MODELING AND SIMULATION OF INVERTER-

CONTROLLED HYBRID PHOTOVOLTAIC-WIND

CONNECTED TO THE GRID GENERATION

SYSTEM

DAHIR KHEYRE DIBLAWE

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

i

MODELING AND SIMULATION OF INVERTER-CONTROLLED HYBRID

PHOTOVOLTAIC-WIND CONNECTED TO THE GRID GENERATION

SYSTEM

DAHIR KHEYRE DIBLAWE

A project report submitted in

fulfillment of the requirement for the award of the

Degree of Master of Electrical Engineering

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

JANUARY, 2018

iii

My dedication goes to:

For my beloved Mother and Father

Whose hearts are always with me and their prayers light on my daily live.

Thanks for everything, I cannot thank enough for your patience and unlimited

support on my side.

I also want to thank brothers, sisters, uncles, aunts, friends, relatives and all those

who have been a great help in the completion of this thesis project directly or

indirectly.

iv

ACKNOWLEDGMENT

First and foremost I want to thank Allah for his guidance and protection throughout

my life. I would like also to express my gratitude to Universiti Tun Hussein Onn

Malaysia (UTHM) and Faculty of Electrical and Electronic Engineering Department

of Electrical Power Engineering for giving me the opportunity to gain experience and

valuable knowledge. Most of all, the excellent facilities, adequate tool and equipment

in laboratory are truly appreciated.

I am also deeply delighted my supervisor, Dr Asmarashid Bin Ponniran for

giving me his assistance, guidance and encouragement to carry out my project.

Without his guidance and knowledge, I would not be able to finish this project thesis.

He has given his best in order to make sure that I am under his supervision and

understand the concept of the project.

Finally, I would like to thank all my course-mates and friends who had understand

my problems throughout this project been carried out, and keep encouraging me,

contribute relevant ideas for my project and help me research, their helps, advices and

encouraging words are deeply appreciated, truly from the bottom of my heart.

.

v

ABSTRACT

The rapid growth demand for energy and the depletion of fossil fuels leads researchers

to develop alternative and sustainable energies sources like wind and solar renewable

sources which is becoming the largest potential in renewable energies. The aim of this

project is to design 10kW hybrid PV-Wind hybrid connected to the grid generation

system, this system is regulated by the common DC link in order to contribute some

power to the grid. The project consists of Permanent Magnet Synchronous (PMSG) as

a wind generator, solar connected in series and parallel modules, DC-DC Boost

converter equipped with MPPT, this, Maximum power point tracker (MPPT) control

is essential to extract the maximum power of the output of photovoltaic power

generation system and wind turbine at its maximum power point. Perturbation &

observation (P&O) strategy is utilized and modelled in MATLAB/Simulink. This

strategy is modest in operation and hardware requirement is minimal, a Phase Locked

Loop (PLL) is used for control of multifunctional VSC. The voltage source converter

(VSC) controller uses the load and source forward terms for fast dynamic response by

regulating and giving required power to the grid. The simulation studies are performed

on MATLAB/Simulink. The alternating power from the sources is connected voltage

source inverter which regulates the injected DC voltages before sending to the grid.

This inverter transfers the energy drawn from the wind turbine and PV array to the

grid by keeping common DC voltage in constant value. The simulation results

demonstrates the control performance and dynamic behaviour of the hybrid PV-wind

connected to the grid generation system by using MATLAB/Simulink.

vi

ABSTRAK

Keperluan tenaga yang meningkat secara mendadak dan bahan api fosil yang semakin

berkurangan mendorong penyelidik untuk mencari sumber tenaga alternatif seperti

tenaga solar dan angin. Tenaga ini berupaya menjadi tenaga yang boleh diperbaharui.

Tujuan projek ini adalah untuk mereka bentuk hibrid 10kW hibrid PV-Angin yang

disambungkan ke sistem penjana grid. Sistem ini dikawal oleh pautan voltan arus terus

untuk menyumbang tenaga ke dalam grid. Projek ini menggunakan magnet kekal

segerak (PMSG) sebagai penjana angin, panel solar yang disambungkan secara siri

dan selari, penukar DC-DC Rangsangan dan grid suai muka songsang. Strategi

kawalan kuasa digunakan untuk menghasilkan kuasa maksimum. Kawalan penjejak

titik kuasa maksimum (MPPT) adalah penting supaya keluaran bagi system penjana

kuasa fotovoltaik dan turbine angin adalah maksimum. Kaedah gangguan dan

pemerhatian (P&O) digunakan dan disimulasikan dalam MATLAB/Simulink. Kaedah

P&O beroperasi dengan mudah dan keperluan perkakasan adalah rendah. Gelung

Terkunci Fasa (PLL) digunakan untuk mengawal VSC yang mempunyai pelbagai

fungsi. Pengawal penukar sumber voltan (VSC) menggunakan beban dan sumber ke

hadapan untuk tindak balas dinamik yang cepat dengan mengawal selia dan memberi

kuasa yang diperlukan kepada grid. Kajian simulasi dilaksanakan dalam

MATLAB/Simulink. Kuasa ulang alik dari sumber disambungkan kepada sumber

voltan songsang untuk mengawal selia voltan terus yang dimasukkan sebelum dihantar

ke dalam grid. Suai muka sumber voltan songsang dengan grid memindahkan tenaga

dari turbin angin dan susunan PV ke dalam grid dengan mengekalkan nilai voltan terus.

Hasil daripada simulasi menunjukkan prestasi kawalan dan sifat dinamik hibrid PV-

Angin yang disambungkan ke system penjana grid dengan menggunakan

MATLAB/Simulink.

vii

TABLES OF CONTENTS

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGMENT iv

ABSTRACT v

ABSTRAK vi

TABLES OF CONTENTS vii

LIST OF FIGURES x

LIST OF TABLES xii

CHAPTER 1 INTRODUCTION 1

1.1 Overview 1

1.2 Problem Statement 3

1.3 Objectives 4

1.4 Scope of the project 4

1.5 Research Motivation 5

1.6 Thesis outline 5

CHAPTER 2 LITERATURE REVIEW 6

2.1 Background of the Project 6

2.2 Modeling of Photovoltaic (PV) Module 7

2.2.1 Modeling PV cell 7

2.3 Photovoltaic Modeling 8

viii

2.4 Photovoltaic Array Characteristics 10

2.5 Effect of Irradiance and Temperature 11

2.6 DC-DC Boost Converter 13

2.6.1 Modes of Operation 14

2.6.3 Mathematical equation of Boost Converter 14

2.7 Maximum Power Point Tracking (MPPT) 16

2.7.1 Perturb and Observe (P&O) Method 17

2.8 Wind Energy 19

2.9 Wind Turbine characteristics 20

2.10 Permanent Magnet Generator 21

2.11 Diode Rectifier with MPPT Controlled Boost Converter 21

2.12 Summery of literature review 22

CHAPTER 3 METHODOLOGY 24

3.1 Introduction 24

3.2 Flowchart of Proposed Hybrid System 25

3.3 Proposed Control strategy 27

3.4 Modeling Voltage Source Inverter (VSI) 28

3.4.1 Phase Locked Loop 29

3.4.2 abc to dq0 Transformation 30

3.4.3 Pulse Width Modulation 31

3.4.4 DC Voltage Controller 32

3.4.5 PI Current Controller 33

3.5 Grid Filters 33

CHAPTER 4 RESULTS AND DISCUESSION 35

4.1 Introduction 35

4.2 Parameter Specification 36

4.2.1 PV and Wind sources Specification 36

4.2.2 Boost Converter Specification 39

ix

4.2.3 Inverter and Grid side Specification 42

4.3 Discussion 44

CHAPTER 5 CONCULUSION 46

5.1 Conclusion 46

5.2 Future Prospects 47

REFERENCES 48

APPENDICES 52

x

LIST OF FIGURES

1.1 Grid-connected Hybrid PV-wind block diagram 2

2.1 Ideal Single Diode Circuit 7

2.2 Characteristic I-V curve of the PV cell 8

2.3 Photovoltaic Module Circuit 8

2.4 Sample I-V Curve [17] 10

2.5 Different Irradiation Curves in PV Modules 11

2.6 Different Temperature I-V Curves in PV modules 11

2.7 Partial Shading Effect 12

2.8 Boost Converter Circuit [2] 13

2.9 Mode 1 and 2 Operation 14

2.10 Boost Converter Inductor Current Waveform [18] 15

2.11 MPPT in Photovoltaic Source 16

2.12 Flowchart of P&O MPPT Technique 17

2.13 Wind Turbine Characteristics [22] 21

3.1 Flowchart of Hybrid PV-Wind Generation 25

3.2 Control Strategy for Grid Connected Hybrid system 27

3.3 Block Diagram of the Inverter Controller 28

3.4 Transformation of abc to dq0 in aligned a and q axis [1] 30

3.5 Transformation of abc to dq0 in aligned a and d axis [1] 30

3.6 DC link Voltage Controller 32

3.7 LC filters 34

4.1 I-V and P-V curve for SPR-305-WHT Solar 37

4.2 Three phase AC Output line voltage of the PMSG 38

4.3 Wind Turbine Output Voltage 38

4.4 Wind Turbine Output Power 39

4.5 Input Voltage of the PV Source 40

xi

4.6 Input Voltage of the Wind Source 40

4.7 Duty cycle Adjustment for the PV side 41

4.8 Duty cycle Adjustment for Wind side 41

4.9 Common DC link Voltage and its Modulation index 42

4.10 PV and Wind Generated Power 43

4.11 Hybrid Generated Power 43

4.12 Grid Voltage and Current 44

xii

LIST OF TABLES

1 PV array Specification 36

2 Wind Generator Specification 37

3 5 kHz Boost Converter 39

4 Inverter and grid Specification 42

1

CHAPTER 1

INTRODUCTION

1.1 Overview

Due to the critical condition of fossil fuels which include oil, gas and natural gases,

the development of renewable energy sources is continuously improving. This is the

reason why renewable energy sources have become more paramount these days. Few

other reasons include advantages like abundant availability in nature, eco-friendly

and recyclable [3, 4]. Many renewable energy sources like solar, wind, hydro and

tidal are there, among these renewable sources solar and wind energy are the world’s

fastest growing energy resources with no emission of pollutants, energy conversion

is done through wind and photovoltaic cells.

The term hybrid is referred as the combination of two or more renewable

sources to cover up optimally in required demand of power. The merging of PV-wind

generates combination of power for complementation of each other by considering

availability of sources. The individual harnessing of wind and solar sources have

uncertain characteristics. For instance, in the day time solar energy is shining, hence

because of the sun density and unforeseeable shading by the trees, or weather

changes, the solar radiation intensity also changes. For this cause solar energy can be

undependable [5]. In the meantime wind can be formed by uneven heating of the

atmosphere and this varies by weather condition. Because of this concept, wind can

be unreliable too.

2

As the individual renewable energy utilization becomes unreliable so it is imperative

to implement hybrid generation system which is more efficient than individual

generation. [6]. In this project, modelling of inverter-controlled hybrid PV-wind

generation system connected to a grid is proposed and simulated. Figure 1.1 shows

proposed complete system block diagram.

MPPT

DC-DCCONVERTER

UNIVERSAL BRIDGE

(RECTIFIER)

DC-DCCONVERTER

MPPT

INVERTER

+

-TRANSFORMER

GRID

PV SOURCE

WIND SOURCE

+

-

C

Figure 1.1: Grid-connected Hybrid PV-wind block diagram

The suggested hybrid system contains two separate sources which is PV and wind

source, in the proposed system, contains wind turbine and PV as sources, the wind

turbine has PMSG which is built-in generator to produce AC power from moving rotor

of the wind. In the other side, there is PV sources which produces DC voltage which

is then boosted to the desired voltage by the DC-DC boost converter. This two sources

shares common DC link voltage which is injected to the inverter this inverter harnesses

DC power from the PV array and the wind turbine which maintains the voltage and

frequency of the grid [7].

3

1.2 Problem Statement

Wind and solar energy are reliable energy sources. However, the renewable energy

generation has drawbacks that the change of the output characteristic becomes intense

because the output greatly depends on climatic conditions, including solar irradiance,

wind speed, temperature, and etc.

Thus, in order to conquer this obstacle is better to hybrid the system, however

to combine renewable energy systems is also big challenge because of the different

characteristics of the different sources and it is response of fluctuating load, the main

confrontation of the hybrid is synchronization of the system from the source to the

load, so it is required to keep constant DC output voltage for both sources whether the

both sources is balanced or not.

Many researchers studied and published papers related to the hybrid system.

mostly they used stand-alone systems which is always have constant load, however

when connected to grid suffers a lot of synchronization problems specially in the DC

side, the researchers mostly implemented balanced system which gives almost

constant DC output voltage by using battery bank to compensate the DC voltage

required by the inverter, thus this is not suitable for the unbalanced sources and also

not cost-effective as they need to have always battery bank.

Thus, in this project is proposed “modelling of inverter-controlled hybrid PV-

wind connected to a grid generation system”. in this work focuses on controlling DC

link voltage which is to be injected to inverter, the proposed inverter control compares

the voltages comes from the two sources and referenced voltage before processing to

the grid, if the referenced voltage is higher than the input voltages from the sources,

boost converter having maximum point tracker (MPPT) is equipped in order to boost

inputs voltages to referenced voltage by varying the duty-cycle. The proposed control

criteria operates well and keeps unity power factor ,but mostly suffers to high power

PV-wind sources, as the inverter losses synchronization and could not afford to keep

unity power factor and compensate the DC voltage from the sources.

4

1.3 Objectives

Objective of this project is as follows:

(i) To model hybrid photovoltaic-wind connected to the grid generation system

having DC boost converter equipped with MPPT controller

(ii) To examine dynamic performance of the MPPT for implementation of the

hybrid system.

(iii) To control and keep constant in common DC-link voltage for the hybrid system

connected to the grid.

1.4 Scope of the project

The project scope is as follows

(i) The system is based on grid connected hybrid PV-wind generation system for

remote areas power supply.

(ii) Modelling solar and wind combination equipping with boost converter is used

by simulating MATLAB \Simulink.

(iii) Sun Power SPR-305E-WHT-D solar type is validated for solar modelling, and

permanent magnet asynchronous generator (PMSG) wind type also used for

wind turbine modelling.

(iv) Perturb and Observe (P&O) maximum power point tracker (MPPT) strategy is

used for the DC boost converter.

(v) 3-Φ voltage source inverter (VSI) is implemented as the control criteria for DC

–link voltage.

5

1.5 Research Motivation

Nowadays renewable energy sectors are getting more attention towards developed

countries due to affordability and cheaper. For instance, according to the [8], the

investment in renewable energy was higher in the world’s poorest countries than the

richest ones for the first time last year, to a major new report. A total of about £196.5

was spent renewable power and fuels globally in what was a record year for investment

in the sector.

1.6 Thesis outline

This report contains five chapters. Chapter 1 explains introduction of the project. It

also determines the background of the project. This also summarizes and reviews all

the main structure of the project. It includes problem statement, objectives of the

project, motivations and its scope.

Chapter 2 basically reviews and discusses previous research and finding for

this area and how it relates to this work. This also determines some refinement from

previous work to merge the goal of the project.

In chapter 3 discussed methodology of the project, the design and methods used

are explained in this chapter as well as developing the hybrid controlled system in

MATLAB\Simulink.

Chapter 4 states in detail all the results approved in the system by showing and

proving the functioning of all the components of the system and lastly gives the

discussion of the all results in the project.

Lastly, chapter 5 concludes and summarizes the project by pointing out some

of the future work expansion and recommendation for the project.

6

CHAPTER 2

LITERATURE REVIEW

2.1 Background of the Project

Solar power is energy from the sun that is converted into thermal or electrical energy.

Solar energy is the cleanest and most abundant renewable energy source available,

Modern technology can harness this energy for a variety of uses, including generating

electricity, providing light or a comfortable interior environment, and heating water

for domestic, commercial, or industrial use.

The sun radiates 174 trillion kWh of energy to the earth per hour, In other

words, the earth receives 1.74 x 10 17 watts of power from the sun [9].The estimated

distance from the sun is 150,000,000 km while the sun is stationed and spins around

by the earth in an elliptic orbit, the light having the travelling speed of 300,000 km/sec

to overcome the aforesaid distance, it consumed approximately 8.5 minutes [10].Wind

turbine theory has progressed rapidly in recent years and it was at the hub of high tech

industry. This is becoming more powerful, with the latest turbine models having larger

blade sizes which can generate more wind which in return produce more electricity

[11]. Solar-wind hybrid generation system is the combination of power generating by

solar photovoltaic modules and wind turbines. Using this system, power generation by

the turbines when there is enough wind the wind and generation from the PV module

when there is sunlight radiation is available can be achieved. Both systems can

generate power when both sources are available [12].

7

2.2 Modeling of Photovoltaic (PV) Module

The modeling of the photovoltaic modules can be designed by connecting series and

parallel combination in photovoltaic cells to acquire high power.

2.2.1 Modeling PV cell

The photovoltaic cells is made of combination photonic current from the cell with

diode for directing the generated current from the cell. Figure 2.1 shows basic circuit

of ideal PV cell.

Sunlight

phI DI

cellI

cellV

+

-

Figure 2.1: Ideal Single Diode Circuit

The general Equation from the characteristics of semiconductors that describes the I-

V characteristic of ideal PV cell is [13].

Where pvI is the light photons current,DI is the diode equation, ,o cellI is the reverse

leakage current of the diode, and q is the electron charge.

, exp 1

d

pv ph o cell

I

qVI I I

akT

(2.1)

8

As shown in Figure 2.2, the I-V curve comes in Equation (2.1). The net cell current I

contains of the light-generated current pvI and the diode current DI .

Figure 2.2: Characteristic I-V curve of the PV cell

2.3 Photovoltaic Modeling

In general, the Equation (2.1) of the basic photovoltaic cell does not determine the I-

V characteristic of a modern PV array. Modern arrays are made of string connected

PV modules, and analyzing of the characteristics of PV arrays need to implement PV

module. The implementation of the PV module is created from the equivalent circuit

of PV module as shown in Figure 2.3, this circuit based on single diode PV module.

Sunlight

phI DI shR

sR

Load

+

-

pvI

Figure 2.3: Photovoltaic Module Circuit

9

From the Figure 2.3 in photovoltaic module circuit can be simplified by using

Kirchhoff’s Current Law (KCL), diode characteristic, and Kirchhoff’s Voltage Law is

formed [14]:

In KCL for the diode characteristic

For KVL:

In Equation (2.3), diode characteristic is shown by diode current DI ,while in KVL

shows the Equation (2.4) for ,pv cellV .The general observation characteristic in PV

array current can be [15]:

Where pvI is the photovoltaic (PV) current and oI is the saturation current, while

/st NV kT q is the thermal voltage of the array with sN cells connected in series module.

When the cells connected in series, it increases the generated output voltages, while

the cells connected in parallel increases the generated current. If the array contains

number of parallel connections of the cells and saturation currents may be expressed

as ,pv pv cell pI I N , ,o o cell PI I N .

0Dph D pv

VI I I

D (2.2)

1D

T

V

V

D OI I e

(2.3)

,pv cell D s pvV V R I

(2.4)

exp 1s pv s pv

pv ph o

t p

V R I V R II I I

V a R

(2.5)

10

The relationship between sR and pR , can be found [16]:

The initial conditions for both sR and pR , can be expressed

In Equation (2.7) determines that for any given value of sR there is identical of pR

that gives the I-V curve.

2.4 Photovoltaic Array Characteristics

The photovoltaic I-V and P-V characteristic is not constant and changes with

irradiation and temperature. At the maximum power point (MPP), the modules gives

the most power available under conditions of irradiance and temperature. Figure 2.4

shows I-V curve of PV module with labelling maximum power point (MPP).

Figure 2.4: Sample I-V Curve [17]

max,

mp m smp V I R

p

mp pv E

VR

V I Id P

(2.6)

0SR ; I

mp oc mp

po

sc mp mp

V V IR

I I

(2.7)

11

2.5 Effect of Irradiance and Temperature

When the irradiance of the solar panels decreases, the power generated will be very

small in a cloudy sky, and it will not effect to the efficiency of solar panels, but it will

minimize production of current because of low current. In Figure 2.5 shows variation

of different irradiation on PV module which produces different maximum output

power.

Figure 2.5: Different Irradiation Curves in PV Modules

In other hand when the surrounding temperature of the PV module increases, the

current produced remains practically unchanged, whereas the voltage decreases which

causes reduction in the performances of the PV panels in terms of produced power. It

is always good to keep under control the service temperature trying to give solar

modules enough ventilation to minimize temperature variation on them. Figure 2.6

shows the effect of variation surrounding temperature in some type of PV modules.

Figure 2.6: Different Temperature I-V Curves in PV modules

12

Furthermore, there is another condition with may experience the use solar panels

which can affect the performance of modules and is called shading condition. When

analyzing this condition can be seen multiple peaks on I-V and P-V curves which

produces different curves in compared to normal condition. In Figure 2.7 shows I-V

and P-V curves under partial condition, the curve determines the optimum output

power on the curve which represents as global maximum power point, while other

power represents as local maximum point.

Local maximum point

Global maximum point

Figure 2.7: Partial Shading Effect

13

2.6 DC-DC Boost Converter

Boost converter is DC-DC power converter whose function is transform the input DC

voltage to the desired and higher. It is function is like a transformer circuit , unlike

transformer changes AC source while the DC-DC converter deals with DC sources ,

the input voltages is stepped up by switching and controlling duty cycle.

The main working principle of boost converter is that the inductor in the input

circuit resists sudden variations in input current. When switch is OFF the inductor

stores energy in the form of magnetic energy and discharges it when switch is closed.

The capacitor in the output circuit is assumed large enough that the time constant of

RC circuit in the output stage is high. The large time constant compared to switching

period ensures a constant output voltage. In Figure 2.8 determines the circuit operation

of DC-DC boost converter.

LoadVs Switch

L D

C

Figure 2.8: Boost Converter Circuit [2]

14

2.6.1 Modes of Operation

In general, the circuit operation of the DC-DC boost converter can be classified in two

operation, this operation depends up on the rate of frequency switching and short

circuit characteristic. For instance when the switch is connected, the inductor L will

likely to be charged, this is considered as the first operation and is called as charging

condition. Hence in the second operation, when the switch is opened, the inductor L

starts discharging by the discharging mode operation. The operation modes is showed

in Figure 2.9.

Load

Vs

L D

C

Vs

L

CS Load

Mode 1 circuitMode 2 circuit

Figure 2.9: Mode 1 and 2 Operation

2.6.3 Mathematical equation of Boost Converter

Figure 2.10 shows the function of inductor current LI that drives the boost converter

and slope determines changes in current of an inductor. In circuit Figure 2.8 ,when the

switch is closed, inductor current increases from 1I to 2I , when switch is ON, the

source voltage is applied to inductor, L INV V .When the switch is OFF, the inductor

current discharges as it cannot comes down instantaneously. Figure 2.10 determines

range of currents in boost converter.

15

Figure 2.10: Boost Converter Inductor Current Waveform [18]

As shown in the waveform, the input current flows through the diode for Toff time as

it tends fall from 2I to 1I when L is reversed. This results the load voltage is boosted

and overrides the input voltage which is formulated by io in

t

dV V L

d . In a boost

converter, the relation between input and output voltage can be expressed:

By the Equation 1 shows that duty cycle. 1 s

o

VD

V , Ripple current,

sil

V D

Lf and

ripple voltage oic

I D

CF .

The voltage and current ripples can be assumed 20 % and 40 % Respectively.Thus, the

design inductor and capacitor can be calculated respectively:

1

ino

VV

D

(2.8)

s

il

V DL

f

(2.9)

o

vc

I DC

f

(2.10)

16

2.7 Maximum Power Point Tracking (MPPT)

Maximum Power Point Tracking (MPPT) is a way to track and get maximum power

point from the hybrid systems, to track maximum power from hybrid systems, it can

be implemented many strategies and each method uses different algorithm which focus

some parameters that to be controlled, the most parameters that to be controlled in

order to get optimum from hybrid systems are voltage, current, speed and etc., for

instance , Solar PV modules can be extracted maximum power by sensing input

voltage and current which later to be switched the adequate duty-cycle pulses, this

algorithm is used with combination of mechanical systems to track solar panel

optimum power based on the changes of irradiance, temperature, in the PV the voltage

that generate maximum power is referred to peak power voltages, the maximum

voltage and maximum current can form maximum power, the MPPT is built-in DC-

DC converters which operates to change input voltages from one stage to another level.

[19]. Figure 2.11 describes PV sources connected to the load.

MPPT

Figure 2.11: MPPT in Photovoltaic Source

17

2.7.1 Perturb and Observe (P&O) Method

The most commonly used MPPT is perturb and observe (P&O) method, this method

has simple algorithm in compared to other MPPT methods, the measured voltage and

current can be sensed, the voltage given as perturbation with its related power

compared to the reference [20]. The loop stops when the maximum output power is

tracked. Figure 2.12 determines the flowchart of the process.

Figure 2.12: Flowchart of P&O MPPT Technique

Measure V(t), I(t)

Start

P(t)=V(t) x I(t)

=P(t)-P(t-1)

V(t)-v(t-1)>0V(t)-v(t-1)>0

Decrease volatge

Increase volatge

Increase volatge

Decrease volatge

Stop

P

0P

YESNO

NO

YES

18

The Perturb & Observe (P&O) maximum power point tracking algorithm is shown in

Figure 2.12, in each temperature and irradiance condition, there is maximum power

point to be tracked and delivered to the load. The P&O technique algorithm calculates

the power P(t) by measuring the instant voltage V(t) and current I(t) and then compares

it with last calculated power P(t-1). The algorithm continuously perturbs the system if

the operating point variation is positive; otherwise the direction of perturbation is

changed if the operating point variation is positive. The duty cycle of the DC-DC

converter is varied till it reaches the maximum power point.in higher perturbation, the

method may oscillate around maximum power point which results loss of energy.

Flowchart of P&O control algorithm is presented as shown in Figure 2.12, this MPPT

is tested using MATLAB\Simulink. The input voltage and current from PV are used

to identify the power Po, which is then compared the present value of power with

previous value. If the value of power is positive then the voltage is increased by

predefined step size. The voltage value of the PV and varied voltage is compared and

steady state error obtained is eliminated by PI controller. To avoid over saturation, a

limiter should be placed at the output which is matched carrier wave to produce pulse

for controlled switch IGBT of the converter.

19

2.8 Wind Energy

Wind turbine is one of the growing renewable energy sectors in the recent years,. Wind

can be generated power using a wind turbine equipped with electric generator. In wind

energy generation using of permanent magnet generator is much preferred in

compared to other, because of having on its self-excitation role, which helps an

operation at a high power with efficiency, the application of the PMSG gives more

attention to recent development of its materials and performances .

Wind can be explained is the motion of air mass which has kinetic energy. This

energy can be transformed into mechanical energy with the uses of wind turbine

having rotor blades. Then through using a generator the mechanical energy is

converted to electrical energy [21].The kinetic energy produced by a moving object is

expressed as

In this case, m is the mass of air and v is the wind velocity. The mass m could be

derived from

Where ρ is the air density

A is the swept area of the rotor blade

d is the distance travelled by the wind.

The mechanical power of the wind turbine (wP ) is defined is the kinetic energy over

the time (t), thus wP is expressed as

The power expressed by Equation (2.13) is the ideal power captured by the wind

turbine. The actual power of the wind turbine depends on the efficiency of the turbine

21

2kinE mv (2.11)

( )m Ad (2.12)

31

2

kinw

WP Av

t (2.13)

20

represented by (λ, β) Cap which is the function of the tip speed ratio (λ) and pitch angle

(β).

The tip speed ratio (λ) is the ratio between the turbine speed and the wind speed, and

is

Where ω is the turbine angular speed, and R is the radius of the turbine. Therefore, the

actual power captured by the wind turbine is given by

Then, the torque of the wind turbine could be expressed as [26]

Where Ct (λ, β) = Cp (λ, β)/ λ is the torque coefficient of the wind turbine. The turbine

power coefficient) Cp (λ, β is a nonlinear function and expressed by a generic function.

The relationship between Torque and power is:

2.9 Wind Turbine characteristics

The wind turbine generates power with different condition of time, the output power

varies with variation of steady wind speed, as shown in Figure 2.13, at low wind

speeds, there is no enough torque applied by the wind blades to rotate, as the wind

rises, the wind turbine blades starts to rotate and generate power, this first speed

rotation is called cut-in speed. When the wind increases, the amount of power

generated increase until it reaches the rated output wind speed which is designed to

wR

v (2.14)

31( , )

2pP C Av (2.15)

21( , )

2tT C ARv (2.16)

mm

PT

(2.17)

21

keep power at constant level. Figure 2.13 determines the characteristics of power with

the variation of wind speed.

Figure 2.13: Wind Turbine Characteristics [22]

2.10 Permanent Magnet Generator

Permanent magnet excitation is generally popular in newer smaller scale turbine types,

since it enables higher efficiency in addition to smaller wind generator blade [23]. The

advantage of permanent magnet synchronise generators (PMSG) over the other

generators is that it does not necessitate any external excitation current. The other

benefits by the cos aspect is, it can be used diode bridge as the generator device which

also does not require external excitation, this type of generator has been common in

recent applications.

2.11 Diode Rectifier with MPPT Controlled Boost Converter

As the wind speed varies over time, the output of permanent magnet synchronous

generator (PMSG) which is built-in wind turbine will not be constant, in order to tackle

the input fluctuations, a diode rectifier in combination with boost converter is

implemented to achieve constant DC output voltage to the load. The MPPT algorithms

like Hill Climb method is implemented to extract the maximum power to ensure

optimum operation of boost converter by controlling the duty cycle. Thus, in order to

get DC output voltage, the PMSG is rectified using a diode rectifier ,and the rectified

22

DC voltage is used as input to the boost converter which is then rises up to the desired

level and regulated constant.

2.12 Summery of literature review

In general many researchers have been studied and published a bunch information

related to hybrid systems, some of them focused modelling PV and wind sources,

maximum point tracking systems but the aspect of synchronization of unbalanced

hybrid system is much required now days, as always needed the optimum

implementation that can be connected to the different sources and control together to

cover as much power required from the load.

Based on [24] implemented a system with PV sources connected to the grid by

using MPPT, this paper suggested inverter controlled criteria by controlling the voltage

and currents from the grid and sources, but this work is only focused one source by

lacking hybrid system

As presented in [25] published that wind-fuel combination with battery storage,

this paper managed to control DC-link voltage by the sources wind and fuel cell, but

in this work in order to compensate the DC link voltage from source and give constant

to the load, battery bank storage which can keep the reference voltage, thus this work

uses more components which is not cost effective.

In [26] proposed dual input single output DC-DC converters for stand-alone

systems. The converter is a combination of CUK and SEPIC converter called CUK-

SEPIC fused converter, The renewable energy sources are fluctuating in nature hence

the hybridization is required to overcome the fluctuating nature to an extent, the

researcher also practiced maximum point tracker strategy by using perturb and observe

method, thus this work only considered by stand-alone system which the fluctuation

nature is not much effected.

As [27] stated that A new DC-DC converter topology for hybrid wind-

photovoltaic energy system is proposed. Hybridizing solar and wind power sources

provide a realistic form of power generation. The topology uses a fusion of Cuk and

SEPIC converters. This configuration allows the two sources to supply the load

23

separately or simultaneously depending on the availability of the energy sources.

Maximum power is tracked from PV and wind energy sources using Maximum Power

Point Tracking (MPPT) algorithm. Simulation is carried out in MATLAB/ Simulink

software and the results of the Cuk converter, SEPIC converter and the hybridized

converter are presented. However this hybrid is not connected to AC side and only

studied by the DC load.

In [7] presented a paper related to hybrid PV-Wind Systems with grid-

interconnection by Fuzzy Based MPPT controller, this research uses balanced

hybridizing of PV-wind generation by using fuzzy logic strategy as maximum point

tracker and mostly related to Z-equivalent and 4-leg voltage source inverter as

controller.

24

CHAPTER 3

METHODOLOGY

3.1 Introduction

In general, to design efficient hybrid generation system requires knowledge of detailed

PV system modeling and wind turbines. In this work, a comprehensive photovoltaic

and wind turbine modeling are combined which is connected to the grid. The proposed

hybrid system combines two different sources by using power electronic converters,

and some control strategies for the inverters to hybrid and balance system.

It is known that the suggested hybrid modelling is better when the load demand

is very high and using one source is not enough, or when the areas not connected to

grid requires standalone system for generating power. In order to get best of all the

system from the source to load, all the components should be designed accurately and

optimum way. The contribution of this work is to integrate two different renewable

energy systems which has different characteristic by implementing an inverter

controlled strategy which is suitable to control common DC link voltage and grid side

voltages and currents, the proposed system also have two separate maximum point

tracker strategies which can extract maximum power from DC-DC converters from

the hybrid system, which then regulated common DC voltage can be injected to the

inverter which powers to the grid. For all the modeling is practiced by using

MATLAB/Simulink software which is very easy and near to real time tools for

modeling system application.

48

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