Review and Improvement of Several Optimal Intelligent Pitch Controllers and Estimator of WECS via Artificial Intelligent Approaches - Complex System Modelling and Control Through Intelligent Soft Computations - page 493

1 Introduction

Since 1985 wind power has improved essentially in European Union (EU) every
year growth at least 20 %. Wind power s natural popular of generating carbon-

emission free electricity ascribes increment, Wind Energy Conversion System
(WECS), this is the well-known growing method of new electrical generation in the
world (Boukhezzar et al. 2007 ). Wind energy increased very hasty through the
previous 25 years and became a significant branch of universal electrical power
supply. Progressively requirements for network connection of Wind Turbines and
Wind Farms were recognized by system operators in order to develop the grid
constancy.
In addition as we know the increase in the average temperature of the Earth

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s
near-surface air and oceans is a major issue all over the world. In accordance with
the Intergovernmental Panel on Climate Change (IPCC) the mainstream of the
temperature increase is caused by the greenhouse effect (Verdonschot 2009 ).
The greenhouse effect refers to the change in steady state temperature of a planet
by the presence of an atmosphere containing gas that absorbs and emits infrared
radiation. More than seventy

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five percent of the greenhouse gas releases on earth are
caused by the combustion of fossil fuels. Wind power, solar power, hydropower and
biomass and other renewable energy technologies can decrease the production of
greenhouse gases extensively and at the same time reduce the addiction on the oil
industry. These two point of view combined make renewable energy a major item
all over the world. Wind power is the fastest growing renewable energy source.
Wind power is presently responsible for about 1.5 % of the world ' is electricity use

(Kanellos et al. 2000 ).
Due to this high interest in wind energy, it becomes to a greater extent important
to increase the ef ciency of wind energy conversion systems (WECS), also called

wind turbines. Wind turbines extract kinetic energy from the wind and convert this
into mechanical energy. This mechanical energy is then converted to electrical
energy by means of a generator. The maximum amount of energy from the wind is
extracted using wind turbine when it operates at an optimal rotor speed. Optimal
operation of rotor depends on the wind speed. Because the wind speed is variable
by nature, the optimal rotor speed also varies. Earlier research has shown that
variable speed operation of the rotor results in a higher energy production compared
to a system operating at one constant speed. Beside an increase in energy pro-
duction, variable speed operation enables a reduction in dynamic loads acting on
the mechanical components (Kanellos et al. 2000 ; Carlin et al. 2001 ; Mangialardi
and Mantriota 1996 ; Cotrell 2004 ). On the other hand, a problem arises when the
speed of the rotor varies while the wind turbine must deliver AC power with a

xed
phase and frequency to the electrical grid. To match the grid requirements, current
variable speed wind turbines incorporate expensive power electronics to convert the
variable frequency power to a constant frequency (Verdonschot 2009 ).
The power electronics contain a partial ef

ciency and they can introduce har-
monic distortion of the AC current in the electrical grid, reducing the quality of the