Brushless Excitation Technolgies for Doubly Fed Induction Generator System: Survey of Solutions and Future Trends

The doubly-fed induction generator (DFIG) and the permanent magnet synchronous generator (PMSG) are the two popular generators for modern large-scale wind turbines. Compared with the traditional DFIG, the PMSG is favourable in offshore wind farms due to its advantages of brushless, high efficiency, and high power density. However, the high cost of power electronics and limited rare-earth reserves in PMSG could make the DFIG a rival alternative, especially in future large-scale wind turbines reaching 15 MW or 20 MW. This paper presents the DFIG system excitation technologies existing in the prevailing literature. Additionally, the pros and cons of DFIG system traditional excitation and recently developed brushless excitation technologies are presented. Furthermore, the latest developments in the excitation technologies for the DFIG system are introduced. Finally, the future trends of the excitation technologies for the large-scale DFIG system are put forward.