COMPOSITE FES AND CAES FOR REGULATION OF GRID

PARAMETERS

SEMINAR REPORT

submitted by

VISHNU N NAMBOOTHIRI
(CHN17EE091)

to
the APJ Abdul Kalam Technological University
in partial fulfillment of the requirements for the award of the Degree of
Bachelor of Technology
in
Electrical and Electronics Engineering

Department of Electrical and Electronics Engineering

College of Engineering, Chengannur-689121

JANUARY, 2021
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
COLLEGE OF ENGINEERING, CHENGANNUR

Certificate

Certified that this is a bonafide record of the seminar report entitled

“COMPOSITE FES AND CAES FOR REGULATION OF GRID
PARAMETERS” done by VISHNU N. NAMBOOTHIRI (CHN17EE091)
during the year 2020 in partial fulfillment of the requirements for the award of
the Degree of Bachelor of Technology in Electrical and Electronics Engineering
of APJ Abdul Kalam Technological university Kerala

Dr. Rajeevan A.K Dr. Bindu C.J.

Assistant Professor Head of Department
Seminar Coordinator Electrical & Electronics

Chengannur
Date : 14/01/2021
 ACKNOWLEDGMENT

The success and final outcome requires a lot of guidance and assistance from many
people and I am extremely fortunate to have all these along the completion of this
seminar work. I would like to extend my sincere and heartfelt obligation to
management, College of Engineering, Chengannur for their support and for
providing necessary infrastructure. I would like to extend my sincere thanks to Dr.
Jacob Thomas V. , Principal of our college for his kindest support. I am greatly
obliged to Dr. Bindu C.J. , Head of Department of Electrical And Electronics, for
the encouragement and support she has provided. I am immensely indebted to our
seminar coordinator, Dr. Rajeevan A.K, Asst. Professor in Electrical Department,
for the guidance, advice to accomplish the seminar. On this occasion, I also
remember the valuable suggestions offered by my family members, classmates and
friends which are inevitable for the successful completion of my seminar.

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 ABSTRACT

The seminar discusses a system proposing Composite Flywheel Energy Storage(FES) and
Compressed Air Energy Storage(CAES) system for the regulation of grid parameters. The system
consists of a flywheel energy storage which can charge and discharge power with variation in
frequency, thereby keeping a desired frequency in power grid and a compressed air energy
storage which charge and discharge energy for peak regulation, phase modulation and for
blackstart. The FES stores energy as rotational kinetic energy which is suitable for short and
sudden grid disturbances. The CAES stores energy in the form of compressed air and expander
delivers it back to grid when required.

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 TABLE OF CONTENTS

CONTENTS Page No.

ACKNOWLEDGEMENT i
ABSTRACT ii
LIST OF FIGURES iv
ABBREVIATIONS v
NOTATION v
Chapter 1. OBJECTIVE 1
Chapter 2. INTRODUCTION 2
Chapter 3. LITERATURE SURVEY 3
Chapter 4. METHODOLOGY 4
4.1 Storage Systems 4
4.1.1 Flywheel Energy Storage(FES) 4
4.1.2 Compressed Air Energy Storage(CAES) 6
4.2 Proposed System 7
Chapter 5. CHALLENGES 10
Chapter 6. CONCLUSION 12
REFERENCES 13
APPENDIX 14

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 LIST OF FIGURES

No. Title Page No.

4.1 Schematic diagram of FES 4

4.2 Back-to-Back converter 6
4.3 CAES 7
4.4 Block diagram of proposed system 7
4.5 CAES with synchronous condenser 8
4.6 CAES with blackstart 9
5.1 News on Beacon Plant explosion 10
5.2 LightSail Energy 11

iv
 ABBREVIATIONS

AC Alternating Current
CAES Compressed Air Energy Storage
DC Direct Current
FES Flywheel Energy Storage
MG Motor-Generator

NOTATION

𝑓 Frequency, Hetz
𝐼 Current, ampere
𝑚 Mass, Kilogram
𝑃 Power, watt
𝑉 Voltage, volt

Greek Symbols

𝜔 Angular Frequency, radians/second

Subscripts

𝑚𝑖𝑛 Minimum
𝑚𝑎𝑥 Maximum

v
 CHAPTER 1
OBJECTIVE

To study a paper proposing a composite storage system for power grid frequency
regulation, peak regulation, black start and phase modulation.

1
 CHAPTER 2
INTRODUCTION

In a fast progressing world, need for energy is inevitable. Electricity is the most convenient form
of energy that we can transmit from one place to another and we can use as we need. The
electricity that we use is a secondary energy source because it is produced by converting primary
sources of energy such as coal, natural gas, nuclear energy, solar energy, and wind energy, into
electrical power. Electricity is also referred to as an energy carrier, which means it can be
converted to other forms of energy such as mechanical energy or heat.
It is an amazing discovery by mankind, makes us to realize that the water in the Idukki dam can
heat the food, cool the food, run a computer, television, fan etc. It is everywhere, in our homes,
hospitals, colleges, industries. For this to happen, we need to generate, transmit and distribute the
energy. Now a days, we could identify some problems in generation side that, it is not friendly
towards the environment and makes difficult for our future human lives on earth. We generate
electricity from fossil fuels which has higher carbon emissions and affecting the quality of air.
There come renewable energy sources. We can generate electricity from wind, solar radiation etc.
But the problem is they are intermittent. But the demand of power doesn’t mind the power
generation. So there comes the concept of storing energy. We use batteries but, they have many
problems such as less life cycle, hazardous chemicals present in them. We need to look for another
methods to store the energy. One of them is Flywheel Energy Storage (FES)[2][3], converting
electricity to kinetic energy. Another way is Compressed Air Energy Storage (CAES)[4], which
stores energy by compressing the air. So the problems are, we want to get rid-off fossil fuels and
we are forced to use renewable energy sources and their penetration in grid cause problems. So
we need to solve these by implementing those storage technique. The paper[1] discuss a solution
for this problem by a composite FES and CAES for regulation of grid parameters. FES is used
for frequency regulation and CAES for peak modulation, phase modulation and black start.

2
 CHAPTER 3
LITERATURE SURVEY
The paper[1] gave an overall idea of the composite system proposed. It discussed the
characteristics of the CAES and FES systems, the functions of power grid peak frequency
modulation, black start, and phase modulation. Based on the research of the operating
characteristics of CAES, one system composited of peak-load modulation and frequency
modulation is proposed, which makes full use of the large capacity of CAES, the rapid response
of charge and discharge of the flywheel energy storage system and the significant frequency of
charge and discharge. The CAES power station has the capability of self-starting through
optimized design. After the failure of the power system, it can work as black start power supply.
After adding phase adjustment valve and pipeline, it can realize the function of phase modifier,
which has broad application and promotion space in the power grid.

The paper[2] presents a critical review of FESS in regards to its main components and
applications, an approach not captured in earlier reviews. Additionally, earlier reviews do not
include the most recent literature in this fast-moving field. A description of the flywheel structure
and its main components is provided, and different types of electric machines, power electronics
converter topologies, and bearing systems for use in flywheel storage systems are discussed. The
main applications of FESS are explained and commercially available flywheel prototypes for each
application are described.

In this paper[3], energy storage systems used in power system applications are surveyed focusing
on flywheel energy storage systems. It concluded that Flywheel Energy Storage Systems (FESS)
is of the most preferable energy storage systems to be applied in electrical power systems. FESS's
principle of operation, FESS main components (e.g. flywheel, motor/generator types, rotor
bearings, containment, power electronics, controllers), and finally FESS applications had been
also reviewed in this paper

The paper[4] presents the design scheme for multi-stage regenerative non-supplementary fired
compressed air energy storage system from the aspects of optimization design, analysis and
modeling, efficiency, as well.

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 CHAPTER 4
METHODOLOGY

4.1 STORAGE SYSTEMS

4.1.1 FLYWHEEL ENERGY STORAGE (FES)

A flywheel stores energy that is based on the rotating mass principle. It is a mechanical storage
device which emulates the storage of electrical energy by converting it to mechanical energy. The
energy in a flywheel is stored in the form of rotational kinetic energy. The input energy to the
FESS is usually drawn from an electrical source coming from the grid or any other source of
electrical energy. The flywheel speeds up as it stores energy and slows down when it is
discharging, to deliver the accumulated energy. The rotating flywheel is driven by an electrical
motor-generator (MG) performing the interchange of electrical energy to mechanical energy, and
vice versa. The flywheel and MG are coaxially connected, indicating that controlling the MG
enables control of the flywheel.

STRUCTURE AND COMPONENTS OF FES

FES system consist of a spinning rotor, MG, bearings, a power electronics interface, and
containment or housing. A typical flywheel system suitable for ground-based power is
schematically shown in figure 4.1.

Figure. 4.1 : Schematic diagram of FES

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 Flywheel Rotor

The stored energy in a flywheel is determined by the rotor shape and material. It is linearly
proportional to the moment of inertia and the square of its angular velocity, as shown in the
equation :

𝐼𝜔2
𝐸𝑛𝑒𝑟𝑔𝑦 =
2
𝑚𝑟 2 2
𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑘 𝜔
2
𝑚𝑟 2 2 2
𝑈𝑠𝑒𝑓𝑢𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑘 (𝜔𝑚𝑎𝑥 − 𝜔𝑚𝑖𝑛 )
2

𝐼 - moment of inertia
𝜔 - angular velocity
𝑘 - geometric shape factor
𝑚 - mass of rotor
𝜔𝑚𝑖𝑛 - minimum angular velocity of rotor
𝜔𝑚𝑎𝑥 - maximum angular velocity of rotor

 Motor-Generator

A machine is coupled to the flywheel to enable storing electric energy in the form of kinetic
energy. The motor/generator works as a motor during storing energy to accelerate the flywheel
and as a generator during supplying energy to be driven by the flywheel.

 Bearings

Bearings are required to keep the rotor in place with very low friction, yet provide a support
mechanism for the flywheel. The bearing system can be mechanical or magnetic, depending
on the weight, life, and lower losses . Gas bearings cannot be used due to the vacuum within
the enclosure. Traditionally mechanical ball bearings have been used, but these have a higher
friction compared to magnetic bearings and also require higher maintenance as a result of
lubricant deterioration. These difficulties may be mitigated by using a hybrid system of
magnetic and mechanical bearings. A magnetic bearing has no friction losses and does not
require any lubrication but, if active, requires power to energize it. It stabilizes the flywheel
by supporting its weight using permanent magnets

 Power Conversion System

The power conversion/conditioning system usually has two converters (back-to-back

converter); one for the motor/generator and the other for the grid connecting by a common
DC link as shown in figure 4.2.
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 Figure 4.2 : Back-to-Back converter

When such a system is applied, a DC voltage can be rectified from an AC variable frequency
waveform; and an AC waveform can be created from a DC one with the required frequency
and voltage level. During discharge of FESS, the electric machine works as a generator
extracting mechanical energy from the flywheel and as a result the speed of the flywheel slows
down changing the frequency of the AC output. During charging period, the power
conversion/conditioning system draws the power from the grid to drive the electric machine
which works as a motor in this case. The DC link is used to support the voltage level while
charging and discharging.

 Housing

Housing is important for safety and improving FESS performance. The housing is a vessel or
an enclosure which surrounds the FESS components preventing any damages or injuries in
case of flywheel failure. To cope with the problem of air drag forces which increases the idling
losses of FESS, a vacuum enclosure is an optimum option and is depicted in figure 4.1.

4.1.2 COMPRESSED AIR ENERGY SYSTEM (CAES)

The energy storage stage of the CAES system is completed by the compressor, while the
power generation stage is completed by the expander and generator. The compressed air is
stored in the gas tank. The system diagram is shown in figure 4.3. When the power is rich, the
compressor is started. The air enters the compressor driven by the motor for compression, and
the high-pressure air is stored in the air tank. When the grid is short of power, compressed air
enters the expander, which drives the synchronous generator to generate electricity.

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 Figure 4.3 - Compressed air energy storage system : 1- Motor,2- Multistage compressor, 3 -
Compressed air tank,4- Multistage expander, 5- Generator, 6- Heat storage tank, 7- Cold storage
tank

4.2 PROPOSED SYSTEM

Figure 4.4 : Composite energy storage system

1-Dispatching device, 2- Data Acquisition Module, 3-Time Synchronization Module, 4 -
Frequency regulation module, 5- Peak regulation module, 6-Load forecasting module, 7 –FESS
8- CAES

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At off-peak hours and when energy is available, FES and CAES absorbs the power from grid.
The price of energy will also be less at that time. The data acquisition module collects the data
from grid. If the values doesn’t match the desired values, the storage system will give the power
back to grid and there will be a demand for power at that time which increases the price as well.

• FREQUENCY REGULATION (FES) : When power supplied is greater than load, frequency
increases and when power supplied is less than load, frequency decreases. If frequency varies,
the frequency regulation module calculates the power needed to compensate the variation and
drives FES in absorbing or generating mode.
• PEAK REGULATION (CAES) : At off-peak hours, the motor works and compress the air.
The air is compressed at different stages to improve efficiency of the system. During
compression, temperature rises, this heat is extracted and stored in heat storage tank which
can be used in expansion. The compressed air is stored in air storage tank. When peak time
arrives, i.e., when we need more power, the peak regulation module calculates the power
required and drives CAES in generation mode. The peak regulation module also receives the
time information from time synchronization module and load forecast value from load
forecast module. The time synchronization module sets the time and power value and, load
forecasting module having the forecasting data helps the system to work properly for next 15
minutes.
• PHASE MODULATION (CAES) : There are 2 separate valves; operation regulating and
phase regulating valve. Phase regulating valve is used for regulating phase value. It ensure the
expander temperature is under limit. The excitation system controls the generator to draw
leading current with over excitation and lagging current with under excitation.

Figure 4.5 :CAES with synchronous condenser

1- High-pressure gas storage tank, 2- Intake main air valve, 3- Operation regulating valve, 4-
Phase regulating valve, 5- Expander, 6-Generator, 7- Excitation device, 8-atmosphere

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  BLACKSTART (CAES) : When power system fails, the unit can work in the power grid
as blackstart power source. The inlet valve is opened and thus starts expanding, drives the
turbine and hence generator. The outlet switch is closed and then it power the grid.

Figure 4.6 : CAES with black start function

1-Air compressor, 2-Motor, 3-Gas storage tank, 4-Expander, 5-Generator, 6-Transformer,7 -
Station service bus, 8-atmosphere

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 CHAPTER 5
CHALLENGES

Though the system has many advantages discussed above, it face many challenges when it
reaches the ground reality. They are :

 High capital cost is required

 Large area is required for this setup
 Challenges in FES
 Challenges in CAES

Figure 5.1 : News on Beacon Plant explosion

(Courtesy : Times Union, New York)

The newspaper shows the explosion happened in Beacon’s Flywheel Energy Storage plant. Even
though it wasn’t a massive explosion, it brought them in back foot and affected them financially.
They came back strongly then. But, the credibility by natives have gone down.

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 Figure 5.2 : LightSail Energy

LightSail Energy was a company known for CAES failed to expand their business and their
mismanagent of money led them to financial crisis.

So the major challenge of these developing technologies is lack of financial management, less
efficient setup in large scale and promises given to investors couldn’t get fulfilled leading to crisis.
Another challenge is can renewables “replace” the existing power generation systems. Because
in Germany, they tried to replace them and was very expensive and couldn’t decrease the carbon
emissions as well. In contrast, France invested in nuclear energy instead of switching to
renewables, has very less carbon emissions and low energy cost (see appendix).

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 CHAPTER 6
CONCLUSION

Studied about the system proposed which performs power grid frequency regulation, peak
regulation, black start, and phase modulation. The paper concludes with the need for researches
in more efficient FES & CAES. The problems discussed in it need a comparative study in carbon
emissions, environmental impacts and cost of renewables including storage needs.
Comprehensive studies on all energy sources especially nuclear energy which is non – biased to
socio – political history.

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REFERENCES
[1] Wen, Xiankui, Jingliang Zhong, Jinzhao Tian, and Haoran Xiong (2020) , “ Research
on Fine Speed Adjustment of Expansion Power Generation System”, IEEE 5th Information
Technology and Mechatronics Engineering Conference (ITOEC), pp. 682-685.
[2] Amiryar, Mustafa E., and Keith R. Pullen (2017), “A review of flywheel energy storage
system technologies and their applications”, Applied Sciences 7, MDPI, no. 3 (2017): 286.
[3] Daoud, Mohamed I., A. S. Abdel-Khalik, A. Massoud, S. Ahmed, and Nabil H. Abbasy
(2012), “On the development of flywheel storage systems for power system applications: A
survey”, XXth International Conference on Electrical Machines, pp. 2119-2125. IEEE, 2012
[4] Mei, ShengWei, JunJie Wang, Fang Tian, LaiJun Chen, XiaoDai Xue, Qiang Lu, Yuan
Zhou, and XiaoXin Zhou (2015), “ Design and engineering implementation of non-
supplementary fired compressed air energy storage system: TICC-500”, Science China
Technological Sciences 58, no. 4 (2015): 600-611
[5] “Flywheels fail at energy project,” Times Union, 20-Oct-2011. [Online]. Available:
https://www.timesunion.com/local/article/Flywheels-fail-at-energy-project-2227225.php.
[Accessed: 22-Nov-2020].

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 APPENDIX

Clean energy contribution to total in France & Germany

Source : BP Energy Outlook, 2016

Electricity prices in EU countries

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