Preface

Nowadays, intensive research and collaborative projects dealing with the installation of large wind turbines are taking place in many countries. The goal of this work is the decarbonization of electricity grid systems through the exploitation of wind power. In this context, modern and larger offshore wind turbines with power capacity reaching 15 MW and rotors of more than 230 meters in diameter are under continuous development to minimize the unit cost of energy production.

This book presents research in wind turbine design, manufacture, and operation. Its main topics include basic aspects of wind turbine design, low-specific power turbines, offshore wind industry and floating wind turbines, wind measurement and forecasting models, design and manufacturing of rotor blades, manufacture of power transmission bearings, and challenges in control strategies and computational aerodynamics.

Chapter 1 outlines the major design aspects of wind turbines. It analyzes the main structures to build a general optimization model. It defines and measures the most significant design objectives as well as design environment and constraints. It also identifies and discusses all effective system design variables and parameters. Several design alternatives are considered to see how the various design criteria are affected in each case.

Chapter 2 describes wind turbine generator protection based on fault current and voltage analysis, which can identify the instantaneous operation, delay operation, or immune operation. The fault scenarios are explained using simulation results on the wind turbine generator system modeled in a software environment.

Chapter 3 discusses the technological advantages provided by the low specific power (SP) turbine synthesized close to a target SP of 100 W/m2, which was determined by ground-based measurements. The findings imply that low-specific power wind turbines can improve the capacity utilization factor, lower the cost of energy, boost the value of wind, and better utilize the transmission system in all wind situations, albeit at varying magnitudes, according to the given results.

Chapters 4–9 focus on offshore wind farms, which are forecast to reach power capacity near 1000 GW by 2050 and will be a crucial part of the transition to net-zero emission. Chapter 4 gives insight into the forthcoming challenges and highlights potential solutions to make wind farms more self-reliant. It is concluded that the advent of a new class of converter-based power modules viz. grid forming will support the stability of offshore wind power plants and provide the needed services to ensure reliable and secure operation of future decarbonized electric networks.

Chapter 5 describes a new method for operating an offshore wind farm (OWF) with a diode-rectifier unit (DRU). A phase shifting transformer (PST) is applied on the onshore side of the medium-voltage submarine cable to avoid uncontrolled current flow through the cable. The application of PST is to ensure the smooth black-start and stable operation of the OWF and DRU-HVDC links. Both static and dynamic behaviours of the proposed method are presented, and the simulation results validate the given mathematical model.

Chapter 6 deals with the optimization of a crew transfer vessel (CTV) against an offshore wind turbine. It presents a proposal for improving the CTV by promoting the use of surface effect ships (SES) to minimize their heave under the constraint of fuel consumption. The study shows that another possible axis of development would be to design an additional wall to existing boat landings, providing sheltered water.

Chapter 7 discusses the prediction of sound pressure levels from a wind farm. The main characteristics are taking into account atmospheric stability to determine the acoustic power of the wind turbines; describing the generation of noise along the blades due to turbulent phenomena; and calculating the noise propagation at different distances from the tower taking into account atmospheric absorption, turbulence energy dissipation, and geometric divergence.

Chapter 8 addresses the different models for wind power forecasting, which is becoming increasingly significant due to the high penetration of wind power in the energy grid. Two main groups related to wind speed prediction are considered. The first group is based upon analysis of historical time series of wind, and the second uses forecasted values from a numerical weather prediction (NWP) model as an input. It is concluded that future research should focus on the following areas: implementation of artificial intelligence approaches to increase forecast accuracy; new strategies dealing with complicated terrain; more research into hybrid methods to combine physical and statistical approaches for achieving good results in both long-term and short-term prediction; and additional research into NWP models designed for use in an offshore environment.

Chapter 9 presents a droop-fed direct power control strategy in the variable speed pumped storage (VSPS) of a wind farm grid integration system. Modeling of the system is carried out based on the phasor model technique. The frequency spectrum analysis approach is used in the VSPS system for determining the dynamic performances of the grid in case of wind power fluctuation compensation and contingencies and validated in the MATLAB/Simulink platform. Results show that the frequency spectrum analysis method is effective for determining the wind power fluctuation and stability requirement in the large power system.

Chapter 10 focuses on the influences of the integration of wind power generators into power grid systems. The rotor side converter controller is used for active and reactive power control by controlling rotor current and the speed control of the Doubly Fed Induction Generator (DFIG). The control scheme and the simulation mode controller employed for the study assure the wind generator supplying the grid at varying wind speeds behaves like a synchronous generator at a 0 Hz rotor frequency.

Chapter 11 presents the fundamentals of wind turbine aerodynamics and the related terminologies to the design of blades. It discusses the three-dimensional computational aerodynamics of the blades as well as the design of vortex generators as an effective passive control device for airflow. The optimum dimensions and arrangement of these devices along the blade span are also studied aiming at the increase of the power output. It is concluded that integrating vortex generators in wind turbines is the next giant leap in aerodynamic research.

Chapter 12 discusses some techniques for the design and manufacturing of wind turbine blades, including the appropriate selection of the airfoil type, the design optimization methods, and manufacturing techniques. It highlights the superiority of using chord-wise and span-wise stiffeners to increase the stiffness of the skin of carbon fiber wind turbine blades. These stiffeners are not bonded externally to the skin, but rather they are layers of carbon fibers that are buried inside the skin of the wind turbine blades.

Chapter 13 describes the author's experience of a lifetime of casting metals and how the casting technique relates to the quality of the metal and offers answers to engineering failures. It is a concern that the failure of wind turbine bearings continues, on occasions, to defy substantial metallurgical efforts. It is proposed that there is good reason to identify the casting process as the generator of pervasive defects, which the author calls bifilms. These defects originate from the casting process during the pouring of the liquid steel. They exist in finished steel components as a substantial population of cracks. These pre-existing cracks are usually the initiators of fatigue failure as well as other failure modes.

Chapter 14 discusses wind turbine characteristics to design low-power rating generators, which is necessary for remote and rural electrification. The generator specifications have been obtained from wind turbine models such as torque, speed, and power. The rotor design reducing q-axis inductance of this generator is analyzed and the relationship between generated EMF voltage and torque with the change of time is evaluated. The effects of stator resistance on electromagnetic torque with a variation of power angle are also considered.

Chapter 15 discusses the optimization of operational safety and efficiency of wind energy conversion equipment. The proposed method involves flat blades or space prisms that perform translation motion due to the interaction with airflow. Theoretical results obtained are used in the design of new devices for energy extraction from airflow. Models of wind energy conversion devices equipped with one vibrating blade are developed (quasi-translatory blade's motion model; model with vibrating blade equipped with crank mechanism). Operation of the system due to the action of airflow is simulated with computer programs. Possibilities to obtain energy with generators of different characteristics, using mechatronic control, have been studied. The effect of wind flow with a constant speed and with a harmonic or polyharmonic component is considered.

Finally, it is a great pleasure for me to take this opportunity to express my gratitude and thanks to all the contributing authors. I also wish to express my gratitude for the help and support of the staff at IntechOpen, particularly Author Service Manager Ms. Elena Vračarić.

#### **Karam Maalawi**

**Chapter 1**

Wind Turbines

tion to the future energy needs.

affected in each case.

cations such as:

**2. System definition and main function**

*Karam Maalawi*

**1. Introduction**

Introductory Chapter: General

Design Aspects of Horizontal-Axis

Numerous research contributions in developing wind industry technologies worldwide have been initiated since the oil crisis in 1973, and various configurations of wind turbines and large-scale wind farms have been installed in many places. These clean energy sources can make a substantial and economically competitive contribu-

Irrespective of the specific application, a wind turbine system design should be based on the cost-effective production of energy. The main objective should be based on the minimum cost of energy depending on the rotor diameter, rated power as well as the wind characteristics for a given site. The economic feasibility of large-scale wind turbines operated as a part of electrical power systems has been considered by H. M. Bae [1]. In this paper, the design variables were taken to be the rotor diameter, rated power, and number of the installed machines. Maximization of the total net value of the generated power, which is equal to the annual expected fuel cost savings minus the total cost of the system, was taken as the main system objective. Power was considered as constraint rather than design objective. Hansen [2] addressed optimum blade shapes for maximizing the power coefficient of the rotor. He presented a method to obtain the optimum blade chord and twist distributions for better aerodynamic performance. Another important consideration in the design of wind energy generator systems is to reduce vibration without increasing structural weight. This is because the economics require that large wind turbines operate reliably for long

In this chapter, the wind turbine will be analyzed as a system in order to build a general model for its structural design optimization. The most significant design objectives as well as design environment and constraints are defined and measured. All effective system design variables and parameters are identified and discussed. Several design alternatives will be considered to see how the various design criteria are

A wind turbine can be defined as a device that converts the wind's kinetic energy into useful mechanical power. This produced power can be exploited in many appli-

periods of time while subject to significant vibratory loads [3, 4].

Professor of Aeronautics and Mechanics, Department of Mechanical Engineering, Institute of Engineering Research and Renewable Energy, National Research Centre, Cairo, Egypt
