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wind energy system control engineering design pdf

Preface
Harvesting energy on a global, sustainable, and economic scale is one of the major
challenges of this century.

With emerging markets, newly industrializing nations, and
shortage of existing resources, this problem will continue to grow.

Wind energy, in the
current scenario, is playing a central role, being the fastest-growing source of energy
worldwide in the last few decades.
However, long-term economic sustainability of wind energy is still to be achieved. This
would imperatively require improving critical engineering and economic practices to reduce
the cost of wind energy as compared to conventional energy to help increase its proliferation.
Wind turbines are complex systems, with large flexible structures working under very
turbulent and unpredictable environmental conditions.

Moreover, they are subject to a
variable and demanding electrical grid.

Their efficiency, cost, availability, and reliability
strongly depend on the applied control strategy.

As wind energy penetration in the grid
increases, additional challenges such as the response to grid voltage dips, active power
control and frequency regulation, reactive power control and voltage regulation, grid
damping, restoration of grid services after power outages, necessity of wind prediction,
etc., crop up.
Large nonlinear characteristics and high model uncertainty due to the interaction of
the aerodynamic, mechanical and electrical subsystems, stability problems, energyconversion efficiency, load reduction strategies, mechanical fatigue minimization problems, reliability issues, availability aspects, and cost reduction topics all impose the need
to design advanced control systems in a concurrent engineering approach.

This approach
coordinates many variables such as pitch, torque, power, rotor speed, yaw orientation,
temperatures, currents, voltages, power factors, etc.

It is a multidisciplinary task and must
be developed under the leadership of an experienced engineer.

In this book, we claim this
role for the control engineer, with the ultimate goal of achieving an optimum design, taking
into account all the aspects of the big picture of the new energy system.
Thus, the first objective of this book is to present the latest developments in the field
of applied control system analysis and design and to stimulate further research, including new advanced nonlinear multi-input multi-output robust control system design
techniques: quantitative feedback theory (QFT), and nonlinear switching strategies.

The second objective of this book is to bridge the gap between the advanced control theory and
the engineering application to design, optimize, and control wind energy systems.
The book is especially useful as it combines hard-to-find industrial knowledge of wind
turbines and the required control theory in a concise document from the perspective of
both a practicing and real-world engineer.

The wind turbine design standards and the
experimental results included in this book will be vital to anyone entering the industry.
The control portion of the book guides the reader through robust theories and reliable
ideas successfully applied to real multimegawatt wind turbines.
This book is divided into two parts.

Part I (Advanced Robust Control Techniques: QFT
and Nonlinear Switching) consists of seven chapters and presents concepts of nonlinear
multi-input multi-output robust control in such a way that students and practicing engineers can readily grasp the fundamentals and appreciate its transparency in bridging the gap
between theory and real–world applications.

Authors
Dr. Mario García-Sanz is an endowed chair professor at
Case Western Reserve University (CWRU), Ohio; the Milton
and Tamar Maltz professor in energy innovation; and director of the Control and Energy Systems Center at CWRU
(http://cesc.case.edu). As senior advisorto the president of the
M.Torres Group and as full professor at the Public University
of Navarra, he has played a centralrole in the design and field
experimentation of advanced multimegawatt wind turbines
forindustry leaders overthe lasttwo decades.

Dr. García-Sanz
held visiting professorships at the Control Systems Centre,
UMIST (United Kingdom, 1995); at Oxford University (United
Kingdom, 1996); at the Jet Propulsion Laboratory NASA-JPL
(California, 2004); and at the European Space Agency ESA-ESTEC (the Netherlands, 2008).
He holds 20 industrial patents, has done more than 40 large research projects for industry
and space agencies, and is the author or coauthor of more than 150 research papers, including
the books Quantitative Feedback Theory: Theory and Applications (Taylor & Francis, 2006) and
Wind Energy Systems: Control Engineering Design (Taylor & Francis, 2012).

Dr. García-Sanz is
subject editor of the International Journal of Robust and Nonlinear Control, is a member of IFAC
and IEEE technical committees (robust control, aerospace control), and has served as NATO/
RTO lecture series director and as guest editor of international journals (special issues on:
Robust Control, QFT Control, Wind Turbine Control, Spacecraft Control). He was awarded the
IEE Heaviside Prize (United Kingdom) in 1995 and the BBVA Research Award (Spain) in
2001.

Professor García-Sanz’s main research interest focuses on bridging the gap between
advanced control theory and applications, with special emphasis on energy innovation,
wind energy, space, water, environmental, and industrial applications.
Dr. Constantine H. Houpis is an emeritus professor at
the Air Force Institute of Technology (AFIT).

Prior to this,
he was a senior research associate emeritus at the Air Force
Research Laboratory, Wright-Patterson Air Force Base,
Ohio. Dr. Houpis is an IEEE life fellow and has served as a
NATO/RTO lecture series director several times.

For almost
two decades, he worked very closely with Professor Isaac
Horowitz at AFIT and at the Air Force Research Laboratory
on the fundamentals of quantitative feedback theory and
its applications to real-world projects, many of them in the
field of aerospace.

His textbook, Feedback Control System
Analysis and Synthesis (1960), coauthored with his colleague,
John J. D’Azzo, is recognized as a classic in its field.

This textbook and its sequel, Linear
Control System Analysis and Design—Conventional and Modern, have been translated
into several languages and have had seven editions.

Other well-known books written

Introduction

1.1 Broad Context and Motivation
With a capacity that has tripled in the last 5 years, wind energy is again the fastest growing
energy source in the world. Wind turbines (WTs) are used to collect kinetic energy and to
convert it into electricity.

The average power output of a WT unit has increased significantly in the last few years. Most major manufacturers have developed large turbines that
produce 1.5–5.0MW of power for onshore applications and are thinking of bigger units
for offshore projects.

Grouped together, they generate energy equaling 2% of the global
electricity consumption, with about 200GW of wind-powered generators worldwide by
the end of 2010.
Although wind energy is a clean and renewable source of electric power, many challenges still remain unaddressed.

WTs are complex machines with large flexible structures
working under turbulent, unpredictable, and sometimes extreme environmental weather
conditions, and are connected to a constantly varying electrical grid with changing voltages, frequency, power flow, and the like.

WTs have to adapt to these variations, so their
reliability, availability, and efficiency depend heavily on the control strategy applied. As wind
energy penetration in the grid increases, additional challenges are being revealed:response
to grid disturbances, active power control and frequency regulation, reactive power control and voltage regulation, grid damping, restoration of grid services after power outages,
and wind prediction, to name a few.
However, occasionally, you can still find very serious accidents, involving unstable situations and uncontrollable conditions, even in the largest machines and with the best international companies (see Figures 1.1 through 1.4).
With this very critical motivation, the authors claim for the need of a truly reliable control
design methodology! In their experience in designing commercial multimegawatt WTs, the
quantitative feedback theory (QFT) has been proved to be a reliable control engineering
technique successfully applied to many critical systems,151–187 including wind energy applications as seen in this book.
1.2 Concurrent Engineering: A Road Map for Energy
Control engineering plays a primary and centralrole in the design and development of new
challenging engineering systems.

In addition, bridging the gap between advanced control
theory and engineering real-world applications is the key factor in achieving breakthroughs

1.3 Quantitative Robust Control
Many of the frequency domain fundamentals were established by Hendrik W. Bode in his
original book Network Analysis and Feedback Amplifier Design,
1 published in 1945. It strongly
influenced the understanding of automatic control theory for many years, especially where
system sensitivity and feedback constraints were concerned.
But it was not until 1963 that a new book, Synthesis of Feedback Systems,
2 written by Isaac
Horowitz, showed a formal combination of the frequency methodology with plant ignorance considerations under quantitative analysis.

It addresses an extensive set of sensitivity problems in feedback control and was the first work in which a control problem was
treated quantitatively in a systematic way.

Any serious student of feedback control theory
must eventually first study Isaac’s book carefully.
Since then, and during the last decades of the twentieth century, there has been a tremendous advancement in robust frequency domain methods.

One of the main techniques,
also introduced by Horowitz, which characterizes closed loop performance specifications
against parametric and nonparametric plant uncertainty, mapped into open loop design
constraints, became known as QFT in the early 1970s.
3–187
QFT is an engineering control design methodology that explicitly emphasizes the use
of feedback to simultaneously and quantitatively reduce the effects of plant uncertainty
and satisfy performance specifications (see also the book by Houpis, Rasmussen, and
Garcia-Sanz).
6
QFT is deeply rooted in classical frequency response analysis involving Bode diagrams, template manipulations, and Nichols charts.

It relies on the observation that
the feedback is needed principally when the plant presents model uncertainty or when
there are uncertain disturbances acting on the plant.

Figure 1.6 describes the big picture
of QFT control system design, bridging the gap between control theory and real-world
applications.
151–187