Abstract
The inherent differences between salient and nonsalient electrical machines are evaluated for two permanent magnet generators with different configurations. The neodymium based (NdFeB) permanent magnets (PMs) in a generator are substituted with ferrite magnets and the characteristics of the NdFeB generator and the ferrite generator are compared through FEM simulations. The NdFeB generator is a nonsalient generator, whereas the ferrite machine is a salient-pole generator, with small saliency. The two generators have almost identical properties at rated load operation. However, at overload the behaviour differs between the two generators. The salient-pole, ferrite generator has lower maximum torque than the NdFeB generator and a larger voltage drop at high current. It is concluded that, for applications where overload capability is important, saliency must be considered and the generator design adapted according to the behaviour at overload operation. Furthermore, if the maximum torque is the design criteria, additional PM mass will be required for the salient-pole machine.
Highlights
The material most commonly used as permanent magnets (PMs) in electrical machines is neodymium-iron-boron, Nd2Fe14B
The results presented here are from simulations using a two-dimensional model solved with the finite element method (FEM) [16]
The small saliency of the ferrite machine affects the shape of the torque curve and the overload capability even though the differences between the two machines are small; see (1) and (2)
Summary
The material most commonly used as permanent magnets (PMs) in electrical machines is neodymium-iron-boron, Nd2Fe14B (shortened as NdFeB). Several theoretical comparisons of generators with NdFeB and ferrites for wind power generators have previously been performed [2, 4,5,6]. In most of these studies [4,5,6] the better magnetic performance of NdFeB is used as an argument for its advantage. The behaviour of a permanent magnet synchronous generator (PMSG) with NdFeB at variable speed and load has been especially evaluated [9]. The intrinsic difference between these two generator types was not considered in [2]; that is, the difference in saliency which may affect the variable load operation and especially overload behaviour
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