Permanent magnet motors with rare earth magnets are amongst the best candidates for high performance applications such as automotive. However, due to their cost and risks relating to security of supply, alternative solutions such as ferrite magnets have recently become popular. In this paper the two major design challenges of using ferrite magnets for a high torque density and high speed application, namely their low remanent flux density and low coercivity, are addressed. It is shown that a spoke type design utilizing a distributed winding may overcome the torque density challenge due to a simultaneous flux concentration and reluctance torque possibility. Furthermore, the demagnetization challenge can be overcome through careful optimization of the rotor structure, with the inclusion of non-magnetic voids on the top and bottom of the magnets. To meet the challenges of the high speed operation an extensive rotor structural analysis has been undertaken, during which electro-magnetics as well as manufacturing tolerances are taken into account. The electromagnetic studies are validated through testing of a prototype, custom built for static torque and demagnetization evaluation. The disclosed motor design surpasses the state of the art performance and cost, merging the theories into a multi-disciplinary product.
Interior permanent magnet motors with ferrite magnets and distributed windings can be a cost effective alternative to rare-earth magnet based motors for demanding applications such as automotive traction. Among different rotor topologies, the spoke type may be preferred, due to its advantages for high flux concentration and resistance to demagnetization, when carefully designed. When high speed operation is required, to increase the power density of the motor, the spoke type rotor must comprise of two sections: a) the ferromagnetic rotor pole to provide the path for the magnetic flux, and b) the non-magnetic rotor support to provide the structural integrity. In this paper, the multiphysics and cost implications of the rotor support material, as part of a high performance ferrite magnet traction motor, are analyzed, and an optimal selection with respect to those criteria is proposed. The performance of the design based on the proposed rotor support material is validated by electromagnetic and structural testing of three sets of customized prototypes. Based on the analysis, the proposed rotor support material may, significantly, boost the cost competitiveness of a low cost ferrite motor for high volume production.
Permanent magnet motors with ferrite magnets may be applicable to demanding electric vehicle (EV) applications, provided that designs with high power density and efficiency, as well as high resistance to demagnetization are developed. One rotor topology that allows meeting those challenges is a design with a so-called spoke arrangement of the magnet poles. Although, a spoke type rotor topology is widely known, the influences of the rotor mechanical design on the electromagnetic performance has, largely, been overlooked, while a comparison of different feasible design solutions has not been provided to date. In this paper, a novel spoke type traction motor using ferrite magnets and based on a single piece rotor topology has been presented. The design is based on a coupled structuralelectromagnetic optimization, where the key design features, influencing the structural stress and the electromagnetic torque density have been explained. This design is, further, compared against a previously disclosed fir tree spoke type rotor solution, which has been designed for the same set of geometrical and output requirements. Through the comparisons, and for the first time, it is shown that the two alternative spoke type designs, show significant differences in performance, including torque density, efficiency, and demagnetization.
This paper presents a review of recent Air Force research efforts to develop new and improved solar absorber coatings for solar power generation. The work of several laboratories is described as it relates to a particular experimental approach or technique for producing selectively absorbing surfaces. Such unique techniques as microporous surfaces and metallo-organic solution decomposition are discussed as well as the more conventional optical interference methods. A discussion of the applications of these coatings to fulfill Air Force coatings needs in this area is also given.
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