external_thesis .pdf

APPLICATION OF HYBRID ENERGY STORAGE TO

IMPROVE THE POWER QUALITY OF DOUBLY FED

INDUCTION GENERATOR BASED WIND SYSTEM

A Dissertation

Submitted in partial fulfillment of the requirement for the

award of the degree of

MASTER OF ENGINEERING

In

POWER SYSTEM AND POWER ELECTRONICS

(ELECTRICAL AND ELECTRONICS ENGINEERING)

By

RUBY TRIPATHI 1602-13-766-022

Under the Guidance of

Mr. M. Sreenivasulu

Assistant Professor (Sr. Sl.),

DEPARTMENT

OF

ELECTRICAL AND ELECTRONICS ENGINEERING

VASAVI COLLEGE OF ENGINEERING

(Affiliated to Osmania University)

Ibrahimbagh, Hyderabad – 500031

2014 – 2015

Department of Electrical and Electronics Engineering

Vasavi College of Engineering

Osmania University

CERTIFICATE

This is to certify that the project work entitled “APPLICATION OF HYBRID

ENERGY STORAGE TO IMPROVE THE POWER QUALITY OF DOUBLY

FED INDUCTION GENERATOR BASED WIND SYSTEM” submitted by

RUBY TRIPATHI (1602 – 13 – 766 – 022), a student of Department of Electrical

and Electronics Engineering, Vasavi College of Engineering in partial fulfilment of

the requirements for the award of the degree of Master of Engineering with Power

System and Power Electronics as specialization is a record of the bonafide work

carried out by her during the academic year 2014 – 2015.

Signature of Internal Guide Signature of Head of the Department

Mr. M. Sreenivasulu Mr. K. V. Ramana Murthy

Assistant Professor (Sr. Sl.), Professor & HOD, EEE

Vasavi college of Engineering Vasavi college of Engineering

Hyderabad Hyderabad

DECLARATION

I declare that the work reported in the thesis entitled “APPLICATION OF

HYBRID ENERGY STORAGE TO IMPROVE THE POWER QUALITY OF

DOUBLY FED INDUCTION GENERATOR BASED WIND SYSTEM” is a

record of the work done by me in the Department of Electrical and Electronics

Engineering, Vasavi College of Engineering.

No part of the thesis is copied from books/journals/internet and wherever

referred, the same has been duly acknowledged in the text. The reported data are

based on the project work done entirely by me and not copied from any other source.

Signature of the Student

Name: Ruby Tripathi

Reg. no: 1602 – 13 – 766 – 022

ACKNOWLEDGEMENT

I would like to express my profound gratitude towards Mr. M. Sreenivasulu

Assistant Professor (Sr. Sl.), of the EEE who played a supervisory role to utmost

perfection, enabled me to seek through M.E and for guiding as an internal guide

methodically and meticulously.

I am grateful to Dr. M. Chakravarthy, Professor for his valuable suggestions

and comments during the research work.

I am highly indebt to Mr K.V. Ramana Murthy, Head of the department,

EEE for his energetic support and providing all the necessary support.

I formally thank the Principal Dr. G. V. Ramana Murthy of Vasavi College

of Engineering for providing all the facilities to complete the M. E. programme.

I would also like to thank Electrical and Electronics Engineering staff for

lending us their time to help us to complete our work successfully.

Ruby Tripathi

(1602 – 13 – 766 – 022)

i

ABSTRACT

Over the past 20 years the concern over renewable energy resources is

increasing due to limited conventional resources and increased pollution. In India,

16.8 % of power is contributed by wind energy and with the technological advances

there is a good scope of increasing the power contributed by wind energy. However,

the wind generators when integrated to the grid have adverse effects which lead to the

reduction in power quality. Many researchers have proposed different techniques to

maintain the voltage quality at the PCC by controlling the reactive power. Instead of

controlling the reactive power, an energy storage system can be used to control the

voltage.

The project emphasizes on the application of hybrid energy storage systems to

mitigate the effect of wind speed fluctuations, thereby ensuring smooth power output

as well as improving the power quality at the PCC. To achieve this a control strategy

is designed for managing the demand – generation fluctuations using a hybrid energy

storage system in a wind – dominated remote area power supply system consisting of

a DFIG, a battery / fuel cell storage system , a super capacitor, a dump load and main

loads. Operation of battery / fuel cell storage system is coordinated with a super

capacitor with a view to improving the performance of the battery / fuel cell. In this

model, the battery / fuel cell storage system is connected to the load side of the RAPS

system, whereas the super capacitor is connected to the dc bus of the back – to – back

converter of the DFIG. The models are simulated in Matlab / Simulink environment.

ii

TABLE OF CONTENT

ABSTRACT .................................................................................................................. I

LIST OF FIGURES .................................................................................................... V

LIST OF TABLES ................................................................................................... VII

GLOSSARY OF ACRONYM ............................................................................... VIII

LIST OF ABBREVIATIONS .................................................................................... X

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

INTRODUCTION........................................................................................................ 1

1.1 Introduction to Renewable Energy Resources. .................................................... 1

1.2 Introduction to Wind Energy................................................................................ 2

1.3 Types of Wind Turbine Generators ...................................................................... 4

1.4 Introduction to Storage System ............................................................................ 4

1.4.1 Introduction to Battery................................................................................... 4

1.4.2 Introduction to Super Capacitor .................................................................... 5

1.4.3 Introduction to Fuel cell ................................................................................ 6

1.4.4 Hybrid storage system ................................................................................... 6

1.5 Overveiw .............................................................................................................. 7

1.6 Outline of the Thesis ............................................................................................ 7

CHAPTER 2 ................................................................................................................. 9

LITERATURE SURVEY ............................................................................................ 9

2.1 Electrical Energy and Importance of DFIG ......................................................... 9

2.2 Controlling Schemes and Storage Systems .......................................................... 9

2.3 Chapter Summary ............................................................................................... 10

CHAPTER 3 ............................................................................................................... 11

DFIG OPERATION AND CONTROLLING ......................................................... 11

3.1 Operation of the DFIG ....................................................................................... 11

3.2 Rotor Side Converter Control ............................................................................ 13

3.3 Line Side Converter Control .............................................................................. 15

3.4 Pitch Angle Control ............................................................................................ 16

3.5 Chapter Summary ............................................................................................... 17

iii

CHAPTER 4 ............................................................................................................... 18

PROPOSED MODEL AND ITS DETAILED STUDY .......................................... 18

4.1 Existing Model of RAPS System ....................................................................... 18

4.2 Proposed Model of RAPS System ..................................................................... 19

4.3 A Coordinated Control Approach for Hybrid Energy Storage. ......................... 20

4.4 The Power Management Algorithm. .................................................................. 22

4.5 Battery/Fuel cell Storage Function. .................................................................... 24

4.5.1 Estimation of Battery ................................................................................... 25

4.5.2 Estimation of Fuel Cell ................................................................................ 25

4.6 Super Capacitor and Dump Load. ...................................................................... 26

4.6.1 Estimation of Supercapacitor....................................................................... 28

4.6.2 Dump Load Controller ................................................................................. 29

4.7 Chapter Summary ............................................................................................... 30

CHAPTER 5 ............................................................................................................... 31

SIMULATION MODEL AND RESULTS .............................................................. 31

5.1 Simulation Model with Battery and Super Capacitor as Hybrid Storage System

.................................................................................................................................. 31

5.1.1 RSC and LSC Design. ................................................................................. 33

5.1.2 Battery/fuel cell, Supercapacitor and Dump Load Contol .......................... 35

5.2 Simulation Model with fuel cell and Super Capacitor as Hybrid Energy Storage

.................................................................................................................................. 35

5.3 Performance of the Hybrid Energy Storage System Based DFIG System. ....... 37

5.3.1 Battery and super capacitor results .............................................................. 37

5.3.2 Fuel cell and super capacitor results ............................................................ 43

5.3.2.1 Results with Constant Load .................................................................. 43

5.3.2.2 Results with Variable Load ................................................................... 48

5.4 Comparison of Battery and Fuel cell as Storage Systems. ................................. 54

5.5 Chapter Summary ............................................................................................... 54

CHAPTER 6 ............................................................................................................... 56

CONCLUSION AND FUTURE SCOPE ................................................................. 56

6.1 Conclusion .......................................................................................................... 56

6.2 Future Scope ....................................................................................................... 56

iv

REFERENCES ........................................................................................................... 58

APPENDIX ................................................................................................................. 60

A.1 Parameters Associated with DFIG Based RAPS System. ................................. 60

v

LIST OF FIGURES

Figure 1.1: Renewable energy installed capacity .......................................................... 1

Figure 1.2: India’s wind power installed capacity ......................................................... 3

Figure 1.3: Types of wind turbines ................................................................................ 4

Figure 1.4: Different storage systems ............................................................................ 7

Figure 1.5: Outline of Thesis ......................................................................................... 8

Figure 3.1: DFIG based wind turbine generator system .............................................. 11

Figure 3.2: Super – synchronous mode of operation ................................................... 12

Figure 3.3: Sub – synchronous mode of operation ...................................................... 12

Figure 3.4: RSC control scheme .................................................................................. 15

Figure 3.5: Filter model associated with LSC ............................................................. 15

Figure 3.6: LSC control scheme .................................................................................. 16

Figure 3.7: Pitch angle controlling ............................................................................... 17

Figure 4.1: Existing model of DFIG based RAPS system ........................................... 18

Figure 4.2: Proposed model of DFIG based RAPS system ......................................... 19

Figure 4.3: A Coordinated control approach for hybrid energy storage based RAPS

system ................................................................................................................... 21

Figure 4.4: Estimation of reference power for battery/fuel cell and super capacitor .. 22

Figure 4.5: Operating frequency ranges for storage system ........................................ 23

Figure 4.6: Types of super capacitor............................................................................ 24

Figure 4.7: Inverter control .......................................................................................... 26

Figure 4.8: Buck – Boost converter ............................................................................. 26

Figure 4.9: Super capacitor controlling strategy. ......................................................... 28

Figure 4.10: Dump load control strategy. .................................................................... 29

Figure 5.1: Simulation circuit with battery and super capacitor .................................. 32

Figure 5.2: RSC controlling circuit .............................................................................. 33

Figure 5.3: LSC controlling circuit .............................................................................. 34

Figure 5.4: Simulation model with fuel cell and super capacitor ................................ 36

Figure 5.5: Torque and Speed of DFIG ....................................................................... 37

Figure 5.6: Wind speed (Battery)................................................................................. 38

Figure 5.7: Voltage on load side (Battery) ................................................................... 38

Figure 5.8: Frequency on load side (Battery) .............................................................. 39

vi

Figure 5.9: DC link Voltage (Battery) ......................................................................... 39

Figure 5.10: Load Demand (Battery) ........................................................................... 40

Figure 5.11: Wind Power (Battery) ............................................................................. 40

Figure 5.12: Hybrid energy storage power .................................................................. 41

Figure 5.13: Dump Load Power (Battery) ................................................................... 41

Figure 5.14: Battery current ......................................................................................... 42

Figure 5.15: Hybrid Energy storage current ................................................................ 42

Figure 5.16: FFT analysis of the battery system .......................................................... 43

Figure 5.17: FFT analysis of the Super capacitor ........................................................ 43

Figure 5.18: Wind Speed ( Fuel cell) ........................................................................... 44

Figure 5.19: Voltage on load side (Fuel cell) .............................................................. 44

Figure 5.20: Frequency on load (Fuel cell) .................................................................. 45

Figure 5.21: DC link Voltage (Fuel cell) ..................................................................... 45

Figure 5.22: Load Demand (Fuel cell) ......................................................................... 46

Figure 5.23: Wind Power (Fuel cell) ........................................................................... 46

Figure 5.24: Hybrid energy storage power .................................................................. 47

Figure 5.25: Dump Load Power (Fuel cell) ................................................................. 47

Figure 5.26: Hybrid Energy storage current ................................................................ 48

Figure 5.27: Wind Speed (Fuel cell) ............................................................................ 48

Figure 5.28: Voltage on Load Side (Fuel cell) ............................................................ 49

Figure 5.29: Frequency on Load Side (Fuel cell) ........................................................ 49

Figure 5.30: DC Link Voltage (Fuel cell) .................................................................... 50

Figure 5.31: Load Demand (Fuel cell) ......................................................................... 51

Figure 5.32: Wind Power (Fuel cell) ........................................................................... 51

Figure 5.33: Hybrid Energy Storage Power ................................................................. 52

Figure 5.34: Dump Load Power ( Fuel cell) ................................................................ 52

Figure 5.35: Fuel Cell Current ..................................................................................... 53

Figure 5.36: Hybrid Energy Storage Current ............................................................... 53

vii

LIST OF TABLES

Table 1.1: Available Supercapacitors in Market............................................................ 6

Table A.1: Parameters .................................................................................................. 60

viii

GLOSSARY OF ACRONYM

ρ Air density in Kgm-3

A Area swept by the rotor blades in m2

ib Battery current

ifc Fuel cell current

Pb Battery power output

Vb Battery voltage

Csup Capacitance of super capacitor in F

(Vw)cut – in Cut – in wind speed in ms-1

(Vw)cut – out Cut – out wind speed in ms-1

D Damping Constant

Vdc DC bus voltage

Pd Dump load power

Vds, Vqs d and q axes voltage on load side

Vdr, Vqr d and q axes voltage on rotor side of the DFIG

Фds, Фqs d and q axes stator flux components of DFIG

Фds, Фqs d and q axes rotor flux components of DFIG

Te Electrical torque of wind turbine generator

F Faraday constant in Ckmol-1

ŋF Faraday efficiency

Lf Filter inductance

∆f Frequency deviation

fs Frequency on load side

σ Leakage factor of DFIG

PL Load demand

Plf, Phf Low and high frequency power component

Lm Magnetising inductance of the DFIG

Pm Mechanical power output of the wind turbine

Qmag No – load reactive power output from DFIG

(Te)opt Optimum torque of the wind turbine generator

(Pw)opt Optimum wind power output

∆p power deviation

ix

PDFIG Power output of the DFIG

kp,ki Proportional and integral gains of a PI controller

Фrated Rated flux of the DFIG

Qs Reactive power of the stator of the DFIG

QDFIG Reactive power output from DFIG

Φr Rotor Flux of the DFIG

Rr Rotor resistance of the DFIG

Lr Rotor inductance of the DFIG

Pr Rotor power of the DFIG

ωr Rotor speed of the wind turbine generator

S Slip of the DFIG

Фs stator Flux of the DFIG

Rs Stator resistance of the DFIG

Ls Stator inductance of the DFIG

Psc Super capacitor power output

Pfc Fuel cell power output

ωs Synchronous speed

Vsc Voltage across the super capacitor

Vs Voltage on load side

Pw Wind power output

Vw Wind speed in ms-1

x

LIST OF ABBREVIATIONS

DFIG Doubly fed induction generator

SEIG Self excited induction generator

PMSG Permanent magnet synchronous generator

MW Mega Watt

WECS Wind Energy Conversion System

RAPS Remote Area Power Supply

RSC Rotor Side Converter

LSC Line Side Converter

PCC Point of Common Coupling

EMA Energy management algorithm

PLL Phase Locked Loop

DOD Depth of Discharge

PWM Pulse Width Modulation

SOC State of Charge

BESS Battery Energy Storage System

FESS Fuel cell Energy Storage System

HESS Hybrid Energy Storage System

PEMFC Proton Exchange Membrane fuel cells

1

CHAPTER 1

INTRODUCTION

Electricity is identified as one key commodity which can be used as a

medium for economic growth in rural and regional areas. According to ministry of

new and renewable energy, country's present installed power generation capacity has

more than doubled to 2,54,600 MW in the past 10 years [1]. Renewable energy

contributes to nearly 34351.39 MW to the total generating capacity and in which wind

energy contributes 21923 MW as shown in Fig.1.1. Even though we have 2,34,600

MW of installed capacity, India faces an outage of more than 30000 MW due to

increase in demand. This shortage can be reduced by use of renewable energy, since

renewable energy is reliable, abundant and will cost efficient once the technology

improve.

In remote areas such as island where supplying power is uneconomical

through grid, in those it will quite efficient if small generation systems are developed

and power is supplied though it. Thus developing a DFIG based RAPS system.

Figure 1.1: Renewable energy installed capacity

1.1 INTRODUCTION TO RENEWABLE ENERGY RESOURCES.

The electrical industry has begun to improve more and more in recent

years. Relevant issues such as global warming, energy cost, power market, and

Wind Power =

21923 MW

Solar Power = 2180

MW

Small Hydro Power

= 3762.15 MW

Bio-Mass Power

= 1284.6 MW

Biogass Power =

2912.88 MW

2

increasing energy demand have affected power industry growth. Over the past years,

development of smaller distributed energy sources closer to loads such as Remote

Area Power Supply (RAPS) system has increased. Thus, renewable energy sources

such as wind, solar, biomass, and geothermal are given more importance.

Renewable energy systems offer several advantages over conventional energy

sources such as natural gas or coal. First, renewable energy systems are clean

sources of energy found in most regions, and they do not emit greenhouse gases.

Renewable energy sources are also abundant and free. Although the initial capital

cost for most renewable energy sources is greater than natural gas or coal power

plants, renewable may be more cost – effective for long term as compared to

conventional sources because of lower operating and maintenance costs. However, the

renewable resources have several disadvantages. Primary disadvantage is that they

are mostly available in remote areas at great distances from large loads.

Among all renewable energy options, wind power has gained the importance

as one of the most widespread renewable energy generation technologies. In this

thesis, wind energy is emphasized because it can be used to generate electricity in

remote areas where grid is neither available nor electricity is economical to transfer

via grid.

1.2 INTRODUCTION TO WIND ENERGY.

Wind energy generation began in the 1980s, when wind turbines with only a

few tens of kW rating were connected to power grids without much control. Due to

variations in wind speed, it became difficult in generating power and connecting it

directly to the grid. Furthermore, this system had no control on active and reactive

power transfer. Today, great improvements has been made in wind energy generation

and power electronics devices are used to control and transfer active and reactive

power between wind turbines and grid.

At present wind energy has the greatest share among all other renewable

energy resources. The capacity of wind electrical generation has increased more than

two times and the cost has decreased by one – sixth due to technological

advancements.

3

According to the World Wind Energy Report 2014[1], all wind turbines

installed globally by the end of year 2014 contribute potentially 430 Terawatthours

to the worldwide electricity supply which supply 2.5 % of the global electricity

demand per year. India’s wind power installed capacity by the end of March 2015 is

shown in Fig.1.2 which has increased significantly from 1666 MW to 21923 MW.

Figure 1.2: India’s wind power installed capacity

Although wind power generation schemes are seen to offer great

opportunities in supplying power, they encompass many challenges in standalone

mode of operation. Therefore, wind energy based power generating schemes are

always equipped with the power electronic arrangements along with their respective

control techniques.

The use of power electronic interfaces in hybrid RAPS systems creates many

challenges. Firstly, power electronic interfaces lower the overall system inertia which

will adversely affect the voltage and frequency at the customer end. Secondly, the

costs associated with power electronic systems are considerably high. Therefore, it

is important to select the best hybrid RAPS configuration without compromising on

the power quality and reliability [3]. In addition to the above, other challenges

associated with RAPS systems are: (a) coordination of the functions among all

components, and (b) optimising the financial returns. Selection of suitable energy

sources to form a hybrid RAPS system depends entirely on the availability of

resources within the locality. Usually, variable speed wind turbine generator

technologies are preferred in a standalone power system, as they are able to provide

better voltage and frequency regulation when compared to constant speed

generators such as induction generators.

4

1.3 TYPES OF WIND TURBINE GENERATORS

There are basically three types of wind generators namely self excited

induction generator (SEIG), doubly fed induction generator (DFIG) and permanent

magnet synchronous generator (PMSG). All the 3 types of generator are shown in

Fig.1.3. In this project, DFIG is used. In DFIG power is fed to both stator and rotor

[3]. The primary advantage of DFIG when compared to other generators is that when

used in wind turbines they allow the amplitude and frequency of their output voltage

to be maintained at a constant value, independent of wind speed.

Figure 1.3: Types of wind turbines

1.4 INTRODUCTION TO STORAGE SYSTEM

In order to maintain smooth power flow with constant voltage and frequency,

RAPS system should be integrated with energy storage system. Ideal energy storage

in a standalone wind energy conversion system should be able to provide both high

energy and power capacities to handle situations such as wind gusts and load step

changes, which may exist for seconds or minutes or even longer. At present, various

types of storage technologies are available to fulfill either power or energy

requirements of a RAPS system. Widely used energy storage technologies that

currently employ in wind farms are batteries, super capacitors, flywheels, compressed

– air energy storage, hydro – pumped storage, superconducting magnetic energy

storage, fuel cells, etc. [10], [11].

1.4.1 INTRODUCTION TO BATTERY

Battery storage was used in the early days of direct – current electric power

networks, and is appearing again. Battery systems connected to large solid – state

converters have been used to stabilize power distribution networks. For example

SEIG PMSG

DFIG

5

many "off – the – grid" domestic systems rely on battery storage, but storing large

amounts of electricity in batteries or by other electrical means has not yet been put to

general use.

Batteries are generally expensive, have high maintenance, and have limited

life spans. But one and only possible technology for large – scale storage are batteries.

Nickel – metal – hyderite batteries are not much expensive to implement on a large

scale and have been used for grid storage in Japan and in the United States. Battery

storage has relatively high efficiency, as high as 90% or better.

Rechargeable flow batteries can be used as a rapid – response storage medium.

These storage systems are designed to smooth the transient fluctuations in wind

energy supply.

The advantages of battery are:

They can operate over wide temperature range

They are available in various size.

Depending upon the application, it is possible to charge battery for

long periods of time without self – discharge.

1.4.2 INTRODUCTION TO SUPER CAPACITOR

Supercapacitor is a double layer capacitor in which the energy is stored by

charge transfer at the boundary between electrode and electrolyte. The amount of

stored energy is function of the available electrode and electrolyte surface, the size of

the ions, and the level of the electrolyte decomposition voltage.

Usually supercapacitors are divided into two types: double – layer capacitors

and electrochemical capacitors.

The most important parameters of a super capacitor include the

capacitance(C), ESR and EPR (which is also called leakage resistance). Some of

supercapacitors available in market are shown in Table.1.1.

6

Table 1.1: Available Supercapacitors in Market.

S.No Manufacturer Specifications of Supercapacitors

1 Power Star China Make

(single Unit)

50 F/2.7V, 300F/2.7V, 600F/2.7 V, ESR less than

1mΩ.

2 Panasonic Make (Single

Unit) 0.022-70F, 2.1-5.5V, ESR 200 mΩ-350 Ω

3 Maxwell Make

(Module)

63F/125V, 150A ESR 18 mΩ 94F/75 V, 50 A,

ESR 15 mΩ

4 Vinatech Make 10-600F/2.3V, ESR 400 -20 mΩ, 3-350F/2.7,

ESR 90-8 mΩ

5 Nesscap Make (module) 15V/33F, ESR 27 mΩ 340V/ 51F, ESR 19 mΩ

1.4.3 INTRODUCTION TO FUEL CELL

The chemical energy stored in hydrogen and several hydrocarbon fuels is

significantly higher than that found in common battery materials. This leads to the

development of fuel cells for a variety of applications. Fuel cells are an ideal primary

energy conversion device for remote site locations and find application where an

assured electrical supply is required for power generation, remote and uninterruptible

power. The PEMFC Proton exchange Membrane fuel cells are considered to have the

highest energy density of all the fuel cells, and due to the nature of the reaction have

the quickest start up time (less than 1 sec) so they have been favoured for applications

such as vehicles, portable power and backup power applications.

1.4.4 HYBRID STORAGE SYSTEM

In the proposed system, HESS is used. Hybrid energy storage system is a

system which consists of a battery / fuel cell and a super capacitor which are

comparativel good when compared other storing device as shown in Fig.1.4. Among

all energy storage systems, batteries are seen to have one of the highest energy density

levels but not as good as fuel cell i.e., it is able to store for longer periods, whereas the

supercapacitors seem to have the highest power density i.e., they are able to handle

transients that occur over short period of time. At present, battery storage systems are

widely employed in most real– life RAPS applications [12] but fuel cell are taking

over them in coming years.To improve the performance of the battery / fuel cell

energy storage systems, a supercapacitor can be incorporated to perform a hybrid

7

operation and the combined energy storage system is able to satisfy both power and

energy requirements of the RAPS system [14], [15]. A power management algorithm

is designed in such a way that the supercapacitor should be able to absorb the ripple

component of demand – generation mismatch.

Figure 1.4: Different storage systems

1.5 OVERVEIW

In this thesis, a simulation model of DFIG based wind dominated RAPS

system is developed. The system is designed in order to maintain the load side

voltage and frequency within acceptable limits during over – generation and under –

generation. To achive this main objective, it is important to manage the active and

reactive power contribution of the components in RAPS system. In this regard,

control coordinated strategies are developed and implemented among the components

present within the RAPS system. In addition, individaul control is developed based on

an appropriate coordinated control approach with a view to regulate the magnitude of

the voltage and freqency on the load side. In this thesis, RAPS systems consisting of

battery / fuel cell storage, super capacitor and dump load are expalined briefly along

with simulation models. A comparison of battery versus fuel cell energy storage

system is done.

1.6 OUTLINE OF THE THESIS

A brief description of the contents of the chapter is given below:

A brief introduction about the project is discussed in chapter 1.

Chapter 2 is a literature survey providing detailed information about the

previous works done in this field.

8

In chapter 3, the operating and controlling methods developed for DFIG are

discussed in detail. RSC and LSC controlling techniques are also discussed in

detailed.

In chapter 4, importance of integrating energy storage for wind turbine ,

necessity for supercapacitor for improving the life span of battery and dump load

controlling are discussed in detail.

Chapter 5 gives a detailed study of two simulation models, one with battery

and super capacitor as hybrid storage system and other with fuel cell and super

capacitor as hybrid storage system. Results are discussed in detailed with the

variations in wind and load for both the systems and a comparative study is done.

Finally, chapter 6 summarises the major outcomes of the work presented in

thesis and makes suggestions for future scope.

Figure 1.5: Outline of Thesis

Chapter 1

Introduction

Chapter 2

Literature survey

Chapter 3

DFIG operation and controlling

Chapter 4

Proposed model

Chapter 5

Simulation models and Results

Chapter 6

Conclusion and Future scope

9

CHAPTER 2

LITERATURE SURVEY

During the research work, various papers and journals have been reviewed and their

brief overview is presented.

2.1 ELECTRICAL ENERGY AND IMPORTANCE OF DFIG

Paul Cook et al, [2] explains the importance of providing electricity in rural areas. In

this paper author explains about how the electricity leads to the development of rural

area. In this paper author gives importance to both grid and off – grid development

which can also help in generating in – come for rural areas.

S. Muller, M.Deicke, & Rik W.De Doncker et al, [3] explains the importance of

DFIG and its working. The authors’ gives more important to widely used variable –

speed wind – generator concepts are doubly – fed induction generators (DFIG). The

paper explains the working of DFIG and lists out its advantages over other turbine

generators.

Dr John Fletcher and Jin Yang et al, [5] proposed the controlling of DFIG by

employing RSC and LSC converters. The paper explains about the functioning of

RSC and LSC. Authors also explain about the back – to – back arrangement of the

converters. Paper also explains the importance of DC link capacitor which acts as a

link between converters.

2.2 CONTROLLING SCHEMES AND STORAGE SYSTEMS

Ajay Kushwaha, Inderpreet Singh et al, [6] paper explains about the different control

schemes mainly of doubly fed induction generator (DFIG) wind turbine. This paper

gives the proper explanation of control schemes along with their limitations. Working

of DFIG wing turbine not only depends on the type of generator but also on the

control strategies used. Vector control (VC) scheme is used for controlling the DFIG

D. Santos – Martin, S. Arnaltes, and J. L. R. Amenedo et al, [8] paper explains about

the controlling of reactive power output of DFIG based wind turbines.

M. Beaudin, H. Zareipour, A. Schellenberglabe, and W. Rosehart et al, [10] explains

about the importance of storage system and their advantages in improving the power

10

quality. Author explains about the battery technology, flywheel technology and

capacitors as storing devices for improving the power quality. The authors also

address about the cost of each devices.

Kuldeep Sahay, Bharti Dwivedi et al, [11] explains about the power quality problem

that affects the operating equipments for end user. RAPS system associated with

serious power qualities issues. The paper focuses on importance of the use of energy

storage devices to improve power quality.

Martin Winter et al, [15] briefly explain about the battery, fuel cell and super

capacitor working and construction. Author also gives a brief description of

advantages and disadvantages of each storing system.

N. Mendis at el, [4] describes the importance of battery storage for maintaining the

power balance between load and source and improving voltage at PCC. The use of

super capacitor for improving battery lifetime is also explained.

In the proposed model battery energy storage system is replaced with Fuel cell Energy

storage system and a comparative analysis is made.

2.3 CHAPTER SUMMARY

This chapter summarizes a brief description of different kinds of work done if

the field of DFIG and RAPS system. The different types of controlling approaches

adopted by different authors for controlling DFIG are explained. An overview of

energy storing systems available in the market is discussed.

11

CHAPTER 3

DFIG OPERATION AND CONTROLLING

This chapter presents the relevant study of the DFIG operation and controlling.

Section 3.1 gives a complete study of advantages and operation of DFIG. Section 3.2

explains about RSC controlling. In section 3.3, Controlling of LSC is explained with

necessary contolling scheme. Finally, in section 3.4 Pitch angle controlling is

explained.

3.1 OPERATION OF THE DFIG

In this thesis, DFIG is given much importance because in DFIG power is fed

to both stator and rotor. The primary advantage of DFIG when compared to other

generators is that, when they are used in wind turbines, they allow the amplitude and

frequency of their output voltage to be maintained at a constant value, no matter the

speed of wind blowing on the wind turbine rotor. A typical configuration of a DFIG

based wind turbine generator system is shown in Fig.3.1, the operation of which can

be categorised into two modes: (a) super – synchronous and (b) sub – synchronous.

The difference between operations of these two modes can be determined from the

rotor speedωr , compared to the synchronous speedωs , and the direction of power

flowing through the back – to – back converter.

Figure 3.1: DFIG based wind turbine generator system

12

In the super – synchronous mode, the rotor speed of the DFIG is kept above

synchronous speed leading to a negative slip s < 0, as evident from Eq. (3.1). During

the super – synchronous mode, the generated wind power passes to the load through

the stator, as well as through the rotor, of the DFIG which is given by Eq.(3.2) and

(3.3) respectively (i.e., Pr > 0) as shown in Fig.3.2.

Figure 3.2: Super – synchronous mode of operation

In contrast, during the sub – synchronous mode of operation, the rotor speed is

kept below the synchronous speed. The generated wind power is supplied to the load

by the stator while slip power is absorbed through the rotor (i.e., Pr < 0) as shown in

Fig.3.3.

Figure 3.3: Sub – synchronous mode of operation

The total mechanical power input to the DFIG from the wind turbine generator

is given in Eq. (3.4) [5], [6].

13

s =ωs −ωr

ωs (3.1)

Ps =Pm

(1−s) (3.2)

Pr = −sPs (3.3)

Pm = Ps + Pr (3.4)

Operation of the DFIG is mainly determined by control aspects associated

with back –to – back converter system, namely: Rotor Side Converter (RSC) and Line

Side Converter (LSC) as shown in Fig.3.1. Based on the specific functions expected

from the RSC and LSC, different control strategies should be implemented. As an

example, during the grid – connected operation, the RSC can be used for

torque/speed control, together with terminal voltage or power factor control.

Contrarily, in standalone operation the RSC can only be used to control the load

side voltage and frequency in the absence of other types of generating sources.

3.2 ROTOR SIDE CONVERTER CONTROL

As shown in Fig.3.4, the RSC controller consists of inner – loops which

have fast field oriented current control and the slow outer – loops that generate the

reference currents for the inner loops. The designing work for the RSC is discussed

by taking into consideration the main objectives (i.e. voltage and frequency

regulation) as stated in Chapter 1. The voltage controller of the DFIG is developed

using a reactive power based control approach. In this regard, the total stator

reactive power output Qs, of DFIG given in Eq.(3.5) [3].

Qs =3

2 −

Vs2

ωLs+ Vs

Lm

Lsidr (3.5)

The rotor d – axis current idr, consists of two components, namely:

magnetising current, idrmag, which is mainly used for magnetisation purpose of the

DFIG and idrgen which is used to satisfy the reactive power requirements of the

loads. The corresponding reactive power components of these two currents,

namely: Qmag and Qgen are given by Eq.(3.6) and Eq.(3.7) respectively.

Qmag =3

2 −

Vs2

ωLs+ Vs

Lm

Lsidrmag (3.6)

Qgen =3

2Vs

Lm

Lsidrgen (3.7)

14

The no – load reactive power can be compensated by imposing the condition

given by Eq.(3.8). In addition, the reference current of idrgen can be established by

considering the voltage error which is compensated through a PI controller as in

Eq.(3.9). Therefore, the reference d – axis component of the current which is used to

satisfy the magnitude of the stator voltage can be given as in Eq.(3.10).

idrmag =Vs

ωLm (3.8)

(idrgen ω)ref = Kp + Ki ((Vs)ref − Vs ) (3.9)

(idr )ref = (idrgen )ref + idrmag (3.10)

where, kp and ki are proportional and integral gains of the PI controller respectively.

The stator flux orientation scheme for the machine is ensured by setting the

q – axis component of the stator flux to zero. Mathematically this condition can be

given as in Eq.(3.11) and is regarded as a criterion which needs to be followed by the

DFIG in order to regulate the frequency at the stator or load side.

iqr = −Ls

Lmiqs (3.11)

Therefore, q – axis component of the rotor current given in Eq.(3.11) is

considered as the reference q – axis component of the rotor current which is used to

achieve frequency regulation. In addition, a virtual phase lock loop (PLL) is used to

define the reference frequency for the entire control scheme of the RSC as shown in

Fig.3.5.

RSC control algorithm is implemented by mainly considering the conditions

given in E q . (3.10) , which are used to define the d and q axes reference currents

respectively for the inner – loop controllers as shown in Fig.3.4. These reference

currents are compared with the actual rotor currents, idr and iqr and the error signals

are then compensated using the PI controllers to generate the switching signals for

the RSC. The entire control structure associated with RSC is shown in Fig.3 . 4 .

15

Figure 3.4: RSC control scheme

3.3 LINE SIDE CONVERTER CONTROL

The LSC is used to control the DC bus voltage of the back – to – back

converter system and to supply any reactive power to the loads if needed. In this

regard, the L – R filter model shown in Fig.3.5 is used to develop the model of the

controllers for LSC.

Figure 3.5: Filter model associated with LSC

The control scheme of LSC consists of a fast inner current control loop which

controls the current through the filter circuit given in Fig.3.5. The outer slower

control loops are used to regulate the DC bus voltage of the back – to – back

converter and control reactive power supply through LSC.

16

PLSC =3

2Vds ids (3.12)

QLSC =3

2Vds iqs (3.13)

With reference to Eq.(3.12) and Eq.(3.13), it is evident that the d and q

axes components of currents through filter can be used to regulate the DC link

voltage and reactive power supply to the loads respectively. There is a possibility of

supplying reactive power through LSC to a static synchronous compensator

(STATCOM). In the present work, the reactive power reference Qref is set at zero.

The corresponding control scheme implemented for LSC is shown in Fig.3.6.

Figure 3.6: LSC control scheme

3.4 PITCH ANGLE CONTROL

A pitch angle regulator can be regarded as a mechanical control scheme that

can be utilised to limit: (a) power output and (b) speed of a wind turbine

generator. Although variable speed wind turbine generators allow operation under

different speeds, there is a maximum safe operating speed limit for each type of

generator (e.g. the maximum speed of a DFIG based wind turbine is limited to

1.2 or 1.3 pu of its rated speed). If the wind turbine generator exceeds the

maximum speed limit, pitch regulation can be employed in a manner that the power

output of the wind turbine generator is regulated by adjusting the angle of the

turbine blades to compensate for wind speed variations.

17

Figure 3.7: Pitch angle controlling

There are various pitch regulation schemes employing for wind turbine

generators. The adopted pitch regulation control scheme is shown in Fig.3.8. The

pitch controller computes pitch angle β by comparing the difference between the

maximum speed (ωr)max, and operating speed ωr.

However, the pitch angle controller is a mechanically controlled mechanism

which cannot be effectively utilised to limit the power output of the wind turbine

generator quickly due to slower mechanical dynamics. As an alternative solution,

a dump load can be employed into a RAPS system.

3.5 CHAPTER SUMMARY

This chapter explained about the DFIG operation and its controlling. Rotor

side converter and Line side converter operation was also explained along with their

controlling schemes. The controlling implemented is flux oriented vector control and

pitch angle controlling is also studied.

18

CHAPTER 4

PROPOSED MODEL AND ITS DETAILED STUDY

This chapter presents the relevant study of the proposed model. Section 4.1

gives a complete study of existing model of DFIG based wind dominated remote area

power supply (RAPS) system using hybrid (battery and supercapacitor) energy

storage. In section 4.2, proposed model that is developed is discussed in detail. In

section 4.3, a coordinated control approach for hybrid enegy storage based RAPS

system is discussed. Section 4.4 describes the power management algorithm for

hybrid energy storage system. Section 4.5 describes fuel cell storage function. Finally

in section 4.5, function of super capacitor and dump load is explained along with

controlling schemes.

4.1 EXISTING MODEL OF RAPS SYSTEM

The existing model of the DFIG based RAPS system consisting of the

hybrid (battery and super capacitor) energy storage and dump load with main loads is

shown in Fig.4 . 1 . The battery storage is connected to the load side using an inverter

whereas the super capacitor is interfaced to the DC bus of the back – to – back

converter system by means of a bi –directional buck boost converter. In the present

model battery system was used to charge and discharge according to the variations in

load.

Figure 4.1: Existing model of DFIG based RAPS system

19

The battery that is used is NiMH, which is capable of delivering high

discharge current, but repeated discharges of high load currents reduces the battery’s

life cycle. These limitations of batteries lead to its replacement with fuel cell.

4.2 PROPOSED MODEL OF RAPS SYSTEM

The proposed model with hybrid (Fuel cell and super capacitor) energy storage

and dump load with main loads is shown in Fig.4 . 2 . The fuel cell storage is

connected to the load side using an inverter whereas the super capacitor is interfaced

to the DC bus of the back – to – back converter system by means of a bi –directional

buck boost converter.

The operation of the entire RAPS system is designed according to the

coordinated control approach given in Fig.4 . 3 .T he energy management algorithm

is developed for the hybrid energy storage system based on the operating frequency

of battery/fuel cell storage and super capacitor as it is shown in Fig.4.4, which is

taken as the basis for the development of the controllers associated with the power

electronic interfaces.

The control strategies that are used to control the back – to – back converter

system of the DFIG are the same as which were illustrated in Section 3.2 and 3.3 of

Chapter 3. The control strategies associated with the battery/fuel cell storage system,

super capacitor and dump load are explained in the following sections.

Figure 4.2: Proposed model of DFIG based RAPS system

20

4.3 A COORDINATED CONTROL APPROACH FOR HYBRID

ENERGY STORAGE.

The decision – making process associated with the control coordination

algorithm of the wind – battery/fuel cell – supercapacitor – based RAPS system is

shown in Fig.4.3. During over generation condition where the power output from the

wind turbine generator Pw is greater then the load demand PL, the hybrid energy

storage Pb (i.e., battery/fuel cell storage and super capacitor) absorbs the excess power

(PW – PL ) and it is shared between the battery/fuel cell storage system and super

capacitor according to the power management algorithm.

If the capacity of the hybrid energy storage system reaches the maximum limit

or (Pb)max, the dump load needs to absorb the excess power. However, if the dump

load power Pd reaches its maximum limit rating (Pd) max, the pitch angle control has to

be activated in order to reduce the power output of the wind turbine generator.

During under generation situations where the power output of the wind

turbine generator is less than the load demand, i.e., (PW – PL ) < 0, it is assumed that

the hybrid energy storage Pb is able to supply the required power deficit (PL – PW).

During emergency situations such as no power output from wind turbine

generator due to wind speed being below cut – in level or above cut – out level, a load

shedding scheme can be implemented. Moreover, the proposed control coordination

concept has been realized by developing the control strategies for each component of

the RAPS system.

21

Figure 4.3: A Coordinated control approach for hybrid energy storage based

RAPS system

Power management algorithm

Wind Power

Pw

Vcut-in<V<Vcut-out

Pw-PL>0

Pw=0

Hybrid energy

storage system-

discharging

Pw+Pb+Psc

-PL>0

Load

shedding

Hybrid energy storage

system-battery/fuel cell

charging

Battery/Fuel cell

– low frequency

component

Super capacitor

–high frequency component

Pb<(Pb)max Dump

Load

“ON”

Pd <(Pd)max Pitch

Regulation

Frequency

control

NO

NO

NO

NO

NO

Battery/Fuel cell discharging

Battery/Fuel cell

charging

Yes

Yes

Yes

Yes

Yes

22

4.4 THE POWER MANAGEMENT ALGORITHM.

Depending on the objectives to be achieved i.e., minimization of the demand –

generation mismatch and ensuring safe operation of the energy storage systems, a

power management algorithm is designed and implemented for the hybrid energy

storage system. The proposed power management algorithm is designed in such a way

that the supercapacitor should be able to absorb the ripple or high – frequency power

component of demand – generation mismatch leaving the steady component for the

battery/fuel cell storage system. The power management algorithm is implemented

encompassing the battery/fuel cell storage and super capacitor storage with a view to

achieve the following objectives:

To help maintain the power balance of the RAPS system.

To maintain voltage and frequecy at the PCC.

To improve the performance of the fuel cell/battery storage system by

reducing ripple current and high rate of DOD of battery.

The first objective is achieved by generating the input signal for the controllers

of the hybrid energy storage system using the demand – generation mismatch (Pw−PL)

of the RAPS system. To realize the second objective, a controlling scheme associated

with RSC and LSC are developed.

Under heavy DOD levels, the battery storage attains quick charge regulation.

Therefore, the third objective is related to managing the DOD levels of the battery

storage system, which is achieved by separating the demand – generation mismatch

into two frequency components through a high – pass filter, as shown in Fig.4.4.

Figure 4.4: Estimation of reference power for battery/fuel cell and super

capacitor

23

Figure 4.5: Operating frequency ranges for storage system

The demand – generation mismatch is explained by two frequency regions,

which can be given by Eq.(4.1). The high – frequency power component of the

demand – generation mismatch Phf is used to estimate the reference current of the

supercapacitor (ic)ref. Contrarily, the low – frequency power component of the demand

– generation mismatch Plf is used to generate the reference current of the battery/fuel

cell storage (ib)ref. The operating frequency range of each type of energy storage

systems is diagrammatically shown in Fig.4.5.

ΔPwL = Phf + Plf (4.1)

where Phf is the high – frequency component of the demand – generation mismatch,

and Plf is the low – frequency component of the demand – generation mismatch. In

real – life applications, the operation of a supercapacitor needs to satisfy the

conditions given in Eq.(4.2)–(4.4). The first condition given by Eq.(4.2) emphasizes

the safe operating voltage of a supercapacitor, which is usually indicated by the

manufacturer in data sheet. The second condition given by Eq.(4.3) indicates the

maximum possible peak current of a supercapacitor. The third condition presented in

Eq.(4.4) defines the maximum allowable power from the supercapacitor during its

operation.

(Vsc )min < Vsc < (Vsc )max (4.2)

(Ic)pk =(0.5 Csup Vsc )

Csup ES Rdc +1 (4.3)

(Psc )max = ±Csup Vsc dVsc

dt max (4.4)

where Csup is the capacitance value of the supercapacitor; (vsc)max, (vsc)min are

maximum and minimum operating voltages of supercapacitor, respectively; ESRdc is

the equivalent series resistor of the supercapacitor, (Psc)max is the maximum power

24

rating of the capacitor, and dVsc

dt max is the maximum rate of change of voltage

across the supercapacitor.

Figure 4.6: Types of super capacitor

The size estimation of the battery/fuel cell energy storage and supercapacitor

is extremely design specific for a given site or an application. However, in the present

case, the value of the capacitance of the supercapacitor is estimated considering the

worst case scenario where it is able to supply energy subjected to the wind energy

inverter constraints over a certain time period t, as given by Eq.(4.5) and Eq.(4.6).

Esc = (Smax (PDFIG )rated )t (4.5)

( Csup ) =2Esc

((Vsc )max )2−((Vsc )min )2

(4.6)

4.5 BATTERY/FUEL CELL STORAGE FUNCTION.

The battery/fuel cell storage is used to meet the steady component of the

demand – generation mismatch, thus avoiding higher depths of discharging. The

controlling of battery/fuel cell is designed according to Eq.4.7.

Storage system status =

PDFIG > PL ; charging mode PDFIG < PL; charging mode

PDFIG = PL ; idling mode

(4.7)

During over – generation, power output of the wind turbine generator PDF IG

is greater than the load demand PL and hence the battery/fuel cell acts as a load

while operating on charging mode .Contrarily, during under – generation conditions

the battery/fuel cell storage operates on discharging mode. Under balanced

operating conditions where the wind power output matches with the load demand, the

battery/fuel cell storage system stays at the idling mode.

(a) (b)

25

As shown in Fig.4.1 and Fig.4.2, an inverter is used to interface the

battery/fuel cell storage system with the RAPS system. The inverter control associated

with the storage system is developed by following the power management algorithm

and depicted in Fig.4.7. The reference current of the (ib)ref is generated considering

the low – frequency component of the demand – generation mismatch Plf, as given in

Eq.(4.8). The inverter is operated at unity power factor by setting (iqs)ref equal to zero.

(Ib)ref = (Plf + Pb)(kp +ki

s) (4.8)

where Pb is the actual power, and kp and ki are the proportional and integral

gains of the PI controller, respectively.

4.5.1 ESTIMATION OF BATTERY

The capacity estimation of the battery storage system depends on many factors

such as wind profile and load demand. The size of the battrey system is estimated

using Eq.(4.9)

μ × irated × t

60 = (Ah rating) × k′ (4.9)

where, μ is fraction of the rated current of the load demand, irated is the rated curent

corresponding to load demand, t is the time duration over which the battery provides

power to the system, k′ is the average discharge/charge current of the battery storage

in pu.

4.5.2 ESTIMATION OF FUEL CELL

The estimation of the size of a fuel cell system is extremely application

specific and depends on many factors such as wind profile and wind generator

capacity. In this thesis, the fuel cell system is sized to provide 25% of the rated load

demand which also satisfies the constrains associated with the rating of inverter.

26

Figure 4.7: Inverter control

4.6 SUPER CAPACITOR AND DUMP LOAD.

The low – frequency model of a supercapacitor consisting of a capacitor,

which can be used under power system operating frequency range, is employed in the

project. The super capacitor system is connected to the DC bus using a bi –

directional buck – boost converter as shown in Fig.4.8.

Figure 4.8: Buck – Boost converter

27

Super capacitor status =

PDFIG > PL ; charging mode (buck operation) PDFIG < PL ; charging mode (boost operation)PDFIG = PL ; idling mode

(4.10)

The controller for the super capacitor storage system is developed with a

view to achieve two objectives. Firstly, it should be able to minimise the demand

– generation mismatch. Secondly, the controller helps in extracting the maximum

amount of power from wind allowing the wind turbine generator to operate in its

optimum mode. The demand – generation mismatch of the RAPS system can be

estimated based on Eq. (4.10) and is used to obtain the reference super capacitor

current, (isc)ref . To achieve the second objective, optimum wind power from the

DFIG is considered as one of the inputs to estimate the reference super capacitor

current as given in Eq. (4.11).

(isc )ref = (PDFIG )opt − PL

Vsc (4.11)

where, PL is load demand, vsc is super capacitor voltage and (PDF IG)opt is

optimum power from DFIG.

For grid connected DFIG applications, the q – axis component of rotor

current iqr is used to extract the maximum power from wind using RSC converter

control. Contrarily, in standalone mode of operation, the current iqr, is utilised to

operate the RSC in SFO mode as given by Eq (4.12).

iqr = (−Ls

Lm)iqs (4.12)

Therefore, iqr cannot be directly used to extract the maximum power from

wind during standalone operation of the wind turbine generator. Instead, the

condition given by E q . (4.13) can be regarded as an indirect technique in

harvesting the maximum power from wind compared to grid – connected operation.

The key idea behind the proposed indirect maximum power extraction strategy is to

regulate the power flow of the super capacitor storage in a manner that helps in

extracting maximum power from wind by imposing an appropriate toque as in

Eq.(4.14). When the DFIG operates at the maximum power extraction mode, the

torque generated by the DFIG given in Eq.(4.14) should be equal to the optimum

torque as in Eq.(4.13).

28

As evident from Eq.(4.15), the maximum power extraction from DFIG can

be realised by varying iqs, the q – axis component of the stator current. Therefore,

by allowing the super capacitor current as given in Eq.(4.16), it is possible to vary iqs

resulting DFIG to operate on maximum power extraction mode.

(Te)opt = Kopt (ωr)2 (4.13)

Te =Lm

Ls +Lm

Vs

ωr iqr (4.14)

ωr = (Lm Vs

(Ls +Lm )Kopt) iqs (4.15)

where, Te is electromagnetic torque of the DFIG, iqr, iqs are rotor and stator

q-axis currents respectively, Ls, Lm are stator inductance and magnetising

inductance respectively.

(isc )ref =Phf

Vsc (4.16)

Therefore the high – frequency component of the demand – generation

mismatch Phf is met by the supercapacitor where the corresponding reference current

(isc)ref is estimated using Eq. (4.16). The adopted control strategy for the

supercapacitor is illustrated in Fig.4.9.

Figure 4.9: Super capacitor controlling strategy.

4.6.1 ESTIMATION OF SUPERCAPACITOR

The supercapacitor is used to supply smax times the rated capacity of the DFIG

power, i.e., PDFIG. The safe operating voltage limits associated with the supercapacitor

are selected to be as follows:

250 V < vsc < 500 V (4.17)

29

Assuming that, in the worst case, the supercapacitor is able to provide the

maximum slip power of DFIG smax PDFIG for time t = 10s, the capacitance value of the

supercapacitor can be calculated as follows:

C=(Smax (PDFIG )rated )t

((Vsc )max )2−((Vsc )min )2 (4.18)

C=(3×750×1000×10×2)

(5002−2002)≈ 20F (4.19)

4.6.2 DUMP LOAD CONTROLLER

Due to the limited power capacity associated with the back – to – back

converter system, the DC bus of the back – to – back converter is not identified as the

best location to connect the dump load. Noting this issue, a dump load can be suitably

located in AC side of the system where the capacity of the dump load is not restricted

by any inverter. The operation of dump load is enabled when the battery/fuel cell

storage reaches its maximum capacity. Therefore, the condition under which the

dump load operation is enabled is given by Eq.(4.20).

Figure 4.10: Dump load control strategy.

It is to be noted that the contribution of the supercapacitor power is not

considered in the process of estimating the dump load power considering its

performance in a short – term window and a high – frequency domain. The simplified

schematic of the dump load controller is shown in Fig.4.10.

Pd = Pd, (Pw) + (Pb)max − PL > 0

0, otherwise (4.20)

where Pw is the power output of the DFIG, and (Pb)max is the maximum

capacity of the battery/fuel cell storage system.

30

4.7 CHAPTER SUMMARY

This chapter addresses the modelling of DFIG based RAPS system and

benefits of integrating a super capacitor and a battery/fuel cell storage system. In this

regard, an energy management algorithm (EMA) has been established and in addition

a control coordinated strategy is implemented to coordinate the power flow between

the system components.

31

CHAPTER 5

SIMULATION MODEL AND RESULTS

This chapter presents the relevant study of two simulation models of hybrid

energy storage DFIG based wind dominated RAPS system. Section 5.1 describes

about simulation model with battery and super capacitor as hybrid energy storage

system. In section 5.2, simulation model with fuel cell and super capacitor as hybrid

storage system is studied. Section 5.3 presents results obtained for both the simulation

models under various wind speed and variable load. Finally section 5.4 gives a

comparative study of battery and fuel cell storage system.

5.1 SIMULATION MODEL WITH BATTERY AND SUPER

CAPACITOR AS HYBRID STORAGE SYSTEM

The proposed model is designed in simulink tool of MATLAB 2009b as in

Fig.5.1. The simulation model started with the designing of DFIG. As it is known that

DFIG is asynchronous generator feeding power from both stator and rotor, and can

operate for variation in wind of ±30%. So Asynchronous machine with pu units

measurements is used. The ratings are assigned according to the values mentioned in

appendix. The stator side is connected to the Line Side Converter and the rotor

windings are connected to the Rotor Side Converter. The mechanical input torque

which is used to run the machine is generated through wind turbine block.

Using the wind turbine block the wind speed at which the generator should

operates, the pitch angle and generator speed are specified. Its known that wind speed

is never constant and varies with time to time, so using a timer block a variable wind

is generated which initially makes the generator to run at 12 m/s and then at 3 second

it drops to 9 m/s and again at 5 seconds it raised to 11 m/s. Using the bus selector the

stator current, rotor currents and rotor speed of DFIG are measured which further used

in controlling schemes of converters.

32

Figure 5.1: Simulation circuit with battery and super capacitor

33

5.1.1 RSC AND LSC DESIGN.

The line side converter and rotor side converter are IGBT universal bridge,

which acts as converter performing inverter and rectifier operation depending on the

operation required. The input pulses for both the converter are generated as per the

individual controlling technique designed for RSC and LSC. The complete operation

of LSC and RSC is explained in chapter 3 section 3.2 and 3.3.

Figure 5.2: RSC controlling circuit

The Rotor side converter controlling as shown Fig.5.2 is designed according to

the description mentioned in section 3.2 of chapter 3. The discrete 3 – phase PLL used

is used to track the frequency and phase of a sinusoidal 3 – phase signal by using an

internal frequency oscillator. The control system adjusts the internal oscillator

frequency to keep the phase difference zero. Therefore it concludes that PLL is mainly

used to synchronize grid with the wind.

The proportional and integral controller is used to increase the speed of the

response and also to eliminate the steady state error. The dqo_to_abc transformation

block also called as parks transformation is used to convert dqo to abc and this is

34

given as an input to discrete PWM generator. Pulses given to gate signal of RSC are

generated by using this block. The output of PWM acts as input to unit delay which is

used to hold and delay the input by the sample time specified.

Figure 5.3: LSC controlling circuit

The Line Side Converter as in Fig.5.3 is designed according to section 3.3 in

chapter 3. The outer loop is used to maintain the DC link voltage. The desired DC

voltage that is to be maintained (750 V) is compared with Vdc which is the output

from capacitor. The difference is passed through PI controller and the stabilized

output is then compared with Iqs and the difference is passed through PI controller.

The stabilized output is then compared with Vds and Iqs as explained in chapter 3. The

second loop is used to maintain reactive power zero. Finally dqo are converted to abc

by using parks transformation block and then this is given as input to PWM and pulses

are generated and delayed by a sample time and given to the gate of LSC.

35

5.1.2 BATTERY/FUEL CELL, SUPERCAPACITOR AND DUMP LOAD

CONTOL

The battery/fuel cell controlling is designed according to the section 4.5 of

chapter 4. The Super capacitor controlling is designed according to section 4.6 of

chapter 4 where the outer loop measures the DC link voltage VDC, which is compared

with the reference DC link voltage (Vdc)ref, and the error is compensated through a PI

controller to generate the reference current (Isc)ref. This current is then compared with

the actual super capacitor current isc, and the corresponding error is compensated

through second PI controller to generate the switching signal for DC – DC converter.

The main objective behind this control is to regulate the generator current which is

directly proportional to the load toque of the generator.

The Dump load is controller in designed in such a way that it operates when

the battery power, wind power and super capacitor power exceeds. This excess power

is absorbed by the dump load.

5.2 SIMULATION MODEL WITH FUEL CELL AND SUPER

CAPACITOR AS HYBRID ENERGY STORAGE

The simulation model with fuel cell and super capacitor is designed same as

that of simulation model 1. Since fuel cell are more efficient and has life cycle more

than batteries, so batteries are replaced by fuel cell. The function of fuel cell is same

as that of battery, so controlling is designed same as battery controlling. The

simulation model is shown in Fig.5.4.

36

r

Figure 5.4: Simulation model with fuel cell and super capacitor

37

5.3 PERFORMANCE OF THE HYBRID ENERGY STORAGE

SYSTEM BASED DFIG SYSTEM.

The torque and speed characteristics of DFIG are shown in Fig.5.5. The

negative torque represents the generating mode.

Figure 5.5: Torque and Speed of DFIG

5.3.1 BATTERY AND SUPER CAPACITOR RESULTS

The system response of the DFIG based RAPS system with battery and super

capacitor as hybrid storage system is shown in Fig.5.6 – Fig.5.9 whereas Fig.5.10 –

Fig.5.13 illustrates the power sharing between different system components.

The wind condition under which the system has been simulated is shown in

Fig.5.6. It can be seen that the wind velocity is set initially at 12 m/s. At t = 3 s, the

wind velocity drops to 9 m/s, and it increases to 11 m/s at t = 7 s.

ωr

Te

Tsec

38

Figure 5.6: Wind speed (Battery)

The voltage on load side is shown in Fig.5.7 which is seen not to be affected

by the wind speed or load changes. This proves that the DFIG controllers are able to

maintain voltage constant. The load voltage of the system stays 1 pu ( ±2% of its

rated value) throughout the operation.

Figure 5.7: Voltage on load side (Battery)

The operating frequency of the RAPS system is shown in Fig.5.8. The

operating frequency is closely regulated at its rated value of 50 Htz i.e., 1 pu and is

seen not to be influenced by the wind speed or load step changes. Furthermore, it can

W s

Vload

(pu)

Tsec

Tsec

39

be seen that the frequency of the system is maintained within 0.2% of its rated

value.

Figure 5.8: Frequency on load side (Battery)

It can be noted that, the super capacitor quickly changes its direction of

power flow as evident from Fig.5.12 which causes the fluctuations in the DC link

voltage. However, as seen from Fig. 5.9 even during such transient conditions, the

DC link voltage variation is limited to within ±5% of its rated value.

Figure 5.9: DC link Voltage (Battery)

Tsec

Vdc

(pu)

Tsec

f(pu)

40

Figure 5.10: Load Demand (Battery)

The DFIG power output is shown in Fig.5.11. As seen in Fig.5.10, initial

load demand is set at 0.425 pu and then it is increased to a value of 0.7 pu at t=4s

and the added additional load (i.e. 0.275 pu) is disconnected from the system at

t= 6 s.

As shown in Fig.5.11, the power output of the DFIG is seen to rise to a value

of 0.6 pu at t = 2 s and the corresponding load demand is at 0.425 pu. This leads to

an over – generation condition where the excess power is shared between the

battery storage system and super capacitor as evident from Fig.5.12.

Figure 5.11: Wind Power (Battery) Tsec

Pwind

(pu)

Tsec

Pload

(pu)

41

It can be seen that the super capacitor responds to the fast varying power

variations while the battery absorbs the slow varying power variations of the

demand – generation mismatch. Also, the super capacitor responds quickly to load

step changes which occur at t = 4 s and t = 6 s avoiding high rates of DOD of the

battery storage system

Figure 5.12: Hybrid energy storage power

The battery storage system reaches its full capacity of 0.175 pu at t=2 s

leading to the operation of dump load which absorbs the additional power of 0.02

pu as evident from Fig.5.13.

Figure 5.13: Dump Load Power (Battery)

Tsec

Pd

(pu)

Tsec

Pb

(pu)

Pscp

(pu)

42

The battery storage system operates in its charging mode until load step

addition which occurs at t = 4 s leading to a change of its mode of operation

from charging to discharging. However, the rate of discharge is reduced after the

load step reduction that occurs at t = 6 s. The battery current for the case with no

super capacitor is shown in Fig.5.14.

Figure 5.14: Battery current

Figure 5.15: Hybrid Energy storage current

The battery current consists of high frequency fluctuating component and

exhibits steep DOD during load step changes. The current level of the hybrid energy

storage with the super capacitor is shown in Fig.5.15. It can be seen that the battery

Tsec

Ib

Is

Tsec

Ib

43

storage system has near ripple free current with low value of DOD rate at the time

of load step changes.

The FFT analysis of the battery current and the super capacitor current are

given in Fig.5.16 and Fig.5.17, respectively. The battery current is shown to be free

from ripples or high – frequency component, whereas the super capacitor current

consists of considerable amount of high frequencies, which ensures the safe operation

of the battery storage.

Figure 5.16: FFT analysis of the battery system

Figure 5.17: FFT analysis of the Super capacitor

5.3.2 FUEL CELL AND SUPER CAPACITOR RESULTS

5.3.2.1 Results with Constant Load

The system response of the DFIG based RAPS system for constant load with

Fuel cell and super capacitor as hybrid storage system is shown in Fig.5.18 –

Fig.5.21. whereas Fig.5.22 – Fig.5.25 illustrates the power sharing between different

system components.

44


Fig.5 . 1 8 . It can be seen that the wind velocity is set initially at 12 m/s. At t = 3 s,

the wind velocity drops to 9 m/s, and it increases to 11 m/s at t = 7 s.

Figure 5.18: Wind Speed ( Fuel cell)

The voltage on load side is shown in Fig.5.19 which is seen not to be

affected by the wind speed changes. This proves that the DFIG controllers are able to

maintain voltage constant. The load voltage of the system stays 1 pu ( ±2% of its

rated value) throughout the operation.

Figure 5.19: Voltage on load side (Fuel cell)

W s

Tsec

Vload

(pu)

Tsec

45



seen not to be influenced by the wind speed changes. Furthermore, it can be seen that

the frequency of the system is maintained within 0.2% of its rated value.

Figure 5.20: Frequency on load (Fuel cell)

Figure 5.21: DC link Voltage (Fuel cell)

The DC link voltage of the DFIG is depicted in Fig.5 .21 which is well

regulated rated value throughout the operation.

Tsec

Vdc

(pu)

Tsec

f (pu)

46

Figure 5.22: Load Demand (Fuel cell)

The DFIG power output is shown in Fig.5.23,.As seen in Fig.5.22, load

demand is set at 0.425 pu throughout the operation.

Figure 5.23: Wind Power (Fuel cell)



an over – generation condition where the excess power is shared between the fuel

cell storage system and super capacitor as evident from Fig.5.24.

Tsec

Pwind

(pu)

Tsec

Pload

(pu)

47

Figure 5.24: Hybrid energy storage power

The fuel cell storage system reaches its full capacity of 0.175 pu at t=2 s



Figure 5.25: Dump Load Power (Fuel cell)

The fuel cell storage system operates in its charging mode. The battery

current and super capacitor current is shown in Fig.5.26.

Tsec

Pd

(pu)

Tsec

Pfc

(pu)

Pscp

(pu)

48

Figure 5.26: Hybrid Energy storage current

5.3.2.2 Results with Variable Load

The system response of the DFIG based RAPS system with fuel cell and

super capacitor as hybrid storage system is shown in Fig.5.27 – Fig.5.30, whereas

Fig.5.31 – Fig.5.34 illustrates the power sharing between different system

components.


Fig.5 . 2 7 . It can be seen that the wind velocity is set initially at 12 m/s. At t = 3 s,

the wind velocity drops to 9 m/s, and it increases to 11 m/s at t = 7 s.

Figure 5.27: Wind Speed (Fuel cell)

Ifc

Is

W s

Tsec

Tsec

49

The voltage on load side is shown in Fig.5.28 which is seen not to be

affected by the wind speed or load changes. This proves that the DFIG controllers are

able to maintain voltage constant. The load voltage of the system stays 1 pu ( ±2%

of its rated value) throughout the operation.

Figure 5.28: Voltage on Load Side (Fuel cell)



seen not to be influenced by the wind speed or load step changes. Furthermore, it can

be seen that the frequency of the system is maintained within 0.2% of its rated

value.

Figure 5.29: Frequency on Load Side (Fuel cell)

Tsec

Tsec

f (pu)

Vload

(pu)

50

Figure 5.30: DC Link Voltage (Fuel cell)

The DC link voltage of the DFIG is depicted in Fig.5.30 which is well

regulated rated value throughout the operation except during load changes at 4 s and

6 s. However, the highest DC link voltage variations are seen to occur at t= 4 s and

t= 6 s which correspond to the load step changes as evident from Fig.5.31.

It can be noted that, the super capacitor quickly changes its direction of

power flow as evident from Fig.5.33 which causes the fluctuations in the DC link

voltage. However, even during such transient conditions, the DC link voltage

variation is limited to within ±5% of its rated value.

Tsec

Vdc

(pu)

51

Figure 5.31: Load Demand (Fuel cell)

The DFIG power output is shown in Fig.5.32. As seen in Fig.5.31, initial

load demand is set at 0.425 pu and then it is increased to a value of 0.7 pu at t =

4 s and the added additional load (i.e. 0.275 pu) is disconnected from the system

at t= 6 s.

Figure 5.32: Wind Power (Fuel cell)



an over – generation condition where the excess power is shared between the fuel

cell storage system and super capacitor as evident from Fig.5.33.

Tsec

Pwind

(pu)

Tsec

Pload

(pu)

52

It can be seen that the super capacitor responds to the fast varying power

variations while the fuel cell absorbs the slow varying power variations of the

demand – generation mismatch. Also, the super capacitor responds quickly to load

step changes which occur at t = 4 s and t = 6 s avoiding high rates of DOD of the fuel

cell storage system.

Figure 5.33: Hybrid Energy Storage Power

The fuel cell storage system reaches its full capacity of 0.175 pu at t=2 s



Figure 5.34: Dump Load Power ( Fuel cell) Tsec

Pd

(pu)

Tsec

Pfc

(pu)

Pscp

(pu)

53

The fuel cell storage system operates in its charging mode until load step

addition which occurs at t = 4 s leading to a change of its mode of operation

from charging to discharging. However, the rate of discharge is reduced after the

load step reduction that occurs at t = 6 s. The battery current for the case with no

super capacitor is shown in Fig.5.35.

Figure 5.35: Fuel Cell Current

Figure 5.36: Hybrid Energy Storage Current

The Fuel cell current consists of high frequency fluctuating component and

exhibits steep DOD during load step changes. The current level of the hybrid energy

storage with the super capacitor is shown in Fig.5.36.

Tsec

Ifc

Is

Tsec

Ifc

54

5.4 COMPARISON OF BATTERY AND FUEL CELL AS

STORAGE SYSTEMS.

Analysing the results of battery and fuel cell integrated with super capacitor it

is seen that both function equally to variations in wind speed and load, thus providing

same storage function.

As theoretically seen from [15], [16], [17] basic fuel cells run on pure

hydrogen so they are pollution free, giving off only electricity, water, and heat. The

potential for fuel cells to provide zero or near – zero emissions has forced to develop

this technology over the past 30 years, and is drawing increasing attention to the

technology today. The advantages of fuel cell over battery are:

There is no combustion in a fuel cell, so fuel is converted to electricity more

efficiently than any other electrical generating technology available today.

Unlike batteries that must be disposed of once their chemicals are used up,

fuel cell reactions do not degrade over time and can provide continuous

electricity.

Traditional power plants must be large in order to gain efficiency, but fuel

cells can achieve higher efficiencies at any scale, making them perfect for

small portable, residential, and transportation uses.

Because fuel cells are clean and efficient at any size, they can be located

almost anywhere, including dense urban areas where both air quality and

transmission congestion may be of concern. Fuel cells can offer an alternative

to building new power lines. Fuel cells can provide more reliable power

wherever electricity is needed, making the whole electric power grid more

robust and reliable.

Economically, fuel cells represent a prudent path to provide the country's

electric power because they can be installed quickly, are fuel flexible, and can

be put in place incrementally, mitigating the need for more costly and

sweeping changes.

5.5 CHAPTER SUMMARY

In this chapter simulation studies have been conducted of the proposed system.

Based on simulation results, following conclusion was drawn:

DFIG based RAPS system with hybrid energy storage system are able to

55

regulate the voltage and frequency at PCC within limits.

DC link voltage was maintained at 750 V.

Battery and super capacitor responded efficiently depending on increase in

demand as observed form section 5.3.1.

Fuel cell and super capacitor responded efficiently depending on increase in

demand as observed form section 5.3.2.

At last, comparison of battery and fuel cell is done.

56

CHAPTER 6

CONCLUSION AND FUTURE SCOPE

6.1 CONCLUSION

In this thesis, through simulation studies it can be concluded that hybrid

storage systems is capable in maintaining the voltage and frequency at the load end.

Also, it has been noted that the power sharing between the systems components was in

accordance with the proposed coordinated control methodology. The thesis has also

addressed the benefits of integrating a super capacitor to a battery / fuel cell storage

system and also explains the benefits of fuel cell when compared to battery in a wind

– based hybrid RAPS system.

When considering the operation of battery / fuel cell storage systems,

avoidance of heavy DOD rates and reduced ripple content in the battery / fuel cell

current is given importance. To solve above problem, a super capacitor was integrated

with the battery storage system to form the hybrid energy storage (i.e. battery / fuel

cell and super capacitor) and improving battery’s / fuel cell’s performance. It has also

been noted that the super capacitors integrated to the DFIG was able to handle the

transients caused by wind speed and load changes effectively. Charging and

discharging of battery makes it to run for only for few years and thus requires heavy

maintenance. To avoid this problem, batteries are replaced with fuel cells that can

provide continuous electricity for several years [18].

Thus concluding by stating that application of hybrid storage system to DFIG

based wind dominated RAPS systems is capable in maintaining the voltage and

frequency at the load end with proper power sharing between the devices.

6.2 FUTURE SCOPE

As extensions to the work presented in this thesis, following is a description of further

activities that can be undertaken in relation to standalone RAPS system:

Development of the control strategies for each component of RAPS systems

with a view to operate them under unbalanced load conditions.

Integration of other types of renewable energy systems (e.g. solar

photovoltaic) to wind based RAPS systems.

57

Further development of the existing control strategies of the RAPS systems to

operate as a grid interactive micro – grid.

58

REFERENCES

[1] http://www.mnre.gov.in.

[2] S. Bhattacharyya (ed.), Rural Electrification Through Decentralised Off-grid

Systems in Developing Countries, Green Energy and Technology, DOI:

10.1007/978-1-4471-4673-5_2, Springer-Verlag London 2013.

[3] Doubly fed induction generator system for wind turbine by BY S.

MÜLLER,M. DEICKE, & RIK W. DE DONCKER May/June 2011.

[4] N. Mendis, K. M. Muttaqi “Management of Low- and High-Frequency Power

Components in Demand-Generation Fluctuations of a DFIG-Based Wind-

Dominated RAPS System Using Hybrid Energy Storage,” IEEE Transactions

on Industry Applications, Vol. 50, No. 3, May/June 2014.

[5] John Fletcher and Jin Yang (2010). Introduction to the Doubly-Fed Induction

Generator for Wind Power Applications, Paths to Sustainable Energy, Dr Artie

Ng (Ed.), ISBN:978-953-307-401-6.

[6] Literature review paper on doubly fed induction generator wind turbine

technology Ajay Kushwaha1, Inderpreet Singh2 1,2EIED, Thapar University,

Patiala, Punjab, IndiaISSN: 2319-7463 Vol. 2 Issue 9, September-2013.

[7] Krisztina Leban. Doubly Fed Induction Generator Fault Simulations. PhD

thesis, Institute of Energy Technology, Aalborg University, Alborg, Denmark,

2009.

[8] R. Pena, J. C. Clare, and G. M. Asher. Doubly fed induction generator using

back – to – back pwm converters and its application to variable – speed wind –

energy generation. IEE Proceedings - Electric Power Applications, 143(3):231

– 241,May 1996.

[9] D. Santos-Martin, S. Arnaltes, and J. L. R. Amenedo. Reactive power

capability of doubly fed asynchronous generators. Journal of Electric Power

Systems Research, 78(11):1837 – 1840, Nov. 2008.

[10] P. F. Ribeiro, B. K. Johnson, M. L. Crow, A. Arsoy, and Y. Liu, “Energy

storage systems for advanced power applications,” Proc. IEEE, vol. 89, no. 12,

pp. 1744–1756, Dec. 2001.

[11] M.Beaudin,H.Zareipour,A.Schellenberglabe,andW.Rosehart,“Energy storage

for mitigating the variability of renewable electricity sources: An updated

review,” Energy Sustainable Develop., vol. 14, no. 4, pp. 302– 314, Dec.

2010.

59

[12] Kuldeep Sahay; Bharti Dwivedi; “Design and Analysis of Supercapacitors

Energy Storage System for Energy Stabilization of Distribution Network” in

Electrical Power Quality and Utilisation Journal Vol.XV, No.1, 2009.

[13] T. Patrick and Moseley, “Energy storage in remote area power supply

(RAPS)systems,”J.PowerSources,vol.155,no.1,pp.83–87,Apr.2006.

[14] W. Li, G. Joos, and J. Belanger, “Real-time simulation of a wind turbine

generator coupled with a battery supercapacitor energy storage system,” IEEE

Trans. Ind. Electron., vol. 57, no. 4, pp. 1137–1145, Apr. 2010.

[15] P. Thounthong, S. Rael, and B. Davat, “Control strategy of fuel cell and

supercapacitors association for a distributed generation system,” IEEE Trans.

Ind. Electron., vol. 54, no. 6, pp. 3225–3233, Dec. 2007.

[16] R. K. Shah “Introduction to fuel cells”

[17] Paul Kaeser, Kantonsschule Baden “Batteries” May 2010

[18] http://www.altenergy.org/renewables/fuel_cells.

60

APPENDIX

A.1 PARAMETERS ASSOCIATED WITH DFIG BASED RAPS

SYSTEM.

Table A.1: Parameters

S.No. PARAMETERS RATINGS

1. Rated power output (PDFIG) 750 kW

2. Stator resistence (Rs) 0.00706 pu

3. Stator leakage inductance (Lls) 0.171 pu

4. Rotor resistance (Rr) 0.005 pu

5. Rotor leakage inductance (Llr) 0.156 pu

6. Magnetising inductance (Lm) 2.2 pu

7. Inertia constant (H) 2.04 S

8. Number of pole pairs (P) 3

9. Filter inductance at LSC (Lf) 0.3 pu

10. Filter resistance at LSC (Rf) 0.003 pu

11. DC capacitance 5000e-6

12. DC bus voltage (Vdc) 750 V

13. Stator voltage ( Vs) 400 V

14. Operating frequency (fs) 50 Hz

15. Rating of battery storage system (Pb) 420 kWh

16. Capacitance of Super capacitor (C) 20 F

17. Rating of Fuel cell 50kW

18. Allowable SOC of the battery system (SOC) 40 % - 80 %

19. Rated dump load power ((Pd)max) 20 kW

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