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THESIS REPORT
On

DESIGNING OF STAND ALONE
SMALL SCALE WIND TURBINE
FOR
BATTERY CHARGING APPLICATION
Topic Number and Name
ENGR 9700(A-D) Master Thesis
Semester and Year
Semester 1-2021

Student Name and ID:
Chandanpreet Kaur (2223527)

Name of Project Supervisor
Dr Amin Mahmoudi
(Electrical Engineering)
Name of Co-Supervisor
Mr
...


Chandanpreet Kaur
June 2021

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Executive Summary
The increase in fossil fuel costs and global warming issues lead to the popularity of renewable
energies
...
In small-scale power plants, consumers are storing
the additional generated energy in a battery pack
...
Therefore, a controller is required when the generated energy is
stored in the battery
...
The permanent magnet synchronous generators (PMSGs) are usually utilized in smallscale wind generators due to their high power density
...
1kW wind turbine
equipped by PMSG is investigated for the design of the charge controller
...
A
12V 30Ah battery package and 150W constant load is assumed as the loads of the system
...
Both the constant load and battery package are supplied through a constant DC-link
where a boost converter provides a regulated voltage for the constant load, the main power
converter of the charge controller is a buck converter
...
The control loops of these
converters are optimally designed to deliver the power with a regulated voltage
...
The results demonstrate the designed controller can deliver the required power
properly to the load and battery package
...
2
Executive Summary
...
6
List of Tables
...
8
1
...


Project background and Motivation
...
2
...
9

1
...


Objectives of project
...
4
...
10

Chapter 2: - Literature review
...
14
3
...


Wind turbine
...
1
...

a
...
14
Wind power:
...


Blade swept area
...


Air density
...
1
...


Classification of wind turbine
...


Horizontal-axis and vertical axis wind turbine:
...


Upwind and downwind wind turbines:
...


Direct drive and geared drive wind turbines:
...


On grid and off grid wind turbines:
...


Onshore and offshore wind turbines:
...
1
...


Wind turbine Configuration:
...
1
...


Wind power parameters:
...


Power coefficient
...


Tip speed ratio
...


Wind turbine capacity factor
...
1
...


Wind Turbine used in project
...
2
...
23

a
...
23
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b
...
24

c
...
26

3
...
1
...
31

Chapter 4: Power Electronic Circuits and energy storage system required for wind energy
conversion system
...
1
...
33

a
...
34

b
...
37

c
...
39

4
...


Energy Storage System
...
2
...


Types of electrochemical batteries
...
2
...


Battery condition
...
2
...


Control strategies for keeping voltage of battery constant
...
2
...


Battery and control scheme used for project
...
49
5
...


Wind turbine Mathematical model: -
...
2
...
50

5
...


Buck converter Mathematical model: -
...
4
...
53

Chapter 6: Simulations and Results for wind energy conversion system
...
63
REFERENCE
...
66
a)

Wind turbine system specification
...
66
c)

Rectifier specifications
...
66
e)

Battery specifications
...
67

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List of Figures
Figure (1-1): - block diagram of wind energy conversion system for this project
...
16
Figure (3-3): - Schematic of upwind, three-bladed HAWT, and downwind, two-bladed HAWT 17
Figure (3-4): - Internal structure of direct drive and geared drive wind turbine
...
19
Figure (3-6): - parts and components which are required for vertical axis wind turbine
...
22
Figure (3-8): -Turbine power characteristics with set parameters of turbine
...
24
Figure (3-10): - Cutaway diagram of doubly fed induction generator (Wenping Cao, March
2012)
...
27
Figure (3-12): - Cutaway diagram of permanent magnet synchronous generator (Wenping Cao,
March 2012)
...
31
Figure (3-14): - Parameters of permanent magnet synchronous machine in Matlab for project
...
34
Figure (4-16): - Circuit diagram of three phase bridge rectifier (Rashid, 2014)
...
36
Figure (4-18):- Circuit diagram for buck converter (Rashid, 2014)
...
40
Figure (4-20):- Equivalent circuit diagram of buck converter for mode 2 operation (Rashid,
2014)
...
41
Figure (4-22): - Image depicting the constant voltage control
...
46
Figure (4-24):- Parameters set for battery for wind energy conversion system
...
48
Figure (5-26):characteristics of a wind turbine for different values of pitch angle
...
r
...
electrical angle of rotor
...
52
Figure (5-29): - Schematic diagram of charging control (Her-Terng Yau, 2012)
...
55

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Figure (6-31): - the Simulink model of Wind energy conversion model for charging a battery in
MATLAB
...
57
Figure (6-33): - Waveform of variable DC voltage of around 12
...
57
Figure (6-34): - Simulink model of Buck converter with battery charger
...
58
Figure (6-36):- Boost converter for applying a double voltage than the input voltage to a constant
load
...
60
Figure (6-38): - Result of battery voltage for wind speed of 15m/s and a constant load of 5 ohm
supplied with the help of boost converter
...
62

List of Tables
Table 1: Advantages and disadvantages of SCIG-WECS and PMSG-WECS
...
30

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Chapter 1: Introduction and Background
1
...


Project background and Motivation

In earlier times, the non-renewable energy sources, like fossils fuels (coal, oil, and natural gas),
were used for the generation of electricity and have made a larger portion in today’s energy
market
...
Also, fossil fuels
consumption is one of the main reasons of the earth pollution and global warming
...
Wind energy has emerged as a major form for green energy generation
among its counterparts such as solar and water power plants
...

With the advancement in the technology and the reduction in the prices of the wind energy, over
the last 20 years, has made this energy source as most affordable one and made it possible to
generate the electricity with the help of this energy source that can be further used in the
residential areas
...
Off grid or stand alone small wind turbine
provides a very attractive source of energy for remote communities and small business due to its
benefit of reducing the stress on grids by eliminating the pollution, reducing the cost incurred on
the fuel used for diesel generators which are not used in standalone systems
...

Moreover the standalone wind turbines can be installed where the source of wind is enough or
the connection to grid is very costly
...

With the help of the wind turbine system, the wind energy can be used to generate electricity
which can be further stored for the usage in the houses
...
The advantage of using the wind energy to generate
electricity, for usage in household items, is that it works effectively in any weather condition
without any consumption of fossil fuels and the electricity is also available at night time with the
help of charged batteries
...

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1
...


Thesis Report

Method

The main focus of this project/thesis is to design and analyze a 1
...
For designing a small scale wind
turbine which will be used to generate the electricity for battery charging application, a wind
turbine with a permanent magnet generator will be used in this project because of their high
efficiency
...
Now this generated electricity cannot be directly used in the
residential houses, so here comes the need for power electronics in terms of power converter that
will be used to convert this electricity to appropriate voltage
...
The dc/dc converters in the wind turbine
system can be of any type either buck converter, boost converter or buck-boost converter
...
After converting the electricity to the required levels, the batteries can be used to store
this power that would be required for the residential use further
...
This controller will be used to control the duty cycle of the
Pulse width modulation signal required to turn on the switching devices of the converter based
on the values of the error signal generated using the difference of the reference voltage and
output voltage of the converter
...


1
...



Objectives of project
The main aims of this project are to get a working knowledge of the wind turbine that is
required to convert the kinetic energy of the wind into electricity
...




Along with this goal, another objective is to design the power electronic circuits that are
required to convert the generated electricity to required level of voltage and of required
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form which includes designing of link capacitor between the rectification and the
converter stage and the designing of the inductor and capacitor of buck converter used
...
The estimated block diagram of the project is given in
figure (1-1)
...
4
...
It
gives the information about the methods used to implement a model of standalone wind turbine
system of 1
...
The aim or objectives of the project along with the outline of the
thesis are also included in this chapter
...


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Chapter 3: Wind Energy Conversion system and its component, Wind turbine and
Generators
This chapter first gives the general information about the wind turbine
...

The parameters of the Simulink wind turbine model are also described in the end of the section
...

Chapter 4: Power Electronic Circuits and energy storage system required for wind energy
conversion system
This chapter provides the information of different power electronic circuit used for the wind
energy conversion system
...
After this
the energy storage system were explained mainly indicating the properties and charging methods
of the battery
...
The models were also used to determine the values of the components
of the power electronic circuits
...


Chapter7: -Conclusion and Future Work
This chapter provides the conclusion of this project based on the results obtained in previous
section
...

According to the Global wind energy Council (GWEC) report, total capacity of the wind energy
has increased to 44 GW worldwide, till 2021
...
Same like
these cities Canada also plans to have 20 % of demand supplied by the wind energy till 2025
...

A large number of research and development has been done on the wind energy conversion
system for a Grid connected WECS based on the type of generators and power converters used
...
So, he has provided
various advantages of using the stand alone system as compared to grid connected system
...

The main component used to convert the kinetic energy of the wind to the mechanical energy is
wind turbine
...
Based on the advantages that the horizontal axis wind turbine
was providing, it was selected for this project
...
Author has
conducted the study in paper based on the efficiency, reliability, cost, operation and maintenance
requirement, excitation requirements and noise level associated with each type
...

For the power converters the circuits mentioned in (S
...
The variable DC voltage was generated
using the bridge rectifier discussed in (S
...
To stabilize this variable Dc a buck
converter was used in this project
...
At the output of the Buck converter a DC voltage is available to
store in some form which can be further used in households
...
Based on the advantages of battery energy storage system discussed
in paper a battery was used to store the electricity in electrochemical form
...
For control scheme, a
Battery charger with a buck converter described in (Her-Terng Yau, 2012) was used for this
project in which a proportional integral controller was using a battery voltage and reference
voltage to generate an error signal for producing a duty cycle for the buck converter
...
Then this equation was used in paper to calculate the value
of the gains of PI controller using Routh array table
...
The details about these components are
given below
...


3
...


Wind turbine

Wind turbines are used to generate electricity from wind energy
...
It was equipped with
144 cedar blades with a rotating diameter of 17 m
...


3
...
1
...
It is a special form of kinetic energy in air as it flows
...
Wind power:
Power in wind which is moving is a flow rate of the kinetic energy in wind per second in
watts where kinetic energy is given as KE= ½ * (m

) in which m is the mass of the air and

V is the speed
...
Blade swept area
The swept area of the blades also determines the output power of the wind turbines
...
, 2018)
...

c
...
The density of the wind varies
with temperature and pressure and is calculated from the following state of equation
...


The temperature and pressure both varies with the height and the following equation depicts
the combined effect on air density
...
1
...
Classification of wind turbine
Wind turbines can be classified according to different parameters such as turbine generator
configuration, airflow path relative to turbine rotor, turbine capacity, power supply mode
and location of turbine installation
...
Besides these types another classification of wind turbines are direct drive and
geared drive wind drive, on-grid and off grid wind turbine and the last one is onshore and off
shore wind turbines
...


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a
...
Due to this type of configuration of blades
these turbines provide higher efficiency, higher power density, low cut-in speed and low
cost per unit power output
...
r
...
The main benefit of these types of wind turbine is that it can accept
wind from any direction which eliminates the use of yaw control
...
But an external energy source
is required to rotate the blades during the initial stage
...

In comparison to horizontal-axis turbine these type make up a small percentage of wind
turbine due to lower wind power efficiency
...


Image removed due to copyright restriction
...
Upwind and downwind wind turbines:
Generally a horizontal axis wind turbines are classified into these two categories
...
In these turbines
the rotors face the wind and the main advantage of these types of turbines is to avoid the
distortion of the flow field as the wind passes through the wind tower and nacelle
...
This also enables blades to be made more flexible
...
The blades of the downwind turbines
also make impulsive or thumping noises sometimes
...


Image removed due to copyright restriction
...
Direct drive and geared drive wind turbines:
Generally to increase the speed of the rotor of the generator to get a higher output power a
multistage gearbox is used
...
Besides this, the usage of gearbox also reduces

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the reliability of the turbine and increases the mechanical losses and noise levels (Tong,
2010)
...
These turbines are more superior to the geared drive turbines
in terms of energy efficiency, reliability and design simplicity (Tong, 2010)
...


Image removed due to copyright restriction
...
On grid and off grid wind turbines:
Most of the medium size and large size wind turbines are connected to the grids for the
different applications
...

On the other side, all the small wind turbines are of type off-grid wind turbines which are
mostly used for residential homes, farms, telecommunication and other applications
...
Therefore these turbines are used with batteries,
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diesel generators and photovoltaic systems to improve the stability of supplied power by the
turbine
...
Onshore and offshore wind turbines:
On shore turbines have a long history of their development which provides the number of
advantages which includes easier integration to grid network, lower cost of foundation,
tower building and turbine installation
...
Along with
these advantages, in case of offshore wind turbines the turbine noise is no longer an issue
...
1
...
Wind turbine Configuration:
Most of the wind turbines nowadays are of horizontal axis type with three blades typically
...
It is positioned on the top of the wind tower
...


Image removed due to copyright restriction
...


Image removed due to copyright restriction
...
It
generally requires a guide wire which is used to keep the shaft of the rotor in position
...
These rotors blades are
generally a part of rotor which takes the kinetic energy of the wind and converts that to the
rotation of the hub; where rotor is a heart of wind turbines, responsible for capturing the
energy of the wind and transforms that energy to mechanical energy
...
The main function of the gear box is to increase the speed achieved
using the shaft to further increase the speed of the generator
...
, 2013)
...
1
...
Wind power parameters:
a
...
This parameter generally deals
with the conversion of the energy in the first stage which involves the conversion of kinetic
energy to mechanical energy to run the shaft of wind generator
...

(3-5)
b
...

(3-6)
Where l is the length of blade, r is the radius of blade and

is the angular speed of blades
...

(3-7)
c
...

So the capacity factor of the wind turbine is used to determine the measure of the actual
power output of the wind turbine in a given period divided by its power output if the turbine
has operated the entire time (Tong, 2010)
...
25 and 0
...
1
...
Wind Turbine used in project
In this project already provided wind turbine model in Simulink was used which was
implementing a variable pitch wind turbine model
...
1 kW
because of its benefits that it was providing in comparison to its counterpart Vertical axis
wind turbine
...
The
turbine power characteristics with the set parameters (shown in figure (3-7)) is shown in
figure (3-8) which was providing maximum power of 1100 W at base wind speed of
12m/sec
...
2
...
Generally, there are three main types of generators that can be used
with various wind turbine systems which are AC (alternating current) synchronous, DC (Direct
current) and AC asynchronous generators (Wenping Cao, March 2012)
...
It is advantageous to use wind turbine generators at
variable speed because of fluctuating nature of wind as it reduces the stress on the blades of
turbine improving the system aerodynamic efficiency and torque transient behaviors (Wenping
Cao, March 2012)
...


a
...
If machine is excited electrically then it follows the concept of shunt wound DC
generators
...
The
rotor consists of conductor windings on armature which is further connected to the split-slip
ring commutator
...
These DC
generators require regular maintenance and are relatively costly because of the presence of
the commutators and brushes (Wenping Cao, March 2012)
...


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b
...
These generators require a continuous source of
reactive power for its excitation in order to continuously generate voltage and supply active
power
...
These induction generators or an
asynchronous generator falls into two categories based on rotor type which are fixed speed
induction generators with squirrel cage rotor (SCIG) and doubly fed induction generators
(DFIG) with wound rotors (Wenping Cao, March 2012)
...
The diagrams of squirrel cage induction generator
and doubly fed induction generators is shown in figure (3-9) and figure (3-10) respectively
...


Figure (3-9): - Cutaway diagram of Squirrel cage induction generator (Wenping Cao, March 2012)

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Image removed due to copyright restriction
...
Power flows in stator in unidirectional ways
however the direction of the power flow in rotor totally depends on the modes of operations
of generator
...
If generator operates
above the synchronous speed or super-synchronously then rotor delivers the power
...
However, these DFIG cannot be considered in a low power standalone wind
turbine system
...
Beside these advantages DFIG has a drawback of reduction of
reliability and increased maintenance requirements due the use of brushes and slip rings
(Zuher Alnasir, 2013)
SCIG has a rotor made of longitudinal conductive bars set into groves and short circuited by
bars
...
They are also smallest in size, lowest in cost and robust in
structure; however, SCIG based wind energy conversion system requires a full capacity
power converters to get maximum power available from wind to achieve full control of

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reactive and active power
...


c
...

Cylindrical rotor has a distributed winding with uniform air gap and salient rotor has
concentrated windings on the pole and non uniform air gap
...
The possibility of eliminating the need of the gearbox which further
reduces the maintenance requirements and increases the system reliability and efficiency are
major advantages of synchronous generators over induction or asynchronous generators
...
The elimination of the gear box saves the money but with this advantage there comes
some drawbacks which are that direct drive generators without gearbox become heavier,
larger in size and more costly due to the need of the larger number of poles required in rotor
...
AC
synchronous wind turbine generators generally fall in two categories which are wound rotor
synchronous generators (WRSG) and permanent-magnet synchronous generator (PMSG)
which are explained next along with their application in wind energy conversion system
...


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Image removed due to copyright restriction
...
Providing an excitation using the help of brushes is a simple method but
requires regular maintenance of the brushes and slip rings whereas in another method less
maintenance is required but this method is more complex and expensive due to the
involvement of power electronics and also needs an auxiliary AC generator
...
The rotor field winding is usually excited with the help of
auxiliary DC source with the help of DC/Dc converters
...
For these purposes
an automatic voltage regulator can be used
...


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Another type of Synchronous generator, permanent magnet synchronous generator, requires
a brushless self excitation for rotor which is produced by the permanent magnets
...
To reduce the cost sometimes the permanent magnets can be integrated
into a cylindrical cast aluminum rotor (Wenping Cao, March 2012)
...
These permanent magnet synchronous generators are rugged,
reliable and simple because of the elimination of brushes, slip rings and commutator
...
However, this
makes impossible to control the required field and the cost the magnets used in these
generators will be higher for larger machines (Wenping Cao, March 2012)
...


Figure (3-12): - Cutaway diagram of permanent magnet synchronous generator (Wenping Cao, March 2012)

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Depending upon the installation of permanent magnets on the rotor, these generators can be
divided into two types first is surface-mounted permanent magnet synchronous generators
and the other one is inset-magnet permanent magnet synchronous generators
...
Owing to this reason and other reasons associated with the efficiency and the power
density of the machine, surface mounted permanent magnet synchronous generators are
preferred for low speed applications of wind turbine (Zuher Alnasir, 2013)
...
These inset magnet permanent magnet synchronous generators
offers high efficiency drive by using the both reluctance and magnetic torque
...
The inset permanent magnet
synchronous generators for large scale wind turbines, provides higher efficiency for different
types of rotor structures
...
To resolve this problem, a light weight structure for permanent
magnet synchronous generators has been proposed in many papers, as a solution for direct
drive wind turbines for large scale applications (Zuher Alnasir, 2013)
...


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Table 1: Advantages and disadvantages of SCIG-WECS and PMSG-WECS

Topology

Indirect-drive SCIG

Direct-drive PMSG

Brushless machine
No windings in rotor
Common properties

Full active and reactive power control
Good control bandwidth

Advantages

Robust operation

Gearless

Low cost

Self excited

Low maintenance

High PF operation

Easier in control

High efficiency
No rotor Copper loss

Disadvantages

Gear box losses and maintenance

Magnet cost

Need for external excitation

PM Demagnetization

Low efficiency

Large size
Complex control
Cogging torque

In addition to advantages and disadvantages of these generators their performance
comparison is given in table 2
...
2
...
Model of generator used in project
After going through all the generators and studying their advantages that they were
providing, permanent magnet synchronous generator was decided to opt for this small scale
wind turbine project
...
Already provided model of permanent magnet synchronous
generator in Matlab Simulink was used
...
The selection of these configurations for permanent magnet synchronous
machine is shown in figure (3-13)
...


Figure (3-14): - Parameters of permanent magnet synchronous machine in Matlab for project

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Chapter 4: Power Electronic Circuits and energy storage system required
for wind energy conversion system
4
...
Power Electronic for project
After generating the electrical energy from the kinetic energy of the wind using the wind turbine
and the generator then there come the need for the power electronics
...
Due to development and
advancement in technology, the performance is steadily increasing and the prices of the devices
are reducing continuously (Zhe Chen, August 2009)
...
Control part of the power electronics looks for steady-state and
dynamic characteristics of closed-loop system
...
In addition to this, electronic part deals
with solid-state devices for the processing of the signals to meet the desired control objectives
(Rashid, 2014)
...
Depending upon the properties
of circuits and applications converter can allow the flow of power in both directions
...
In grid commuted converter systems the
semiconductor device that is used is thyristor with a high power capacity of 6 or 12 or even more
pulses
...
Hence, thyristor converters are mainly used for the very high voltage and power
applications such as traditional HVDC systems (Zhe Chen, August 2009)
...

These types of converters are able to transfer both active and reactive power in both directions
(ac-dc or dc-ac)
...
PWM converters can produce harmonics and interharmonics because of the high
frequency switching, generally in the range of kilohertz
...
In this project for a small scale wind turbine, converters with a control method of
pulse width modulation method were used after the generator section
...
After generating electricity from generator in three phase AC form some
kind of circuit is required which can convert the alternating current generated from generator to
direct current for the storage in battery
...
Beside the rectifier circuit in power electronic circuits, Power
converters mainly either buck or boost converters were used to achieve a required level of DC
voltage at the load side
...
The basic
block diagram of the power electronics used for the project is shown in Figure (4-15)
...


a
...
A rectifier due to its
operation is also known as ac-dc converter
...
Depending upon the type of the input signal applied
to the rectifier it can be categorized into two different types which are single phase and

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three phase
...
Generally in half wave, output is present only for positive cycle of the input
voltage whereas in full wave, output is available for both positive and negative cycle
(Rashid, 2014)
...
A three phase full wave
rectifier is also known as three phase bridge rectifier which is commonly used in high
power applications
...
The circuit
diagram of three phase bridge rectifier is shown in figure (4-16) with pure resistive load
...


Figure (4-16): - Circuit diagram of three phase bridge rectifier (Rashid, 2014)

It is clear from the circuit diagram that the three phase bridge rectifier consists of 6 diodes
which can operate either with transformer or without it, giving six pulse ripples in the
output voltage
...
Each diode conducts for the duration
of 120 degree angle and the conduction sequence in which diodes are turned on is D1 D2, D3 - D2, D3 - D4, D5 - D4 , D5 - D6 and D1 - D6
...
The line voltage is generally represented as a
multiplication of the single phase with

(Rashid, 2014)
...

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Image removed due to copyright restriction
...
The average output voltage at the end rectifier means at load side is shown in
equation (4-8)
...


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At the output of the rectifier some harmonics are also present due to non linear nature of
the diodes leading to the increase in total harmonic distortion of input current
...


b
...
The main
purpose of the DC link capacitor is to maintain a DC voltage with small ripples in output at
steady state and to serve as storage element for energy for supplying real power difference
during the transients between load and source (Jain, 2018)
...
So, a reference value can be set for a DC link voltage (Jain, 2018)
...
DC link capacitor is used to compensate this
difference in the power
...
For the satisfactory operation of the active
filters, the peak value of the reference current must be adjusted in such a way that it
changes with the real power drawn from source proportionally
...
When the DC link voltage is recovered and attains the value same
that of reference voltage then it is supposed that real power supplied by source matches
with the load power consumed again (Jain, 2018)
...

If the value of the DC link voltage is less than reference voltage than this means that the
real power of the supply is not enough to meet the power demands of the load
...
Whereas the larger value of the DC link voltage as compared to reference
voltage tries to decrease the reference source current (Jain, 2018)
...
As the frequency of the signal goes up then
the DC voltage at the input of the capacitor along with the cable inductance causes the
increase in the impedance
...
DC link capacitor is also used to stiffen the DC bus
...
The specification of required ripple voltage on the
DC bus is used to determine the value of the capacitance required (Sylvestre, 2019)
...
Ripples are also introduced in the reference compensating
currents due to voltage ripples
...
Therefore to limit the ripples
in the DC link voltage, a higher value of the capacitor is required which results in
generation of a ripple free reference current
...

For minimizing the ripples in the voltage the selection of the value of the capacitor can be
done while considering the maximum value of the peak to peak switching ripple
the RMS value of the switching ripple

or


...

(4-11)

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Chandanpreet Kaur (2223527)

Thesis Report

c
...
It can be considered as an dc equivalent to an ac transformer with
a turn ratio that varies continuously
...
In case of DC converter both the input and output are dc and they are
able to generate a fixed or variable dc output voltage from a fixed or variable dc voltage
...

DC Converters are used as switching mode regulators to convert the unregulated DC
voltage to regulated one
...
Buck
converter in this project was used to reduce the value of the voltage produced after the
rectifier section (Rashid, 2014)
...
It

consists of one active switch which is controlled by the duty cycle of the pulses provided to
it to turn it on or off, a diode and a filter
...


Image removed due to copyright restriction
...
They operate as a two single pole single through (SPST) bidirectional switch
(Rashid, 2014)
...
That is why the capacitor at the input of
the converter is required and this purpose is served by the DC link capacitor
...

In mode 1 transistor

is switched on at time t = 0
...
The equivalent
circuit diagram of the buck converter in mode 1 is shown in figure (4-19)
...


Figure (4-19): - Equivalent circuit diagram of buck converter for mode 1 (Rashid, 2014)

Mode 2 begins when the transistor

is switched off at time t =

stored in the inductor, the freewheeling diode


...


is turned on again in the next cycle
...


Image removed due to copyright restriction
...
In the figure of waveforms it is
assumed that the current rises and falls linearly
...
In most of the applications the effect of the nonlinear
resistance of the switch is negligible
...


Figure (4-21):- Waveforms of the input and output voltage and current of buck converter for the continuous
flow of inductor current

41

Chandanpreet Kaur (2223527)

4
...


Thesis Report

Energy Storage System

Energy storage units are systems that can receive and store energy from renewable energy
sources or directly from grid
...
For instance electricity can be
converted back to mechanical and heat form very efficiently
...

The main disadvantage of the wind energy is that it is not same all the time and cannot fulfil the
demand of the load all the times
...
There are various technologies for the storage of energy such as Compressed air energy
storage; Hydrogen based energy storage system (also known as fuel cell), Flywheel energy
storage system, super conducting magnetic energy storage system, super capacitors and battery
energy storage system (Luanna Maria Silva de Siqueira, March 2021)
...
To
achieve a desired value of the output voltage required, in power system application multiple cells
are usually connected together
...
The movement of the
ions inside of electrolyte causes electrons to move providing or accumulating electrical energy
upon the electrochemical reaction in cells (Luanna Maria Silva de Siqueira, March 2021)
...
2
...
Types of electrochemical batteries

Generally there are two types of electrochemical batteries
...
They are generally used in
standalone applications where the charging is impossible
...

42

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Thesis Report

Another type is secondary battery also known as researchable batteries
...
This reaction can be reversed by
applying a certain amount of voltage in reverse direction
...
Secondary batteries with a small capacity are generally used
to power up some portable electronic devices such as mobile phones whereas heavy duty
batteries are used in powering electric vehicles and sometimes in high drain applications
such a levelling of load in generation of electricity
...

The rating of the batteries is stated in terms of the average voltage during discharge and the
ampere-hour capacity it can deliver before the voltage drops below the specified limit
...

4
...
2
...
State of charge (SOC) %: The state of the charge (SOC) of a cell is defined as the capacity that is already available
as a function of the rated capacity
...

The cell is known as fully charged when the value of SOC is 100% whereas a SOC of 0%
means that the cell is completely discharged
...
Similarly when the cell starts aging then the maximum value of SOC starts
reducing which means that the 100% SOC for an aged cell would be equivalent to 75% to
80% SOC of new cell (Hamdi Abdi, 2017)
...
The nominal capacity is generally provided by the manufacturer and represents the

maximum amount of charge that can be stored in the battery
...

(4-12)

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Chandanpreet Kaur (2223527)

Thesis Report

b
...
Even if the
cell is not used, due to some internal reactions the cell can still get discharged to a certain
level
...
Self-discharging generally increases
with the increase in temperature (Hamdi Abdi, 2017)
...
Discharge rate: The rate of the discharge of cell is also a vital factor in determining the performance of
the battery
...

d
...
This ratio also depends upon the temperature along with charging and
discharging rates
...
2
...
Control strategies for keeping voltage of battery constant
Generally there are two types of control strategies that can be used to keep the voltage of
the battery constant in a hybrid wind energy conversion system with an application of
battery charging
...
There are also some charging methods
that combine these two control methods
...

a
...
In this algorithm a
DC output voltage of the battery is compared with a reference voltage which is further
used to obtain an error signal
...
The main function of the comparator is to obtain a pulse width
modulation signal which is further used to control the output voltage
...
Generally this controller is also
used to control a duty cycle
...
Eren, 2006)

Image removed due to copyright restriction
...
This charging method also sometimes rises temperature in
the battery which can lead to shorten the life of the battery (S
...


b
...
In this constant current method of charging a
battery, DC output voltage is compared with a reference voltage to get an error signal
...
This error signal then can be fed to
comparator along with a triangular waveform or a controller to obtain a pulse width
modulation signal that is used to control the output current (S
...

This algorithm is more damaging to battery at the end of the cycle
...
The disadvantage of this charging
method is that it may results in large currents which can overcharge the battery,
degrading the life of the battery (S
...

45

Chandanpreet Kaur (2223527)

Thesis Report

Image removed due to copyright restriction
...
Constant Current-constant voltage:This method combines both methods of constant voltage and constant current controls to
keep the battery voltage constant
...

During the second part of the charging cycle, constant voltage charging method is used
...
Both constant current and voltage charging generally
occurs during those parts of cycles when they are least damaging to battery
...
Eren, 2006)
...
Pulse charging:
Pulse charging is another method which is also used to charge the battery
...
Pulses with a larger width are used to increase
the charging time
...

Gassing is avoided in this method because if the current pulses are short than then most
of the current will be used for charging the battery rather than producing gas (S
...


46

Chandanpreet Kaur (2223527)

4
...
4
...
This
model was implementing a generic battery model for most popular battery types
...
The nominal voltage was set to 12 V
in this case and the rated capacity was set to 30 Ah to deliver 360 Watt energy to deliver to
a load
...


Figure (4-24):- Parameters set for battery for wind energy conversion system

The Battery discharge characteristics are displayed in figure (4-25) for the set parameters
of the battery
...


47

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Thesis Report

Figure (4-25):- Nominal current discharge characteristics of Battery

A typical discharge curve consists of three sections
...
Type of the battery determines the width of the
drop
...
Lastly,
the third section represents the total discharge of the battery, when the battery voltage
drops rapidly
...
In this the output of the buck converter was applied to battery which
was further used with reference voltage to obtain an error signal
...


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Chandanpreet Kaur (2223527)

Thesis Report

Chapter 5: Mathematical models of the components required for wind
energy conversion system
5
...


Wind turbine Mathematical model: -

The mathematical relation for the mechanical power extraction from the wind can be expressed
by using the equation (5-13)
...


The tip speed ratio of the wind turbine is given in equation (5-13a)
(5-13a)
In above equation R is the radius of the radius of the blades and

is the angular speed of the

turbine rotor
...

(5-14)
Where
–

and

= 0
...
4,

= 5,

=21 and

=0
...


The torque of the wind turbine can be expressed as shown in equation (5-15) (BOUZID
Mohamed Amine, jan 2014)
(5-15)
The

characteristics of a wind turbine for different values of pitch angle

figure (5-26)
...
1
...
2
...
Following equations were used to model the generator
...
Stator is used to refer all the quantities in rotor
reference frame
...
For example, the inductance measured between phase A
and B (when phase C is left open) is given by equation (5-19)
...


The variation of the phase to phase inductance w
...
t
...


Figure (5-27): - variation of the phase to phase inductance w
...
t
...

(5-20)
For salient pole rotor the phase inductances for both d and q axis are different which is given in
equation (5-21) and (5-22)
...
3
...
As the power provided may be
too high and volatile which can cause a damage to battery, so remedy for this issue is the use of
buck converter, in continuous conduction mode
...
The equivalent circuit of the buck converter is shown in
figure (5-28)
...

The duty cycle of the buck converter, used to control switch of the converter, is modified to
control the output current and output voltage of the buck
...
To get the value of the duty
cycle equation (5-23) was used
...

(5-26)
(5-27)
In above equations C is the value of the capacitor required and

is the output voltage ripple
...
Eren, 2006)
...
4
...
The equations (528) and (5-29) are used to describe the discharge and charge voltage of the battery
...
In constant voltage structure, feedback output voltage of the
battery uses a PI controller for controlling a duty cycle
...
The schematic diagram of the second
order battery-charging system is shown in figure (5-29)
...


Figure (5-29): - Schematic diagram of charging control (Her-Terng Yau, 2012)

The PI controller controls the error signal

(steady-state error signal) to be set at 0, so that the

batter voltage does exceed control or reference voltage , achieving constant voltage
...
The transfer function of
the converter is given in equation (5-30)
...

54

Chandanpreet Kaur (2223527)

Thesis Report

Image removed due to copyright restriction
...
The transfer function is given in equation (5-31)
...


55

Chandanpreet Kaur (2223527)

Thesis Report

Chapter 6: Simulations and Results for wind energy conversion system
This project uses Simulink of MATLAB simulation software to implement a mathematical
model of the overall system
...
Models for wind turbine and generator were
used that were already available in Simulink
...
The generator model used was implementing a
three-phase permanent magnet synchronous generator
...


Image removed due to copyright restriction
...
The Simulink
model of the three phase bridge rectifier, along with generator, used for converting the AC
voltage to DC voltage is given in Figure (6-32)
...
Before applying a controller for the battery, the rectifier was
producing an output of around 56 V so a buck converter was employed after it to step down this
voltage to around 12 V
...


Figure (6-33): - Waveform of variable DC voltage of around 12
...
This same buck converter is also used for controlling the battery voltage
which is connected at the output of the buck converter
...
For implementing controller, a reference
voltage was subtracted from the battery output to obtain a duty cycle
...
The Simulink model of
buck converter section with a battery charger is shown in figure (6-34)
...


Figure (6-35): - Output voltage and SOC of the battery

58

Chandanpreet Kaur (2223527)

Thesis Report

It’s clear from the waveform that the controller was able keep the voltage of the battery constant
to a required level and the SOC curve was also remaining constant indicating the charging phase
of the battery
...
For this a Boost converter was used to provide a
double voltage, with a duty cycle of 50%, than the input voltage to the load
...


Figure (6-36):- Boost converter for applying a double voltage than the input voltage to a constant load

All these values obtained were for the constant speed of the wind which was set to 12 m/sec
...

This model of wind turbine was also tested for some different value of wind speed which was
higher and greater than 12m/s
...
For higher values of the wind such as 15 m/s again the battery voltage was kept constant
with the help of controller used for battery
...

The results for wind speed 8m/s and 15m/s are given in figures (6-37) and (6-38) respectively
...


Figure (6-37): - Result of battery voltage for wind speed of 8m/s and a constant load of 5 ohm supplied with the help
of boost converter

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Chandanpreet Kaur (2223527)

Thesis Report

Figure (6-38): - Result of battery voltage for wind speed of 15m/s and a constant load of 5 ohm supplied with the
help of boost converter

When the value of the constant load of resistance 5 ohm, at the output of the boost converter, was
made variable then the output voltage was also changed
...
Figure (6-39) shows the output voltage of the boost
converter when the load resistance was changed to 10 ohms from 5 ohms
...
89 V
...


Figure (6-39): - change in the output voltage of boost converter with the change in load resistance

62

Chandanpreet Kaur (2223527)

Thesis Report

Chapter7: -Conclusion and Future Work
This thesis has designed the small scale stand alone wind turbine model for application of battery
charging mainly for the remote areas or residential areas and for small businesses where the
connection to grid is not possible
...
A wind turbine with a power of 1
...
The power electronics required for
converting the voltage level to a required value and a nature was also designed properly by
studying the models properly
...
Hence the proposed
model in this thesis is able to provide a constant voltage to the battery with different wind
speeds
...
Hence controller designed for charging a battery with the help of Buck
converter was reliable for charging the battery
...
It can come
from any direction or any side of the wind turbine
...
For capturing such fluctuating
energy some controls can be applied on the Wind turbine section for further work which can be
implemented on this thesis
...
By applying
these controls to the wind turbine, a constant energy even with the fluctuations in the wind can
be provided to the next sections of the wind turbine in this conversion system
...


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Thesis Report

REFERENCE
Anon
...

Vertical
axis
wind
turbine
parts
...
green-mechanic
...
html
Anon
...

sweep
area
of
the
turbine
blades
...
org/2018/10/10/calculate-the-sweep-area-of-turbineblades/
BOUZID Mohamed Amine, M
...
A
...
Z
...
, jan 2014
...
International Journal of Advances in Engineering & Technology, 6(6),
pp
...

Hamdi Abdi, B
...
-i
...
J
...
R
...
E
...
, 2017
...
In: S
...
M
...
G
...

Gharehpetian, ed
...
Iran:
Butterworth-Heinemann, pp
...

Her-Terng Yau, Q
...
L
...
-T
...
, 2012
...
Computers and Mathematics with
Applications, Volume 64, pp
...

Jain, S
...
Control Strategies of Shunt Active Power Filter
...
s
...
:s
...
, pp
...

Luanna Maria Silva de Siqueira, W
...
, March 2021
...
Journal of Energy Storage
...
H
...
S
...
G
...
, 2017
...
Energies,
11 August
...
A
...
T
...
D
...
Overview of batteries State of Charge estimation
methods
...
V
...
, 2018
...
[Online]
Available at: https://circuitdigest
...
Wind energy for sustainable development: Driving factors and future
outlook
...

Rashid, M
...
, 2014
...
4th ed
...

S
...
C
...
D
...
a
...
Y
...
A HIGH PERFORMANCE WIND-ELECTRIC BATTERY
CHARGING SYSTEM
...


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Thesis Report

Sylvestre,
J
...

Inverter
DC
Link
Capacitor
Selection
...
specterengineering
...
, 2010
...
UK: WIT Press
...
X
...
Z
...
, March 2012
...
UK: s
...

Zhe Chen, J
...
G
...
B
...
A Review of the State of the Art of Power Electronics
for Wind Turbines
...
1859-1875
...
K
...
An analytical literature review of stand-alone wind energy
conversion systems from generator viewpoin
...

597-615
...
1 kW
Rated wind speed – 12 m/s
Pitch angle – 0 degree

b) Permanent magnet synchronous generator
Number of phase – 3
Mechanical Input – Torque
Rotor type - Round
Stator resistance – 18
...
0268 H

c) Rectifier specifications
Type – three phase bridge rectifier
Diode resistance – 0
...
8 V
Snubber resistance Rs – 500 ohms
Snubber capacitance Cs - 250e-9 F
Load resistance – 10 Ohms
DC link Capacitor - 470e-6 F

d) Buck converter specifications
Switch Resistance - 1e-3 Ohms
Switch internal diode resistance Rd - 1e-3 ohms
Snubber resistance Rs – 1e5 ohms
Snubber capacitance Cs - inf F
Diode resistance – 1e-3ohms
Diode Forward voltage – 0 V
Diode Snubber resistance Rs – inf
Diode Snubber capacitance Cs – inf
Inductance - 3e-3 H
Capacitance - 30e-6 F
Load Resistance – 100 Ohm

e) Battery specifications
Rated capacity – 30 Ah
Nominal voltage – 12 v
Full charged voltage -13
...
8 V
Diode Snubber resistance Rs – inf
Diode Snubber capacitance Cs – 0
Inductance – 2
...
00011 F
Load Resistance – 5 Ohm

67



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