147
Chapter 5
Doubly Fed Induction
Generators:
Overview and Intelligent Control Strategies
for Wind Energy Conversion Systems
Vinod Kumar
College of Technology and Engineering, India
Steven Kong
University of Queensland, Australia
Yateendra Mishra
University of Queensland, Australia
Z. Y. Dong
The Hong Kong Polytechnic University, Hong Kong
Ramesh. C. Bansal
University of Queensland, Australia
AbstrAct
Adjustable speed induction generators, especially the Doubly-Fed Induction Generators (DFIG) are
becoming increasingly popular due to its various advantages over fixed speed generator systems. A
DFIG in a wind turbine has ability to generate maximum power with varying rotational speed, ability
to control active and reactive by integration of electronic power converters such as the back-to-back
converter, low rotor power rating resulting in low cost converter components, etc, DFIG have become
very popular in large wind power conversion systems. This chapter presents an extensive literature
survey over past 25 years on the different aspects of DFIG. Application of H∞ Controller for enhanced
DFIG-WT performance in terms of robust stability and reference tracking to reduce mechanical stress
and vibrations is also demonstrated in the chapter.
DOI: 10.4018/978-1-60566-737-9.ch005
Copyright © 2010, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.
Doubly Fed Induction Generators
Figure 1. Main components of a wind turbine system (adapted from Chen and Blaabjerb, 2006)
1 IntroductIon
Modern power generation relies heavily on conventional power plants, which uses non-renewable sources.
The use of non-renewable sources such as coal and Nuclear can have adverse effect of on the environment by increased CO2 emissions and production and radioactive wastes. To ensure the preservation of
the environment and security of future electricity supply, many organizations have shifted their focus
towards renewable energy sources such as wind, solar, hydro, tidal wave, biomass, etc. Volatile fuel
prices used in conventional power systems are also one of the contributing factors for this change.
Historically, renewable energies have had limited industry investments, however one that has evolved
furthest is wind power technology. The Global Wind Energy Council (GWEC) states that wind energy
developments has occurred in more than 70 countries around the world, with an installed capacity of
74,223MW in 2006, which is an increase of 26% from 2005 to 2006 (Global Wind Energy Council,
2006).
In recent years, the application of Doubly-Fed Induction Generators (DFIG) in wind turbines has
gained significant interests and developments for its high power capacity and network support capabilities. A DFIG has the ability to generate maximum power with varying rotational speed ability to
independently control the active and the reactive power by the integration of electronic power converters
such as the back-to-back converters, low rotor power rating resulting in low cost converter components
and so on. However, the lack of experience and knowledge in grid integration of high levels of wind
power remains an issue to date. Considerable amount of research is still required to develop the detailed
understanding of the impact of wind power penetration levels and their operational limits on the overall
power system stability.
The proposed chapter presents an extensive literature survey over past 25 years on the different aspects of DFIG and control strategies. An advanced controller for the DFIG will also be introduced which
aims at improving the operational efficiency of DFIG wind turbine in terms of robust performance and
to suppress dynamic loads in terms of mechanical stress and vibrations.
2 generAtor overvIew
Wind technology has evolved over the years to today’s modern Wind Energy Conversion Systems
(WECS) as shown in Fig. 1 (Chen and Blaabjerb, 2006).
All wind turbine systems are comprised of the components as shown in the Fig. 1. It is just a matter
148
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