wind energy systems solutions for power quality and stabilization pdf

Preface
This book provides fundamental concepts of wind energy conversion
systems and discusses grid integration and stability issues, methods
of transient stability enhancement and minimization of fluctuations of
power, and frequency and voltage of wind generator systems. Recently,
electricity generation using wind power has received much attention all
over the world.

Wind energy is a free, renewable resource, so no matter
how much is used today there will still be the same supply in the future.
Wind energy is also a source of clean, nonpolluting electricity.

Unlike conventional power plants, wind plants emit no air pollutants or greenhouse
gases.
Induction machines are mostly used as wind generators.

However,
induction generators have stability problems similar to the transient stability of synchronous machines. During a fault in the power network,
rotor speed of the wind generator goes very high, active power output
goes very low, and terminal voltage goes low or collapses down. Usually
the wind generator is shut down during these emergency situations.
Recent tradition is not to shut down the wind generator during a network
fault but to keep it connected to the grid through appropriate control.

This
clearly indicates that wind generator stabilization is necessary during network faults. Again, even though there is no fault in the network, due to
random wind speed variations, output power, frequency, and terminal
voltage of wind generators fluctuate.

However, consumers desire to have
constant voltage and frequency. Therefore, some control means are necessary to minimize power, frequency, and voltage fluctuations.

This book
discusses several means to enhance the transient stability of wind generator system and also explains the methodologies for minimizing fluctuations of power, frequency, and voltage.
The book is organized as follows.

Chapter 1 provides a general overview of wind energy and outlines the background, aim, and scope of
the book.

Chapter 2 describes the fundamental concept of wind energy
conversion systems and modeling of wind turbines.

Electric machines—
in particular induction machines and synchronous machines—are the
key to wind energy conversion systems. Therefore, the basic concepts of

electrical machines are discussed in Chapter 3.

With the variable-speed
wind generator system, the terminal of the generator is connected to the
grid through a power electronics interface.

Also, to integrate the energy
storage system into the wind generator system, power electronics is necessary.

Thus, Chapter 4 deals with a brief overview and fundamental concepts of power electronics devices. The types of wind generator systems
are discussed in Chapter 5.
Chapter 6 discusses the grid integration issues of wind generator systems.

In particular, the transient stability issue, power quality problem,
fluctuations of power, frequency, and voltage of wind generator systems
during random wind speed variations are described.

Chapter 7 analyzes
the solutions for power quality issues of wind generator systems, especially minimization of fluctuations of power, voltage, and frequency of
wind generators during random wind speed variations by energy storage devices.

Chapter 8 describes the various methods of transient stability enhancement of wind generator systems during network faults.
Simulation results are provided to demonstrate the effectiveness of the
stabilization methods.

Comparisons among the stabilization methods are
made on the basis of performance, control structure, and cost.

Chapter 9
deals with the fault-ride through capability and mitigation of power fluctuations of variable-speed wind generator systems, especially for doubly fed induction generator systems, wound-field synchronous generator
systems, and permanent magnet synchronous generator systems.

About the Author
Mohd. Hasan Ali received a BScEng in electrical and electronic engineering from Rajshahi University of Engineering and Technology (RUET),
Rajshahi, Bangladesh, in 1995, and an MScEng and PhD in electrical and
electronic engineering from Kitami Institute of Technology, Kitami, Japan,
in 2001 and 2004, respectively.

He was a lecturer from 1995 to 2004 and
assistant professor in 2004 in the Department of Electrical and Electronic
Engineering at RUET. He was a postdoctoral research fellow at the Kitami
Institute of Technology, Japan, under the Japan Society for the Promotion
of Science (JSPS) Program from November 2004 to January 2007.

He was
also a research professor with the Department of Electrical Engineering
at the Changwon National University, South Korea, during 2007. Ali
served as postdoctoral research fellow with the Department of Electrical
and Computer Engineering at Ryerson University, Canada, from 2008 to
2009. From 2009 to 2011 he was a faculty member with the Department of
Electrical Engineering at the University of South Carolina.

Currently, he is
an assistant professor at the electrical and computer engineering department of the University of Memphis, Tennessee.

Overview
The terms wind energy and wind power describe the process by which
the wind is used to generate mechanical power or electricity.

Wind turbines convert the kinetic energy in the wind into mechanical power.

This mechanical power can be used for specific tasks (e.g., grinding grain or
pumping water), or a generator can convert this mechanical power into
electricity to power homes, businesses, schools, and the like.

Recently, generation of electricity using wind power has received much attention all
over the world. This chapter provides an overview of wind energy systems.
1.1 Introduction
Wind energy is a free, renewable resource, so no matter how much is used
today there will still be the same supply in the future. Wind energy is
also a source of clean, nonpolluting electricity.

Unlike conventional power
plants, wind plants emit no air pollutants or greenhouse gases.

Currently,
extensive research on wind energy is going on in various countries of
the world, including the United States, Germany, Spain, Denmark, Japan,
South Korea, Canada, Australia, and India. There are several organizations for wind energy research in the world, like the Global Wind Energy
Council (GWEC), National Renewable Energy Laboratory (NREL), and
American Wind Energy Association (AWEA).

According to a GWEC
report [1], about 12% of the world’s total electricity demand can be supplied by the wind energy by 2020.

This figure indicates the importance of
wind energy research these days.
1.2 Why Renewable Energy
Coal, oil, and gas, which are being used as fuels for conventional power
plants, are being depleted gradually, so exploration of alternative fuel
sources—that is, renewable energy sources for producing electricity—is
needed.

There are various types of renewable energy sources, like solar
energy, wind energy, geothermal, and biomass.

Renewable energy is the
use of nonconventional energy sources to generate electrical power and
fuel vehicles for today’s residential, commercial, institutional, and industrial energy applications.

This includes emergency power systems, transportation systems, on-site electricity generation, uninterrupted power
supply, combined heat and power systems, off-grid power systems, electrical peak-shaving systems, and many more innovative applications.

2 Wind Energy Systems: Solutions for Power Quality and Stabilization
Wind power has a great advantage over conventional fuels. Its operation does not produce harmful emissions or any hazardous waste.

It does
not deplete natural resources in the way that fossil fuels do, nor does it
cause environmental damage through resource extraction, transport, and
waste management.
The generation of electricity by wind turbines is dependent on the
strength of the wind at any given moment.

Wind farm sites are chosen
after careful analysis to determine the pattern of the wind—its relative
strength and direction at different times of the day and year. So wind
power is variable but not unpredictable.
1.3 Wind Energy
Wind power or wind energy is the process by which the wind is used to
generate mechanical power or electrical power and is one of the fastestgrowing forms of electrical power generation in the world.

The power of
the wind has been used for at least 3,000 years.

Until the twentieth century, wind power was used to provide mechanical power to pump water
or to grind grain.

At the beginning of modern industrialization, the use of
the fluctuating wind energy resource was substituted by fossil-fuel-fired
engines or the electrical grid, which provided a more consistent power
source. So the use of wind energy is divided into two parts: (1) mechanical
power generation; and (2) electrical power generation.
Wind is simple air in motion.

It is caused by the uneven heating of
the earth’s surface by the sun.

Since the earth’s surface is made of very
different types of land and water, it absorbs the sun’s heat at different
rates. During the day, the air above the land heats up more quickly than
the air over water.

The warm air over the land expands and rises, and the
heavier, cooler air rushes in to take its place, creating winds.

At night, the
winds are reversed because the air cools more rapidly over land than over
water. In the same way, the large atmospheric winds that circle the earth
are created because the land near the earth’s equator is heated more by the
sun than the land near the North and South Poles.
Today, wind energy is mainly used to generate electricity. Wind is
called a renewable energy source because the wind will blow as long as
the sun shines.

1.4 Advantages and Disadvantages
of Wind-Generated Electricity
1.4.1 A Renewable Nonpolluting Resource
Wind energy is a clean, reliable cost effective source of electricity.
Electricity generated from the wind does not contribute to global

warming and acid rain.

Compared to energy from nuclear power plants,
there is no risk of radioactive exposure from wind power.
1.4.2 Cost Issues
Even though the cost of wind power has decreased dramatically in the
past 10 years, the technology requires a higher initial investment than
fossil-fueled generators. Roughly 80% of the cost is the machinery, with
the balance being site preparation and installation.

If wind-generating
systems are compared with fossil-fueled systems on a “life-cycle” cost
basis (counting fuel and operating expenses for the life of the generator),
however, wind costs are much more competitive with other generating
technologies because there is no fuel to purchase and minimal operating
expenses.
1.4.3 Environmental Concerns
Although wind power plants have relatively little impact on the environment compared with fossil fuel power plants, there is some concern over
the noise produced by the rotor blades, aesthetic (visual) impact, and the
death of birds and bats caused from flying into the rotors. Most of these
problems have been resolved or greatly reduced through technological
development or by properly siting wind plants.
1.4.4 Supply and Transport Issues
The major challenge to using wind as a source of power is that it is intermittent and does not always blow when electricity is needed. Wind
cannot be stored (although wind-generated electricity can be stored if batteries are used), and not all winds can be harnessed to meet the timing of
electricity demands.

Further, good wind sites are often located in remote
locations far from areas of electric power demand (such as cities). Finally,
wind resource development may compete with other uses for the land,
and those alternative uses may be more highly valued than electricity
generation. However, wind turbines can be located on land that is also
used for grazing or even farming.
1.5 Worldwide Status of Wind Energy
The following provides an overview of the worldwide status of wind
energy based on the GWEC report [1]