Page 265 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

252 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
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to the utility via net metering or a contract. Utilities on the other hand might be motivated in dealing
with those small prosumers willing to postpone their grid reinforcement infrastructure investments
or displacing reactive power required hardware or improving power factor in certain zones of the
distribution grid. Therefore, it is very important to understand the technology and economic basis
for small wind-based power systems.
In order to understand how to design a small wind power system, it is initially necessary to assess
(on an hourly basis) the typical load flow in the installation and all sources of energy that must meet
an average energy balance. Then, storage compensation may have to provide the instantaneous
power balance, typically a battery is used for such instantaneous compensation or a connection to
the utility grid. In parallel, other devices may have longer time needs, such as a photovoltaic power
system, pumped hydro, compressed air, diesel generator, or fuel cell. There are several other param-
eters to consider: how the power quality impacts the overall performance, how the system protection
requirement for islanding and reconnection is, how integrated must the battery and inverter control-
lers be, and how the electromechanical protections against strong and unsafe wind speeds are. It is
necessary to understand how the performance is affected by local conditions, that is, the random
nature of the wind, nearby obstructions, power-demand profiles, turbine-related factors, and dete-
rioration due to aging.
The objective of this chapter is to provide some understanding of a few important topics for
designing a small wind power system with a tutorial-like educational approach in the control and
design characteristics for small wind energy projects. The topics discussed in this chapter are
concerned with wind turbine components and their characteristics, typical wind turbine generators,
and the overall wind energy design. There is an example of an energy study with understanding of
the wind turbine control, explaining both mechanical and electrical aspects.

10.2 WIND TURBINE COMPONENTS

Wind turbines are categorized based on the orientation of their spin axis into horizontal-axis
wind turbines (HAWT) and vertical-axis wind turbines (VAWT) [1]. VAWT have their rotor shaft
transverse to the wind (but not necessarily vertical), and the main components are located at the
base of the turbine; that is, the generator and gearbox are located close to the ground, facilitating
service and repair. VAWT capture wind from any direction without being pointed towards the
main wind direction. Typical designs such as Savonius, Darrieus, and Giromill have significant
torque variation during each revolution causing bending moments on the blades with consequent
mechanical stress and material fatigue. VAWT have been studied and deployed in the past few
years, but the recent commercial success of wind turbines is really due to HAWT. Figure 10.1
shows the typical wind turbine components in a HAWT. There are three categories of components:
mechanical, electrical, and control. The following is a brief description of the main components:

• Tower is the physical structure that holds the wind turbine. It supports the rotor, nacelle,
blades, and other wind turbine equipment. Typical commercial wind towers are usually
50–120 m long and they are constructed from concrete or reinforced steel.
• Blades are physical structures, which are aerodynamically optimized to help capture the
maximum power from the wind in normal operation with a wind speed in the range of about
3–15 m/s. Each blade is usually 20 m or more in length, depending on the power level.
• Nacelle is the enclosure of the wind turbine generator, gearbox, and internal equipment. It
protects the turbine’s internal components from the surrounding environment.
• Rotor is the rotating part of the wind turbine. It transfers the energy in the wind to the shaft.
The rotor hub holds the wind turbine blades while connected to the gearbox via the low-
speed shaft.
• Pitch is the mechanism of adjusting the angle of attack of the rotor blades. Blades are turned
in their longitudinal axis to change the angle of attack according to the wind directions.