wind speed available in Kampala.

The graph below, Figure 4.4 depicts the output voltage and currents of this system

Figure 4.4: voltage and Current out-puts of a wind generator respectively

41

From Figure 4.5, a maximum wind generator output voltage of 250V and 10Amps AC

three phase voltage was observed. The wind system output then went through an

AC/DC rectifier, which converted the AC voltage into DC voltage. After that, a

constant output voltage of 250V DC was generated, then fed to the DC link.

Figure 4.5: Buck Converter Voltage and Current Output

The below figures show the output of a solar PV cell and wind generator voltage at

the load respectively; it’s observed that unlike hybrid systems standalone systems

produce less voltage which may only sustain the load for a few hours but,

adequately whereas with hybrid, there is a constant power supply since when power

source is not functional, the other is and when both systems are functional a desired

output is realized and more loads can be added onto it.

42

Figure 4.6 (a): PV output at the Load

43

Figure 4.6 (b): Wind Turbine output at the Load

Figure 4.7: output voltage waveform of the hybrid system.

44

CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

The objectives of this project are to develop and simulate a hybrid system that

combines the wind model and the PV model. Then develop an energy storage

system (battery) and simulate together with the hybrid system. The overall hybrid

system will be tested with varying irradiation level for the PV model and changing

wind speed for the wind model to show the variations of these inputs with the

output power inside a hybrid system.

Simulation results show that hybrid system has greater reliability compared to

standalone system because it is based on more than one type of electric generation

source. When either one of the generation system does not operate at its full

capacity due to inconsistent energy source, another system will operate and

compensate the extra load demand. In addition, the hybrid system also able to

produce a greater output voltage compare to standalone system.

5.2 Recommendations

In addition, the design and simulation of hybrid system and energy storage system

can be performed using different type of software such as PSCAD or use a newer

version of MATLAB simulation software. Although MATLAB 7.9 (R2009a) version is

still applicable in this project, but the latest version of MATLAB 7.14 (R2012a) would

provide a comprehensive list of blocks for the hybrid system and energy storage

modeling in Simulink.

45

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48

Appendix I

Solar module:

49

Appendix II

MATLAB CODE FOR PV ARRAY.

T=302; Tr1=40; Tr=298; S=[100 80 60 40 20]; %S=70; Ki=0.00023; Iscr=3.75; Irr=0.000021; K=1.38065*10^(-23); q=1.6022*10^(-19); A=2.15; Eg0=1.166; alpha=0.473; beta=636; Eg=Eg0-(alpha*T*T)/(T+beta)*q; Np=4; Ns=60; V0=[0:1:300]; for i=1:5 Iph=(Iscr+Ki*(T-Tr))*((S(i))/100); Irs=Irr*((T/Tr)^3)*exp(q*Eg/(K*A)*((1/Tr)-(1/T))); I0=Np*Iph-Np*Irs*(exp(q/(K*T*A)*V0./Ns)-1); P0=V0.*I0; figure(1) plot(V0,10); axis([0 50 0 20]); xlabel('Voltage in volt'); ylabel('Current in amp'); hold on; figure(2) plot(V0,P0); axis([0 50 0 400]); xlabel('Voltage in volt'); ylabel('Power in watt'); hold on; figure(3) plot(I0,P0); axis([0 20 0 400]); xlabel('Current in amp'); ylabel('Power in watt'); hold on; end