**1. Renewable energy sources**

Energy is essential for the growth and socio-economic development of any economy. Recently, the use of renewable energy sources for energy generation is on the raise. Wind energy is one of the renewable energy sources that is indigenous in nature and could help in mitigating fossil fuels dependency [1]. Presently, about 87% of total energy in the world is obtained from traditional fossil fuels (coal, oil and natural gas), while 6% is obtained from nuclear plants and the remaining 7% is generated from renewable sources (especially hydropower, wind and solar) [2]. Unfortunately, the amounts of fossil fuel and nuclear power resources are limited. Based on the current estimates given in the literature, natural uranium used for nuclear power technology will last only about 50 years; oil, no more than 100 years; natural gas, 150 years; and coal, 200 years.

Due to the fact that fossil and nuclear fuels are highly depended upon for energy generation, there are environmental pollution and safety challenges, which are now becoming dominant issues in the society and international world. Recently, there was a Paris climate agreement in France. "The agreement is within the United Nations Framework Convention on Climate Change (UNFCCC), dealing with greenhouse gas emissions mitigation, adaptation and finance, commencing in the year 2020" [3, 4]. The terms of the agreement was deliberated by 196 representatives during the 21st Conference of the UNFCCC in Paris and on December 12, 2015, it was adopted by consensus. The world is drastically focusing on clean and safe renewable energy sources due to the effects of environmental pollution on global warming. In the long run, the resulting change of climate has disastrous consequences on the planet.

There are enormous resources of wind energy, and it has been estimated in the literature that if 10% of the wind energy could be barely tapped, the electricity needs of the world could be

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

supplied [2, 5]. With the recent advancement of variable speed wind turbines, power electronics, drives and control system technologies, wind energy is now competitive with traditional coal and natural gas power. However, one of the shortcomings of wind energy is that it is stochastic in nature, thus making its availability sporadic, consequently, needs back up by other conventional power sources.

Wind power generation has an edge over the other renewable energy technologies application, because of its technological maturity, good infrastructure and relative cost competitiveness. In the near future, wind energy is expected to play a vital role in both national and international levels regarding energy scenarios [1, 5, 14]. Basically the kinetic energy of the wind is converted to electrical energy via the wind turbine blades rotation. According to Greenpeace report in the literature, by the year 2020, about 10% electricity in the world can be obtained by the wind energy. However, wind power is already competitive with conventional fossil fuel power stations at good windy sites. With this enhanced and mature wind technology, together with superior economics, experts predict wind power would capture 5% of the world energy market by 2020. Advanced wind turbines must be more reliable, efficient,

Introductory Chapter: Stability Control and Reliable Performance of Wind Turbines

http://dx.doi.org/10.5772/intechopen.80237

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There are three main types of wind turbines used nowadays [15]: the Fixed Speed Wind Turbines with Squirrel-Cage Induction Generator (FSWT SCIG), the Variable Speed Wind Turbines with Doubly Fed Induction Generator (VSWT DFIG) and the Variable Speed Wind Turbines with Permanent Magnet Synchronous Generator (VSWT PMSG). Wind energy technology has experienced important improvement in several last decades [16] due to the technological improvement of wind turbines from fixed speed to variable speed. A brief distinction of the three types

The SCIG are used in general as fixed speed wind turbine generators due to their superior characteristics such as brushless and rugged construction, low cost, maintenance free and operational simplicity. However, this type of wind turbine technology requires large reactive power to recover the air gap flux when a short circuit fault occurs or grid disturbances in the power system. SCIG wind turbine technology has limited ability to provide voltage and frequency control, except it is supported with some expensive external power electronic control

The variable speed turbines are becoming the norm for new wind farm installations, because of high energy capture efficiency couple with reduced drive train stresses [17]. The PMSG VSWT, also known as the direct-drive synchronous generator with permanent magnet excitation and the DFIG VSWT with doubly fed back-to-back power converter type technologies, have become the two generator alternatives. The former has the disadvantage of cost mainly due to a power converter rated for the full power. Although in the latter, a gear box is needed, the DFIG requires a converter of only 20–30% of the generator rating for an operating speed

Although the DFIG is not as rugged and robust as the squirrel-cage wind turbine type, however, the brushes have little wear and sparking when compared to DC machines and is the only acceptable option for alternative energy conversion in the megawatts power range. With the help of modern power electronic devices, it is possible to recover the slip power

robust and less expensive than current wind turbines.

of wind turbine driven generators is given below.

strategy, hence not commonly used in modern wind turbines.

range of 0.7–1.3 per unit (p.u) resulting in a lower cost.

**3. Wind turbine technology**

The solar photovoltaic systems have the merit of being static and require less repair and maintenance. However, it is five times more expensive than wind power, although recently, there is huge research and development to produce low cost photovoltaic solar panels for widespread applications. Solar power conversion performance efficiency is basically 16%, and its availability is also sporadic like the wind power.

Hydrogen gas is the primary fuel for fuel cell energy or a fossil fuel type like gasoline or methanol, with a reformer. Fuel cells are static and have high conversion efficiency of about 60% compared to wind and solar power. However, fuel cells are heavy, expensive and possess poor transient response in their current state. Although, fuel cells show tremendous promise for the future, especially for electric cars, however, a tremendous amount of research and development is needed to achieve this aim.
