Abstract
Recently, the large-scale wind turbine market has expanded from onshore to offshore. Under the circumstances, to respond to requirements related to downsizing and weight reduction for the on-board generator, a permanent magnet type synchronous generator has been used. Because the offshore wind turbine drive train is difficult to maintain and so reliability is critical, a direct drive generator as well as a medium-speed generator with a low ratio gear are proposed for the drive train. With such a generator design, consequently, we have to investigate the number of poles and the winding method required to respond to the drive train type. In this study, we design a permanent-magnet type-synchronous generator for the medium-speed-type drive train, where we decide to employ the fractional slot winding method for high efficiency and low total harmonic distortion performance. We conclude that the optimum number of slots per pole per phase q is in the range 1 < q < 3/2. This is confirmed by experiments using a 2.2MW, 18min-1 test machine.
