Comparative advantage of flux switching PM machines for medium-speed wind drives

Wind turbine manufacturers are growing more interested in harnessing the potentials in medium-speed drivetrains as against low-speed (gearless) and the well-established high-speed drivetrains. The main concerns are the low downtime in gearbox systems, the high cost of PM and difficult logistics necessitated by the increasing mass of existing wind systems, especially at higher megawatts (MW). Already, conventional wind generators have been tested in the medium-speed drivetrains even though they are not fully developed. In other cases, it has been shown that medium-speed wind drive is a good compromise compared to high-speed and gearless systems. However, such prospects remain to be demonstrated for the re-emerging flux switching permanent magnet (FSPM) brushless machines. In this paper, an attempt to compare different FSPM machines by using finite-element analysis indicates that medium-speed drivetrains could provide salient advantages like reduced total losses, high efficiency, low cogging torque and better torque factor. This means that the overall economics of the wind turbine may be improved.