Impact of Soft Magnetic Material on Design of High-Speed Permanent-Magnet Machines

Abstract

Abstract-This paper investigates the effect of two soft magnetic materials on a high speed machine design, namely 6.5% Silicon Steel and Cobalt-Iron alloy. The effect of design parameters on the machine performance as an aircraft starter-generator is analysed. The material properties which include B-H characteristics and the losses are obtained at different frequencies under an experiment and used to predict the machine performance accurately. In the investigation presented in this paper, it is shown that machines designed with 6.5% Silicon Steel at a high core flux density has lower weight and lower losses than the Cobalt-Iron alloy designs. This is mainly due to the extra weight contributed by the copper content especially in the end-windings. Due to the high operating frequencies, the core-losses in the Cobalt-Iron machine designs are found to outweigh the copper-losses incurred in the Silicon Steel machines. It is also shown that change in stack length/number of turns has a considerable effect on the copper losses at starting, however has no significant advantage on rated efficiency which happens to be in a field-weakening operating point. It is also shown that the performance of the machine designs depend significantly on material selection and the operating point of the core. The implications of the variation of design parameters on the machine performance is discussed and provides insight into the influence of parameters that effect overall power density.Index Terms-Aircraft, cobalt steel, flux density, high speed, machine design, soft magnetic material, silicon steel

Considerations on the Effects That Core Material Machining Has on an Electrical Machine's Performance

“…In literature, the variations in the material properties and core loss due to the manufacturing process on the stator core are investigated in [3][4][5][6][7][8][9][10][11][12][13]. However, there is a very small amount of literature that considers the effect of machining processes on the actual machine performance.…”

“…In this work, a single sheet lamination, with different amount of cuts, has been used for evaluating the magnetic properties which then is used to determine the operating behaviour of the PM machine. In [9], the authors investigate the effect of 6.5% Silicon Steel (SiFe) and CoFe alloy materials on machine performance where the application is quite high speed and therefore material properties play even a bigger role. The magnetic material properties are experimentally characterized by using a conventional single sheet tester in order to obtain the anhysteretic BH curves and the specific core loss.…”

“…Table II gives an overview of the CoFe material properties that were obtained from the manufacturer's datasheet. In order to accurately characterise these samples, a state of the art [9] testing facility that is available in-house was used to characterize these samples. Table III presents the specifications of the measuring system which is presented more in detail in [9,27].…”

“…In order to accurately characterise these samples, a state of the art [9] testing facility that is available in-house was used to characterize these samples. Table III presents the specifications of the measuring system which is presented more in detail in [9,27]. The core loss tests and BH magnetization curves at high frequency and high flux density for the slotted stator core and for the lamination sheet are performed under pure sinusoidal wave excitation.…”

“…It is well known [3][4][5][6][7][8][9][10][11][12][13] that these manufacturing processes all have a significant and permanent effect on the magnetic properties of the material, especially on the BH curve and the specific core loss properties of the material. This implies that the materials being used for the actual machine no longer reflect the material properties given by their original data sheets.…”