The Influence of Permanent Magnet Material Properties on Generator Rotor Design

Abstract

Due to the price and supply insecurities for rare earth metal-based permanent magnet (PM) materials, a search for new PM materials is ongoing. The properties of a new PM material are not known yet, but a span of likely parameters can be studied. This paper presents an investigation on how the remanence and recoil permeability of a PM material affect its usefulness in a low speed, multi-pole, and PM synchronous generator. Demagnetisation is also considered. The investigation is carried out by constrained optimisation of three different rotor topologies for maximum torque production for different PM material parameters and a fixed PM maximum energy. The rotor topologies used are surface mounted PM rotor, spoke type PM rotor and an interior PM rotor with radially magnetised PMs. The three different rotor topologies have their best performance for different kinds of materials. The spoke type PM rotor is the best at utilising low remanence materials as long as they are sufficiently resistant to demagnetisation. The surface mounted PM rotor works best with very demagnetisation resistant PM materials with a high remanence, while the radial interior PM rotor is preferable for high remanence materials with low demagnetisation resistance.interact with the demagnetisation magnetic flux density curve. Different rotor topologies have been studied previously. In [13], three topologies, similar to those studied here, are compared for use in 4-pole traction motors for trains. Similar topologies are compared for use as an aircraft starter-generator in [14]. Five different topologies, not including the spoke-type rotor, are compared in [15]. Ref. [16] also compares five different topologies, including the spoke-type rotor. Ref.[17] compares machines with Nd-Fe-B, Sm-Co and alnico for surface mounted 4-pole machines. Ref.[18] compares three machine configurations for interior v-shaped magnets for two different materials: the novel material NdFe 12 N x and a conventional Nd-Fe-B magnet. A spoke-type rotor with ferrites is compared to a rotor with surface mounted Nd-Fe-B magnets for a wind power generator in [19,20]. A comparison of demagnetization risk for the same generator types is presented in [21].The aim of this paper is to study how the magnetic properties of PM materials affect the machine design in low-speed radial flux PM generators. To our knowledge, there has not been any previous study combining material properties with rotor design and rotor topology choice. The results from this study could give hints on which property to improve when developing new PM materials as well as on the suitability of a material with certain magnetic properties for different generator topologies.

Permanent Magnet Synchronous Machines

“…This trend can be seen in this special issue as a majority of the papers deals with PM motors with an emphasis on motor control. Five of the fifteen contributions target renewable energy sources [2][3][4]9,10], whereas the rest are focused on electric motors, with most examining electric vehicles [1,[5][6][7][8][11][12][13][14][15]. Three of the papers address brushless DC (BLDC) motors [7,11,12].…”

“…Almost all the papers in this special issue are based on NdFeB-magnets, as stated by the authors in references [10][11][12][13] or as assumed from the contents in references [1,[4][5][6][7][8][9]14,15]. However, paper [3] investigates a span of magnetic properties, which could fit any magnet material. The generators in reference [2] have electromagnets.…”

“…PM machines can have many different machine topologies. Comparison between different topologies is performed through the finite element method (FEM) simulations in reference [3] and reference [14]. In reference [14], four different machine types for six-phase outer rotor machines are compared.…”

“…The study concludes that the Vernier PM machine has best operating performance and best fault tolerance capability according to the comparison performed in this study. The study in reference [3] focuses on evaluating a novel PM material by studying a span of values for material properties and their influence on rotor design. The three rotor topologies studied are: surface mounted PM rotor, interior spoke type PM rotor and interior PM rotor with radially magnetized magnets.…”

“…This special issue contains the successful invited submissions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] to a Special Issue of Energies on the subject area of "Permanent Magnet Synchronous Machines". Interest in permanent magnet (PM) synchronous machines is continuously increasing worldwide.…”