PS7 l9:16 lPincl . l /O7l

NOIES : * lf the thesis is CONFIDENTIAL or RESTRICTED, pleose ottoch with the letter fromihe orgonisotion with period ond reosons for confidentiolity or restriction.

UNIVERSITI TEKNOTOGI MATAYSIA

DECIARATION OI THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT

AuthOr's fuIInoME : NOR AIDA IDAYU BINTIABDULLAH

Dote of birth :21 AUGUST 1986

Title : IMPROVEMENT OF WND GENERATOR STABILfTY BY SMES

Acodemic Session : 2ffi9 I 20 | O

thot this thesis is clossified os :

CONFIDENTIAL (Contoins confidentiol informotion under the Officiol SecretAct 19721"

RESTRICTED (Contoins restricted informotion os specified by theorgonisotion where reseorch wos done)"

OPEN ACCESS I ogree thot my thesis to be published os online open occess(fulltext)

I ocknowledged ihot UniversitlTeknologi Moloysio reserves the right os follows :

1. The thesis is the property of UniversitiTeknologi Moloysio.2. The Librory of Univeniti Teknologi Mokrpio hos the right to moke copies for the purpose

of reseorch only.3. The Librory hos the right to moke copies of the thesis for ocodemic exchonge-

declore

ntla

860821-29-s492(NEW rC NO. /PASSPORT NO.)

Dote : 26 APRIL 2010

BINMAJID

Dote :26 APRIL 20lO

PROF MD

'6I hereby declare that I have read this report and in my opinion this report

has fulfills the scope and quallty for the award of degree of

Bachelor of Engineering @lectrical)"

Signature

Name of Supervisor

Date

- - - - - -Md Shah

IMPROVEMENT OF WIND-GENERATOR STABILITY BY SMES

NOR AIDA IDAYU BINTI ABDULLAH

A report submitted in fulfillment of the partial requirement for the

award of the degree of Bachelor of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

APRIL 2010

ii

“I hereby declare that all materials presented in this report is of my own work

and effort except those quotation and summaries of which I have detailed their

source”.

Signature : ..........................................

Author’s Name : Nor Aida Idayu Binti Abdullah

Date : 26 APRIL 2010

iii

To my beloved parents,

Abdullah Bin Hassan, Azizah Binti Mohamad

Brothers and Sisters,

Nor Hayati, Mohd Fairoz Izwan, Norliana

Norul Ashikin, Nor Farahiya Adlina

And all my Friends

for their encouragement.

iv

ACKNOLEDGEMENT

Praise is to Allah S.W.T., the Most Merciful and the Most Compassionate.

Peace is upon him, Muhammad, the messenger of God.

I would like to express my gratitude to my supervisor, Assoc Prof Md Shah

Majid for his valuable guidance and support throughout the two semesters until this

project completes successfully. I am grateful to Prof Dr Khalid Mohamed Nor and Assoc

Prof Dr Mohammad Yusri Hassan, for their comments and suggestions on this project.

My thanks are also extending to my fellow colleagues for sharing their ideas and

discussions. Last but not least, I would like to thanks my family and to whom that have

support me. Thank you for your motivation and moral support.

v

ABSTRACT

Energy from wind is one of the renewable energy potential sources. This energy

is one of source that can be contributed to the production of electricity on a commercial

basis. Although the energy from the wind is still a small contributor in the production of

electricity in most countries, but the development of technology and related wind

resources expected to net a lot and will enhance the role of this form of generation in the

future. Installed wind power generation capacity is continuously increasing. Wind

power is the most quickly growing electricity generation source with a 20% annual

growth for the past five years. But, the major problem is, this renewable energy

becomes not good because when the wind does not blow then the lights go out. Because

of that this project is conducted to maintain the stability of the wind turbine by using

superconducting magnetic energy storage system. This system is a very capable storage

nowadays. It can charge and discharge very fast. This project presents SMES system to

improve the stability of wind generator when the three phases occur.

vi

ABSTRAK

Tenaga dari angin merupakan salah satu sumber pembaharuan tenaga yang

berpotensi. Tenaga jenis ini merupakan salah satu sumber tenaga yang boleh

menyumbangkan penghasilan elektrik di dalam sektor komersial. Walaupun tenaga

daripada angin merupakan satu penyumbang kecil kepada penghasilan elektrik di

kebanyakan negara, tetapi pembangunan teknologi dan sumber yang berkenaan angin

dijangka akan memberi kebaikan dan peranan bentuk penjanaan ini akan meningkat pada

masa hadapan. Pemasangan penjana tenaga angin semakin meningkat. Tenaga angin

merupakan sumber penjanaan elektrik yang paling pantas berkembang dengan

pertumbuhan tahunan sebanyak 20% semenjak lima tahun kebelakangan ini. Akan

tetapi, major masalah ialah pembaharuan tenaga ini menjadi tidak bagus kerana bila

angin tidak bertiup, lampu akan terpadam. Oleh sebab itu, projek ini dibuat untuk

mengekalkan kestabilan sistem penjanaan elektrik ini dengan menggunakan sistem

penyimpanan keteradihantaran tenaga magnet. Sistem ini merupakan jenis penyimpan

tenaga yang paling cekap pada masa sekarang. Ia boleh cas dan discas dengan sangat

cepat. Projek ini menunjukkan sistem penyimpanan keteradihantaran magnet boleh

meningkatkan kestabilan penjana angin bila timbulnya kerosakan tiga fasa.

vii

CONTENTS

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATIONS iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

CONTENTS vii

LIST OF FIGURES xi

LIST OF SYMBOLS xiii

LIST OF APPENDICES xv

viii

1. INTRODUCTION

1.1 Overview 1

1.2 Problem Statement 2

1.3 Purpose of The Project 2

1.4 Objectives 3

1.5 Scope 3

1.6 Methodology 3

1.7 Wind Generator 4

1.8 Superconducting Magnetic Energy Storage 6

2. WIND POWER

2.1 History of Wind Energy 8

2.2 Types of Wind Turbine 9

2.3 Calculation for Wind Turbine 12

2.4 Calculation to Measure the Stability in Wind

Turbine

13

2.5 Conclusion 15

3. SUPERCONDUCTING MAGNETIC ENERGY STORAGE (SMES)

3.1 Introduction 14

3.2 Operation of SMES 18

ix

3.3 Calculation of Stored Energy 21

3.4 Advantages of SMES 23

3.5 Conclusion 24

4. METHODOLOGY

4.1 Introduction of MATLAB 25

4.2 Description of Related Component in SMES’s Model 27

4.2.1 Thyristor 28

4.2.2 Pulse Generator 29

4.2.3 Inductor 29

4.2.4 Three Phase AC Voltage Input 29

4.3 Description of Wind Power System’s Model 30

4.4 Description of Wind Power System Model with Fault 33

4.5 Description of Wind Power System Model with Fault and the

Adding of SMES Model

33

4.6 Run the Simulation Model 34

4.7 Conclusion 34

5. RESULTS AND DISCUSSION

5.1 Introduction 35

5.2 The Output Result for SMES’s Model 36

5.3 The Output Result of Wind Power System’s Model 38

5.4 Output Result of Wind Power System Model with Fault 39

5.5 Output Result of Wind Power System Model with Fault and 40

x

the Adding of SMES Model

5.6 Conclusion 42

6. CONCLUSSION AND RECOMMENDATION

6.1 Conclusion 43

6.2 Recommendation 44

REFERENCES 45

APPENDIX A 47

xi

LIST OF FIGURE

NO. FIGURE TITLE PAGE

1.1 The changes from wind energy to the electricity 5

1.2 The main part of the wind turbine 5

2.1 The stability of a system in term of damping ratio’s value 14

2.2 Second-order underdamped response specifications 14

2.3 Wind turbine 15

3.1 SMES operation 20

4.1 Version of MATLAB software 26

4.2 Library browser of SimPowerSystem 27

4.3 Model of SMES 28

4.4 Model of wind power system 31

4.5 Model of wind power system with fault 32

4.6 Model of wind power system with fault and the adding

of SMES model 33

4.7 Location of run button in the toolbar 34

5.1 Voltage at the superconducting coil 37

5.2 Current at the superconducting coil 37

xii

5.3 Initial state of wind power system model 38

5.4 The output waveform of the wind power system with

three phases fault 39

5.5 The output waveform of the wind power system with

three phases fault and the adding of SMES model 41

xiii

LIST OF SYMBOLS

α - Firing angle of thyristor

β - Blade pitch angle

λ - Speed ratio

ζ - Damping ratio

Cp - Power coefficient

E - Energy

f (ξ,δ) - Form function

I - Current

Ism - Inductor current

Ism0 - Initial inductor current

L - Inductance

N - Number of turn of coil

Pw - Extracted power from the wind

%OS - Overshoot in percent

ρ - Air density

R - Blade radius

Ts - Settling time

Tw - Turbine torque

Vsm - Bridge voltage

Vsm0 - Ideal no-load maximum dc voltage of the

bridge

Vw - Wind speed

xiv

ωB - Rotational speed of turbine hub

Wsm Magnetic energy

Wsm0 Initial energy in the inductor

xv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Wind turbine Characteristic 47

CHAPTER 1

INTRODUCTION

1.1 Overview

Energy from wind is one of the renewable energy potential sources. This

energy is one of source that can be contributed to the production of electricity on a

commercial basis. Although the energy from the wind is still a small contributor in

the production of electricity in most countries, but the development of technology

and related wind resources expected to net a lot and will enhance the role of this

form of generation in the future. Wind turbines used to convert energy from wind

energy to electricity. Wind turbine blades rotate and electric power obtained when

the turbine generator connected to the electricity and move it.

There are two forms of turbine most commonly used. The two types of

turbines are the horizontal type and the vertical type. The wind does not flow in

scheduled, and also, we can not expect the variation in the load demands. Therefore,

there are the needs of storage so that the electricity can be supplied to the customer

2

immediately. Besides that, this storage can save the energy that generate by the

turbine if in case there are no load demands at that time. The most suitable storage

now is the superconducting magnetic energy storage.

This type of storage is really useful, besides having a lot of advantages

compared to another type of storage. Besides that, SMES system is highly efficient

which 95% of efficiency is.

1.2 Problem Statement

Installed wind power generation capacity is continuously increasing. Wind

power is the most quickly growing electricity generation source with a 20% annual

growth for the past five years. But, the major problem is, this renewable energy

becomes not good because when the wind does not blow then the lights go out. So,

to maintain the useful of wind energy and to maintain its stability, this project is

conducted

1.3 Purpose of the Project

The purpose of this study is to design the superconducting magnetic energy

storage (SMES) model using the MATLAB software.

Besides that, this study is conducted to improve the stability in the wind

generator. The method is by using the superconducting magnetic energy storage as

storage in the wind generator. SMES can improve the stability in the wind generator

because it has a lot of advantages.

3

1.4 Objectives

The objectives of the project are to design the superconducting magnetic

energy storage model and also to improve the stability in the wind generator.

1.5 Scope

The scopes of the project are to design the SMES model using MALAB

software. Besides that, this project is conducted to simulate and analyse power

system’s stability and the effect of added SMES in a power system’s stability

1.6 Methodology

The first step is the literature review. These literature reviews are about the

wind generator, superconducting magnetic energy storage and also the components

needed to design the system.

The second step is learning about MATLAB software to design the SMES

model of the system. After design the system, the system will be simulated to get the

output so that the comparison can be made. Lastly, the system are analyzed and

comparison between power system without SMES and with SMES are made.

4

1.7 Wind Generator

Energy from wind is one of the renewable energy potential sources. This

energy is one of source that can be contributed to the production of electricity on a

commercial basis. Although the energy from the wind is still a small contributor in

the production of electricity in most countries, but the development of technology

and related wind resources expected to net a lot and will enhance the role of this

form of generation in the future. Wind turbines used to convert energy from wind

energy to electricity. Wind turbine blades rotate and electric power obtained when

the turbine generator connected to the electricity and move it.

There are two forms of turbine most commonly used. The two types of

turbines are the horizontal type and the vertical type. The wind does not flowing in

scheduled, and also, we can not expect the variation in the load demands. Therefore,

there are the needs of storage so that the electricity can be supplied to the customer

immediately. Besides that, this storage can save the energy that generate by the

turbine if in case there are no load demands at that time. There most suitable storage

now is the superconducting magnetic energy storage.

This type of storage is really useful, besides having a lot of advantages

compared to another type of storage. Besides that, SMES systems are highly

efficient which 95% of efficiency is.

In the wind turbines, the air flow into the turbine blades and turbine rotor

further through the transfer of energy from wind into mechanical energy forms. In

theory, the energy can be obtained in this process is approximately 59%. This

limitation is known as the Betz limit. In practice, the conversion efficiency is

between 35 and 45 percent because there are the other losses from components that

causing the overall efficiency becomes smaller.

Figure 1.1 shows the changes from

wind energy to the electricity and Figure 1.2 shows the main part of the wind turbine.

5

Figure 1.1 The changes from wind energy to the electricity

Figure 1.2 The main part of the wind turbine

The area that are travelled by the wind turbine rotor blades are usually in the

circle form. This area can be calculated using the formula area of a circle which is

area in meter square is equal to 3.14159 multiply with the power of two the radius of

the blades which is from the distance between the end of the rotor blades.

Besides that, power also can be obtained depending on the wind turbine rotor,

wind speed and density. The equation for the wind power in watt is area multiply

with the density and the wind speed in power of three. Lastly the answer is dividing

by two in order to calculate the wind power in watt. Density of air depends on the

height and temperature environment is usually not much affect the production of

energy from wind. This make the power in watt can be calculate by using the

equation 0.625 multiply with the area and the power of three the wind speed.

Wind power density is the parameter most commonly used and is defined as

the force per unit area of wind passed by the turbine blades. The equation can be

used to find the wind power density is 0.625 multiply with the power of three the

wind speed in meter per second.

6

1.8 Superconducting Magnetic Energy Storage

The superconductivity is a phenomenon that occurs in certain materials in

very low temperature. Its characteristic is by exactly zero electrical resistance

besides the exclusion of the interior magnetic field. This phenomenon was

discovered by Heike Kamerlingh Onnes in 1911. Superconductivity is a quantum

mechanical phenomenon just like ferromagnetism and atomic spectral lines.

The superconducting magnetic energy storage is an electrical storage.

Actually, there are three types of storage which are the mechanical energy storage,

electrochemical energy storage and the electrical energy storage. The example of the

mechanical energy storage is water pumped storage, while the example of the

electrochemical energy storage is lead-acid batteries. From the three type of the

energy storage, the electrical energy storage is the best.

The SMES system is a method of electrical energy storage. This system was

very useful besides having the highest frequency that is 97 percent and its capable of

controlling the active power flow into power systems. Besides that, SMES also has

been expected to be a significantly effective tool to enhance the power system

stability since the SMES capable of providing the active and reactive power

simultaneously and quickly for the power system.

Among the FACTS controller, superconducting magnetic energy storage is

expected to become a new effective apparatus in power system since a SMES is

capable of levelling load demand with high efficiency, compensating with load

changes, maintaining a bus voltage and stabilizing power swing.

7

Besides that, the superconducting magnetic energy storage also consists of a

magnet that levitating above the high temperature conductor. This magnet is cooled

with liquid nitrogen. The persistent electric current flows on the surface of the

superconductor to exclude the magnetic field of the magnet. This effect is called by

Meissner effect. The electromagnet will produce by the current effectively and this

electromagnet will repel the magnet.

CHAPTER 2

WIND POWER

2.1 History of Wind Energy

Winds develop when solar radiation reaches the earth, meeting clouds and

uneven surfaces and creating temperature, density and pressure differences. The

atmosphere circulates heat from the tropics to the poles, also creating winds. A

region’s mean wind speed and its frequency distribution have to be taken into

account to calculate the amount of electricity that can be produced by wind turbines

[1].

Wind machines were used in Persia as early as 200 B.C. Since the 7th

century the first practical windmills were built in Sistan, a region between

Afghanistan and Iran. These were vertical windmills. It had long vertical drive shafts

with rectangle-shaped blades. These windmills were used to grind corn and draw up

water, besides were used in the grist milling and sugarcane industries. It made of six

to twelve sails covered in reed matting or cloth material.

9

Wind power is the conversion of wind energy into a useful form of energy,

such as using wind turbines to make electricity, wind mills for mechanical power,

wind pumps for pumping water or drainage, or sails to propel ships [2]. Worldwide

nameplate capacity of wind-powered generators was 121.2 gigawatts (GW) at the

end of 2008. In 2008, wind power produced about 1.5% of worldwide electricity

usage and is growing rapidly, having doubled in the three years between 2005 and

2008. Several countries have achieved relatively high levels of wind power

penetration, such as 19% of stationary electricity production in Denmark and 11% in

Spain and Portugal.

Wind energy as a power source is attractive as an alternative to fossil fuels,

because it is plentiful, renewable, widely distributed, clean, and also did not produces

the greenhouse gas emissions.

2.2 Types of Wind Turbine

A wind turbine converts the energy of wind into kinetic energy. If the

mechanical energy is used directly by machinery, such as pumping water, cutting

lumber or grinding stones, the machine is called a windmill. If the mechanical

energy is instead converted to electricity, the machine is called a wind generator,

wind turbine, wind power unit (WPU), wind energy converter (WEC), or

aerogenerator [3].

There are two types of wind turbine. They are horizontal type and vertical

type. The types of wind turbine are depending on their rotation. Horizontal-axis

wind turbines (HAWT) have the main rotor shaft and electrical generator at the top

10

of a tower. The axis of rotation is parallel to the ground [4]. They must be pointed

into the wind and the small turbines are pointed by a simple wind vane, while large

turbines generally use a wind sensor coupled with a servo motor.

Most of these types have a gearbox, which turns the slow rotation of the

blades into a quicker rotation that is more suitable to drive an electrical generator.

HAWT rotors are usually classified according to the rotor orientation (upwind or

downwind of the tower), hub design (rigid or teetering), rotor control (pitch vs. stall),

number of blades (usually two or three blades) and how they are aligned with the

wind (free yaw o active yaw) [4].

This type of wind turbine has their advantages and also the disadvantages.

The advantages are includes the variable blade pitch, which gives the turbine blades

the optimum angle of attack. This will allow the angle of attack to be remotely

adjusted gives greater control, so the turbine collects the maximum amount of wind

energy for the time of day and season. Besides that, the tall tower base allows access

to stronger wind in sites with wind shear. In some wind shear sites, the wind speed

can increase by 20% and the power output by 34% for every 10 metres in elevation.

In the other hand, this type of wind turbine also has high efficiency, since the

blades always move perpendicular to the wind, receiving power through the whole

rotation. In contrast, all vertical axis wind turbines, and most proposed airborne

wind turbine designs, involve various types of reciprocating actions, requiring airfoil

surfaces to backtrack against the wind for part of the cycle. Backtracking against the

wind leads to inherently lower efficiency.

The second type of wind turbine is vertical axis wind turbines (VAWT). The

modern VAWT evolved from the ideas of the French engineer, Georges Darrieus,

whose name is used to describe one of the vertical-axis turbines that he invented in

1925. This device, which resembles a large eggbeater, has curved blades (each with

a symmetrical aerofoil cross-section) the ends of which are attached to the top and

bottom of a vertical shaft. VAWT have a greater solidity than HAWT, which usually

11

results in a heavier and more expensive rotor [5]. They have the main rotor shaft

arranged vertically. Key advantages of this arrangement are that the turbine does not

need to be pointed into the wind to be effective and this is an advantage on sites

where the wind direction is highly variable.

However, all the design must have their advantages and also disadvantages

including this type of wind turbine. Its advantages are include its have lower wind

start-up speeds than horizontal type and typically, they start creating electricity at 6

m.p.h. (10 km/h). Besides, this wind turbine may be built at locations where taller

structures are prohibited and it’s also having a lower noise signature. Situated close

to the ground can take advantage of locations because mesas, hilltops, ridgelines, and

passes funnel the wind and increase wind velocity.

Luckily, the stress in each blade due to wind loading changes sign twice

during each revolution as the apparent wind direction moves through 360 degrees

makes vertical wind turbine is not good. This reversal of the stress increases the

likelihood of blade failure by fatigue.

Besides that, having rotors located close to the ground where wind speeds are

lower due to the ground's surface drag, vertical wind turbine may not produce as

much energy at a given site as a horizontal wind turbine with the same footprint or

height. If the both types of wind turbine are look from this characteristic, the vertical

wind turbine has the advantages.

12

2.3 Calculation for Wind Turbine

Modeling of wind turbine rotor is complicated. According to the blade

element theory [6], [7] modeling of blade and shaft needs complicated and lengthy

computations. More over, it also needs detailed and accurate information about rotor

geometry. For that reason, considering only the electrical behavior of the system, a

simplified method for modeling the wind turbine blade and shaft is normally used.

The mathematical relation for the mechanical power extraction from the wind can be

expressed as [6], [7] Equation 2.1 below. While, Cp is taken from Equation 2.2 and

Equation 2.3.

(2.1)

(2.2)

(2.3)

When the wind velocity exceeds the rated speed, then the pitch angle of the

blade needs to be controlled to maintain the output at the rated level [6]. Now the

turbine torque, Tw, can be calculated as in Equation 2.4.

(2.4)

13

2.4 Calculation to Measure the Stability in Wind Turbine

Stability is the most important system specification. If a system is unstable,

transient response and steady state error are moot points [8]. The stability of a wind

turbine is measured by calculating the overshoot, damping ratio and also the settling

time. The overshoot is the amount that the waveform overshoots the steady state, or

final, value at the peak time and it is measured in percent. Equation 2.5 shows the

way to calculate the overshoot value in percent.

%OS = [(cmax - cfinal) / cfinal] × 100 (2.5)

Settling time is the time required for the transient’s damped oscillation to

reach and stay within plus and minus 2 percent of the steady state value, while the

damping ratio can be measured as in Equation 2.6.

(2.6)

To find the stability of the system, damping ratio is calculated. This is

because, if the value is more than 1, the system is overdamped, which is the system is

stable. If the value of damping ratio is 0, the system is undamped, which is the

system is unstable. The measure the stability of a system can be conclude in Figure

2.1. The figure shows the stability of a system in term of damping ratio’s value.

14

Figure 2.1 The stability of a system in term of damping ratio’s value

Figure 2.2 shows the response specifications of a second order underdamped

system.

Figure 2.2 Second-order underdamped response specifications.

15

2.5 Conclusion

As a conclusion, both types have their advantages and disadvantages. The

use of this types is depends on the types of wind flows at the place. Figure 2.1 shows

the example of the wind turbine.

Figure 2.3 Wind turbine

CHAPTER 3

SUPERCONDUCTING MAGNETIC ENERGY STORAGE (SMES)

3.1 Introduction

Superconducting Magnetic Energy Storage (SMES) systems store energy in

the magnetic field created by the flow of direct current in a superconducting coil

which has been cryogenically cooled to a temperature below its superconducting

critical temperature. A typical SMES system includes three parts: superconducting

coil, power conditioning system and cryogenically cooled refrigerator. Once the

superconducting coil is charged, the current will not decay and the magnetic energy

can be stored indefinitely [9].

Although their costs are high compared to other storage technologies in

respect to the costs per unit energy stored, they are cost competitive with other

flexible AC transmission system (FACTS) equipment or transmission upgrade

solutions, which are normally the competing choices. These facilities currently range

in size up to 3MW, and are generally use to provide power-grid stability in a

distribution system and power quality at manufacturing facilities with critical loads

highly susceptible to voltage instabilities [10].

17

Superconducting Magnetic Energy Storage (SMES) uses the ability of certain

materials to conduct electricity without resistance (superconductivity) to store

electrical power. In principle there is no reason why SMES couldn't be used on a

very small scale in place of conventional batteries. In practice the relatively low

energy density possible, exacting cooling requirements, and high cost, mean that

near-term applications are likely to be limited to power grid applications [11].

A common design of a SMES installation would consist of a coil of

superconducting wire buried underground, with power conditioning equipment

connecting the coil to the electricity distribution grid.

To achieve commercially

useful levels of storage, around 3,600 GJ, a SMES installation would need a loop of

around 100 miles (160 km). This is traditionally pictured as a circle, though in

practice it could be more like a rounded rectangle. In either case it would require

access to a significant amount of land to house the installation, and to contain the

health effects [11].

Superconducting Magnetic Energy Storage (SMES) systems store energy in

the magnetic field created by the flow of direct current in a superconducting coil.

This superconducting coil has been cryogenically cooled to a temperature below its

superconducting critical temperature. In a Superconducting Magnetic Energy

Storage (SMES) system, energy is stored within a magnet and it capable to release

the megawatts of power within a fraction of a cycle to replace a sudden loss in line

power.

SMES system includes three parts, they are superconducting coil, power

conditioning system and cryogenically cooled refrigerator. Once the superconducting

coil is charged, the current will not decay and the magnetic energy can be stored

indefinitely.

18

The stored energy can be released back to the network by discharging the

coil. The power conditioning system uses an inverter/rectifier to transform

alternating current (AC) power to direct current or convert DC back to AC power.

The inverter/rectifier accounts for about 2-3% energy loss in each direction. SMES

loses the least amount of electricity in the energy storage process compared to other

methods of storing energy. SMES systems are highly efficient; the round-trip

efficiency is greater than 95% [12].

3.2 Operation of SMES

Superconducting magnetic energy storage (SMES) is a large superconducting

coil capable of storing electric energy in the magnetic field generated by DC current

flowing through it [4], [13]. The real power as well as the reactive power can be

absorbed by or released from the SMES coil according to system power requirements.

Since the successful commissioning test of the BPA 30 MJ unit [4], [14], SMES

systems have received much attention in power system applications, such as, diurnal

load demand leveling, frequency control, automatic generation control,

uninterruptible power supplies, etc [4].

SMES is a relatively simple concept as an energy storage device. It stores

electric energy in the magnetic field generated by DC current flowing through a

coiled wire. The magnetic energy would be dissipated as heat due to the wire's

resistance to the flow of current if the coil were wound using a conventional wire

such as copper. However, if the wire is superconducting that means no resistance,

and then energy can be stored in a "persistent" mode, virtually indefinitely, until

required.

19

In order to eliminate the ohmic heat dissipation, the superconductors have

zero resistance to DC electrical current at low temperature; hence the refrigerator is

needed in the SMES to cool the coil. In AC applications, there are still electrical

losses, but these losses can be minimised through appropriate wire architecture and

the device design. For both DC and AC applications, energy savings will be

significant.

In SMES operation, energy is stored directly in a superconducting magnetic

energy storage system. It is able to store energy with a loss of only 0.1% per hour

compared to a loss of about 1% per hour loss for flywheels. But this is required for

the SMES’s cooling system. From this research, it is claimed that SMES is 97-98%

efficient and it is much better at providing reactive power on demand. Until now,

SMES have only operated on a relatively small scale. However, projects have been

started with SMES on a much commercially larger scale. This is very beneficial, as

the unit cost of SMES facilities will decrease as the size increases. At this point

SMES systems are able to store up to about 10 MW and some research groups have

achieved much higher capacities of hundreds of MW, but only for a second.

However, some researchers believe SMES can potentially store up until 2000 MW.

Theoretically, a coil of around 150-500 m radius would be able to support a

load of 5000 MWh, at 1000 MW and this depending on the peak field and ratio of

the coil's height and the diameter. Recent developments have tried to use silicone-

based three-phase adjustable speed motor drives (ASDs) because it can bring down

the scale of SMES to fit into lorry trailers.

In the standby mode, the current continually circulates through the normally

closed switch of the voltage regulator and power supply, and back to the magnet.

The power supply provides a small trickle charge to replace the power lost in the

20

non-superconducting part of the circuit. When a voltage disturbance is sensed, the

controller directs real and reactive power from the inverter to the load, while

automatically opening the solid-state isolation switch within two milliseconds.

When the voltage across the capacitor bank reaches a pre-set level, the switch closes.

This sequence repeats until normal voltage from the utility feeder is stored. This

systematic transfer of energy from the magnet to the load keeps the load interruption

free for optimum performance of critical processes.

The SMES can recharge within minutes and can repeat the process of charge

and discharge process in sequence thousand of times without any degradation of the

magnet. The recharge time can be accelerated to meet specific requirement,

depending on the system capacity. The Figure 3.1 shows the operation of the SMES

system.

Figure 3.1 SMES operation

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3.3 Calculation of Stored Energy

The magnetic energy stored by a coil carrying a current is given by one half

of the inductance of the coil times the square of the current [9]. The Equation 3.1

below is the equation to calculate the magnetic energy stored by a coil.

(3.1)

where E = energy measured in joules

L = inductance measured in henries

I = current measured in amperes

If a cylindrical coil with conductors of a rectangular cross section is

considered, the mean radius of coil is R while a and b are width and depth of the

conductor. f is called form function which is different for different shapes of coil. ξ

(xi) and δ (delta) are two parameters to characterize the dimensions of the coil.

Therefore the magnetic energy stored in such a cylindrical coil as shown below. This

energy is a function of coil dimensions, number of turns and carrying current [9].

The Equation 3.2 is shows the way to calculate energy if the rectangular cross section

in a cylindrical coil is considered.

(3.2)

where E = energy measured in joules

I = current measured in amperes

f(ξ,δ) = form function, joules per ampere-meter

N = number of turns of coil

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For initial charging of the SMES unit, the bridge voltage Vsm is held constant

at a suitable positive value. The inductor current Ism rises exponentially and

magnetic energy Wsm is stored in the inductor. When the inductor current reaches its

rated value Ism0, it is maintained constant by lowering the voltage across the inductor

to zero. The SMES unit is then ready to be coupled to the power system for

stabilization. It is desirable to set the rated inductor current Ism0 such that the

maximum allowable energy absorption equals the maximum allowable energy

discharge [15]. The voltage Vsm of the dc side of the converter is expressed by the

Equation 3.3 below.

Vsm = Vsm0 cos α (3.3)

The current and voltage of superconducting inductor are related as in the

Equation 3.4 below.

(3.4)

The real power Psm absorbed or delivered by the SMES can be given by Equation 3.5

(3.5)

Since the bridge current is not reversible, the bridge output power Psm is

uniquely a function of , which can be positive or negative depending on Vsm . If Vsm

is positive, power is transferred from the power system to the SMES unit, while if

Vsm is negative, power is released from the SMES unit [15]. The energy stored in the

superconducting inductor is given in Equation 3.6 and Wsm0 is given in Equation 3.7.

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(3.6)

(3.7)

3.4 Advantages of SMES

There are several reasons for using superconducting magnetic energy storage

instead of other energy storage methods. The most important advantage of SMES is

that the time delay during charge and discharge is quite short. Besides that its power

is available almost instantaneously and very high power output can be provided for a

brief period of time.

In addition, the other energy storage methods, such as pumped hydro or

compressed air have a substantial time delay associated with the energy conversion

of stored mechanical energy back into electricity. Thus if a customer's demand is

change immediately, SMES is the best methods of storage. It can charge and

discharge very fast compared with another storage method.

The other advantage of SMES is its loss of power is less than other storage

methods. This is because electric currents encounter almost no resistance. In

addition, the main parts in a SMES are motionless, which will results in high

reliability if it is chosen as a storage method in a power system.

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3.5 Conclusion

After the research about superconducting magnetic energy storage including

their advantages and also their operation, it can be conclude that this storage is more

capable as a storage in a power system compared with another storage.

CHAPTER 4

METHODOLOGY

4.1 Introduction of MATLAB

MATLAB is software that has high-performance language for technical

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

environment where problems and solutions are expressed in familiar mathematical

notation. Suitable with its name as matrix laboratory the MATLAB software typical

use include in math and computation, algorithm development, data acquisition,

modelling, simulation and prototyping, data analysis, exploration, and visualization,

scientific and engineering graphic, and also in application development, including

graphical user interface building.

MATLAB was originally developed by the LINPACK and EISPACK

projects. It was written to provide easy access to matrix software and today,

MATLAB engines incorporate the LAPACK and BLAS libraries, embedding the

state of the art in software for matrix computation. MATLAB uses a high level

programming language and include control flow statements, data structures,

input/output, and object oriented programming features. MATLAB also provides

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facilities for managing variables, importing and exporting data and tools for creating

and debugging programs [16]. Figure 4.1 shows the version of MATLAB software

that has been used in this project.

Figure 4.1 Version of MATLAB software

In this project, the MATLAB software will be use to design the model of

superconducting magnetic energy storage using SimPowerSystem.

SimPowerSystems™ extends Simulink® software with tools for modelling and

simulating basic electrical circuits and detailed electrical power systems. By using

these tools, the model of the generation, transmission, distribution, and consumption

of electrical power can be modelled. Besides, conversion into mechanical power

also can be modelled.. The SimPowerSystems product is well suited to the

development of complex, self-contained power systems, such as those in automobiles,

aircraft, manufacturing plants, and power utility applications. Figure 4.2 shows the

library browser of SimPowerSystem in the MATLAB software.

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Figure 4.2 Library browser of SimPowerSystem

In this project, the MATLAB software is used to model and simulate the

model of:-

a) Wind power system

b) Wind power system with three phase fault

c) Superconducting magnetic energy storage (SMES)

d) Wind power system with three phase fault and adding of superconducting

magnetic energy storage’s model

4.2 Description of Related Component in SMES’s Model

In this project, there are several components have been used for completing

the model especially the type of thyristor that have been used to design the bridge

28

converter for the model of superconducting magnetic energy storage. So, the

understanding on the component characteristic and their setting are very important in

order to build up the model. It is because, by selecting the wrong component, the

whole circuit will not function and it takes too long time to figure out the problem.

Figure 4.3 shows the model of SMES.

Figure 4.3 Model of SMES

4.2.1 Thyristor

There are two types of thyristor in the MATLAB. They are the basic

thyristor and the detailed thyristor. The difference between these two thyristor is

their characteristic. In this project, there are six basic thyristor is use to create the

thyristor converter of the superconducting magnetic energy storage’s model. The

inputs of the bridge converter are the voltage source and also the gate signal to turn it

on and off. The outputs for bridge converter are the positive and negative pin. The

converter impresses positive or negative voltage on the superconducting coil.

Charge and the discharge process are easily controlled by simply changing the delay

angle α that controls the sequential firing of the thyristor. If α is less than 90°, the

29

converter operates in the rectifier mode (charging) and if α is greater than 90°, the

converter is operates in the inverter mode (discharging).

4.2.2 Pulse Generator

In SMES model also, there is the six pulse of pulse generator. This

component is used to generate the square wave pulse at regular intervals. This was

use as the input of the thyristor converter. Without pulse generator, the thyristor

converter will not function. The input for this component is the phase angle and the

three phase of voltage source. The figure below shows the model of pulse generator.

4.2.3 Inductor

Inductor in this model is use as the superconducting coil. Its function is in

the charging and discharging process. The rated value of the inductor is important in

the model because the maximum allowable discharge energy must be equal to

allowable charge energy.

4.2.4 Three Phase AC Voltage Input

This ac voltage input is used to supply to current so that the component in the

model can be successfully operate. The three phase input is used because the wind

power system in this project is in three phase. Because of that, three phase input is

used.

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4.3 Description of Wind Power System’s Model

A generic model of the High-Penetration, No Storage, Wind-Diesel

(HPNSWD) system is presented in this project. The model from demo in MATLAB

is used. The HPNSWD system presented in this demo uses a 480 V, 300 kVA

synchronous machine, a wind turbine driving a 480 V, 275 kVA induction generator,

a 50 kW customer load and a variable secondary load (0 to 446.25 kW). At low

wind speeds both the induction generator and the diesel-driven synchronous

generator are required to feed the load. When the wind power exceeds the load

demand, it is possible to shut down the diesel generator. In this all-wind mode, the

synchronous machine is used as a synchronous condenser and its excitation system

controls the grid voltage at its nominal value. A secondary load bank is used to

regulate the system frequency by absorbing the wind power exceeding consumer

demand.

The Secondary Load block consists of eight sets of three-phase resistors

connected in series with GTO thyristor switches. The nominal power of each set

follows a binary progression so that the load can be varied from 0 to 446.25 kW by

steps of 1.75kW. GTOs are simulated by ideal switches.

The frequency is controlled by the Discrete Frequency Regulator block. This

controller uses a standard three-phase Phase Locked Loop (PLL) system to measure

the system frequency. The measured frequency is compared to the reference

frequency (60 Hz) to obtain the frequency error. This error is integrated to obtain the

phase error. The phase error is then used by a Proportional-Differential (PD)

controller to produce an output signal representing the required secondary load

power. This signal is converted to an 8-bit digital signal controlling switching of the

eight three-phase secondary loads. In order to minimize voltage disturbances,

switching is performed at zero crossing of voltage. Figure 4.4 shows the model of

wind power system.

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Figure 4.4 Model of wind power system

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4.4 Description of Wind Power System Model with Fault

The three phase fault is added in the wind power system to analyse the power

and the reactive power of the wind power system without fault and with fault. Figure

4.5 shows the model of wind power system with fault.

Figure 4.5 Model of wind power sistem with fault

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4.5 Description of Wind Power System Model with Fault and the Adding of

SMES Model

The SMES model is added in the model of wind power system with fault to

analyse the effect of SMES model in the system. Figure 4.6 shows the wind power

system model with fault and the adding of SMES model.

Figure 4.6 Model of wind power system with fault and the adding of SMES model

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4.6 Run the Simulation Model

In order to get the result after complete the circuit design, setting and

requirements, the user need to run the circuit. To run the simulation, simply click on

the run button in the toolbar. Figure 4.7 shows the location of run button in the

toolbar. When this button is clicked, the MATLAB software will go through several

stages of processing the circuit before starting the simulation. The output of the

model can be seen by clicking the scope block in the model after the simulation is

completely run.

Figure 4.7 Location of run button in the toolbar

4.7 Conclusion

By understanding all main components in the MATLAB software and also

the step for build up the circuit, it can reduce the chances of failure for running

circuit. Moreover, it also will reduce the number of component when doing the

complicated circuit. Chapter 5 will discuss on the result that obtained from the

MATLAB simulation and it will be compared with the theoretical in the chapter 2

and chapter 3.

CHAPTER 5

RESULTS AND DISCUSSION

5.1 Introduction

There are four main parameters that used to see the improvement of wind

generator stability. They are the power at the wind turbine, the power at the

secondary load, the power at the main load, and also the reactive power at the

synchronous condenser. Even though the discussion just focusing in specific type of

characteristic of the stability in wind power system model and the specific location of

the fault, the user can use the simulation circuit in this project to test and get others

measurement in another location. So, the results of waveform that has been obtained

from MATLAB simulation will be discuss in term of the stability in the wind turbine,

in order to compare with the theoretical.

The stability of a wind turbine can be measured by calculate the settling time

of the power and the reactive power of the wind turbine. The settling time is the time

required for the transient’s damped oscillations to reach and stay within plus and

minus 2% of the steady state value after the disturbance occur. In this project, the

36

disturbance that has been used is the three phase fault. So, in order to improve the

stability of the wind turbine, the minimum of settling time is needed.

Besides the settling time, the percentage of overshoot is also need to take care

of in order to improve the stability of the system. The percentage of overshoot, OS%

is the amount that the waveform overshoots the steady state, or final, value at the

peak time, expressed as a percentage of the steady state value. The output of the

SMES model also will be discussed in this chapter.

5.2 The Output Result for SMES’s Model

The waveforms of the SMES model have been obtained from the simulation

result using MATLAB software. The voltage output and the current output have

been measured at the superconducting coil. The current has been measured by

adding the current measurement between the superconducting coil and the positive

output pin at the thyristor converter. While, the voltage has been measured by added

the voltage measurement, parallel with the superconducting coil in the SMES model.

Figure 5.1 shows the result of voltage at the superconducting coil, while the Figure

5.2 shows the result of the current at the superconducting coil.

37

Figure 5.1 Voltage at the superconducting coil

Figure 5.2 Current at the superconducting coil

The result shows the charging and discharging of the superconducting coil

depending on α setting at the thyristor converter. Based on the theoretical, if α is less

than 90°, the converter operates in the rectifier mode (charging) and if α is greater

than 90°, the converter is operates in the inverter mode (discharging). The results

from the simulation on the MATLAB prove the theoretical.

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5.3 The Output Result of Wind Power System’s Model

The result at the initial state of the model of the power system is stable before

the disturbance. Figure 5.3 shows initial state of the wind power system model. Each

parameters of this output have different value of damping ratio, settling time and

overshoot in percent. For the power in wind turbine, the OS% is equal to 12.5%

while the ζ is equal to 0.55. The settling time of wind power system model is 2.5

second. Besides that, the OS% in the power of secondary load and in the reactive

power in synchronous condenser is 23% and 25% for each. From the OS% value,

the ζ for each parameter are 0.423 and 0.403.

Figure 5.3 Initial state of wind power system model

39

5.4 Output Result of Wind Power System Model with Fault

Figure 5.4 shows the result of power and the reactive power in wind power

model with the added of three phase fault. The result shows that the stability of the

wind power system is decreased. The decreasing of the stability because when the

three phases fault was added in the system, the voltage at the fault will become zero.

In the other hand, the voltage through arc will be of a very small value. A fault will

cause currents of high value to flow through the network to the faulted point.

Figure 5.4 The output waveform of the wind power system with three phases fault

40

The result in Figure 5.4 shows the OS% for the power in wind turbine is 40%

while the ζ is 0.28. Besides that, settling time for this parameter is 4 second. From

Figure 5.4 also shows that the value OS% in the power of secondary load and in the

reactive power in synchronous condenser is 58% and 900% for each. From the OS%

value, the ζ for each parameter are 0.171 and -0.57.

Based on the Figure 5.3 and Figure 5.4, it can be conclude that the settling

time and the percentage of the overshoot for each parameter in Figure 5.4 were

greater than the settling time and the percentage of the overshoot in the output

waveform at the Figure 5.3. This simulation result proved that the system with three

phases fault is less stable than the system without any fault in the theoretical.

5.5 Output Result of Wind Power System Model with Fault and the Adding

of SMES Model

The SMES model is added in the model of wind power system with fault to

analyse the effect of SMES model in the system. In the theoretical, the stability of

the system with SMES must be stable than the system without SMES. Figure 5.5

shows the output result of wind power system model with fault and the adding of

SMES model.

Based on Figure 5.5, the values for OS%, ζ, and Ts are exactly same as the

value in Figure 5.4. So, it can be conclude that there are no stability change between

a powers system without SMES and a power system with the added of SMES. This

result does not follow the theoretical.

41

Figure 5.5 The output waveform of the wind power system with three phases fault

and the adding of SMES model

42

5.6 Conclusion

Based on result obtained, it shows there are failures occur in this project.

Based on the theoretical, the stability in wind turbine should improve when the

SMES circuit is added in the power system circuit with fault, but in this project the

improvement of the stability can not be prove. There are many reason of this failure

such as the value of inductor in SMES model is not suitable. It is important to make

sure the inductor value is suitable because the maximum allowable energy charges

must be equal to the maximum allowable energy discharge.

Besides that, the using of Demo circuit in the MATLAB is also one of reason

why is the failure occurring. It is important to change all the parameters

characteristic of the component to match with the original model.

CHAPTER 6

CONCLUSION AND RECOMMENDATION

6.1 Conclusion

MATLAB software is very useful in term of design the electrical power

system besides analysing the model. It will give a closely similar result with the

theoretical concept. By referring to the waveform are enough to determine the

stability of the power system without doing the calculation. It makes the user can

know the stability of a power system in a very short time.

Furthermore, the SMES circuit is very important in this project. It is

important to make sure this model can be simulated successfully. The main part in

this model is the thyristor converter because it is important to set α as 90°. If α less

than 90°, the model will operate in rectifier mode which is charging. If α greater

than 90°, the model is operates in inverter mode or it also can be called as

discharging process.

44

Besides, the value of superconducting coil is also important to make sure that

the maximum allowable charge energy is equal to the maximum allowable charge

energy.

6.2 Recommendation

In completing this project, there are some problems encountered and several

suggestions are made based on these problem. In order to do improve the stability of

wind generator, the SMES model is the most important part. In this model, the right

value of inductor must be set because to make sure the maximum allowable charge

energy is equal to the maximum allowable discharge energy.

Furthermore, based on the research, the stability of the wind generator can be

improved by controlled the firing angle of the SMES by using the better controller

such as by using PI controller, Fuzzy Logic controller or artificial Neural Network

(ANN) controller.

Lastly, the MATLAB software is very user friendly software. The user just

need to drag or copy the component that has been given in the library, connect and

editing the parameter in order to build up complete circuit. Even though it very

useful, but the user need take a very long time for understand to use it. Furthermore,

the help function and the tutorial will not very useful because it is do not given the

instruction step by step.

45

REFERENCES

1. Dirk ABmann, Ulrich Laumanns and Dieter Uh, Renewable Energy: A Global of

Technologies, Policies and Markets, EARTHSCAN, 2006

2. http://en.wikipedia.org/wiki/Wind_power

3. http://en.wikipedia.org/wiki/Wind_turbine

4. Mohd Hasan Ali, Minwon Park, In-Keun Yu, Toshiaki Murata, Junji Tamura and

Bin Wu, Enhancement of transient stability by fuzzy logic-controlled SMES

considering communication delay, International Journal of Electrical Power &

Energy systems (IEEE Xplore), 2009, p.p 402-408

5. Godfrey Boyle, Renewable Energy, OXFORD UNIVERSITY PRESS, 2004

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Tamura, Transient Stability Enhancement of Wind Generator Using

Superconducting Magnetic Energy Storage Unit, International Conference on

Electrical Machines, 2008

7. S.Heier, Grid Integration of Wind Energy Conversion System, John Wiley &

Sons Ltd., Chicester, UK(1998)

46

8. Norman S. Nise, Control System Engineering (Fourth Edition), JOHN WILEY

& SONS, INC, 2004, p.p 325

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10. Richard Baxter, Energy storage: a nontechnical guide, PENNWELL, 2006

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ml

12. Cheung K.Y.C, Cheung S.T.H, Navin De Silvia R.G, Juvonen M.P.T, Singh R,

Woo J.J. Large-Scale Energy Storage Systems. Imperial College London: ISE2,

2002/2003

13. R.J. Abraham, D. Das and A. Patra, Automatic generation control of an

interconnected hydrothermal power system considering superconducting

magnetic energy storage, Int J Electron Power Energy Syst, 2007

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administration 30 MJ superconducting magnetic energy storage unit, IEEE

Trans Power Apparatus Syst, 1985

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Superconducting Magnetic Energy Storage for Transient Stability Augmentation,

IEEE Transaction on Control System Technology , January 2007

16. Muzlifah Mohd Ali, Introduction to MATLAB, Program Pengajian

DiplomaUniversiti Teknologi Malaysia Kuala Lumpur, 2003

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APPENDIX A

Wind turbine characteristics

Figure A.1 Wind turbine characteristic