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Undoubtedly, energy has a significant role in economic growth and technical developments. Renewable energy resources are becoming more important in recent years due to their tremendous contributions to the independence of power generation industry from traditional fossil energy resources. Wind energy has been outstanding among renewable energy resources since continuous harvestable potential on the earth is approximately around 10 6 MW. Concerning the variable nature of wind energy, the variable speed machines, especially doubly fed induction generators (DFIG) are one of the considerations for wind energy conversion systems (WECS). Their implementation in renewable energy conversion systems is dramatically increasing due to their numerous advantages such as low cost and small size, the elimination of external DC source, the ability to produce maximum power under various wind and rotational speeds, the capability of controlling active and reactive power, and the opportunity to employ cheaper and smaller convertors and controllers. This paper is an extensive review of researches in the past 30 years on DFIG. The study starts with describing general perspective on wind energy and commonly used generators in wind conversion. Then it presents more details on DFIGs operational modes, utilizations, their modeling and simulation. It is followed by DFIG control methods and overviews of different employed electrical and mechanical controlling methods. Finally the review on the mutual impact of DFIG on power networks and vice versa, including wind uncertainty, power and frequency stability, power and voltage quality, operation under steady state, dynamic and fault conditions, and protections is given. Based on the review DFIG has advantages in terms of electrical, mechanical, and economic perspectives. It can be concluded that the DFIG has the most promising future for WECSs in power generation to complement the conventional systems. |
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