6Lai L L, Chan T F. Distributed generation: induction and permanent magnet generators[M]. New York: John Wiley and Sons, 2007.
7Polinder H, van der Pigt F F A, Gert-Jan de Vilder, et al. Comparison of direct-drive and geared generator concepts for wind turbines[J]. IEEE Transactions on Energy Conversion, 2006, 21(3): 725-733.
8Ribrant J, Bertling L M. Survey of failures in wind power systems with focus on Swedish wind power plants during 1997-2005[J]. IEEE Transaction on Energy Conversion, 2007, 22(1): 167-173.