A Ferrite PM In-Wheel Motor Without Rare Earth Materials for Electric City Commuters

Abstract

Abstract-Electric city commuters are vehicles used for commuting from suburbs to inner cities and for movement within cities. Because of the short distances that they cover and their small battery size, such vehicles are beginning to attract attention. Generally, a high-performance permanent magnet (PM) composed of rare earth elements, such as neodymium and dysprosium, is used in the inwheel PM synchronous motor (PMSM) of an electric city commuter. However, rising prices of rare earth elements and export restrictions on them are serious problems. Development of an in-wheel PMSM that does not utilize rare earth PMs is therefore highly desirable for electric city commuter vehicles. Accordingly, our research group has focused on a surface PM type axial gap structure that can achieve a high torque density and a short motor length in the axial direction. The designed motor structure with ferrite PMs replacing the rare earth PMs and the results of a three-dimensional finite element analysis are introduced in detail in this paper. Moreover, to examine the fundamental characteristics of the designed motor, a prototype is produced and tested.Index Terms-permanent magnet synchronous motor, electric city commuter, axial gap motor, surface permanent magnet rotor structure, ferrite permanent magnet

Performance Variation of Ferrite Magnet PMBLDC Motor With Temperature

“…This sets stage for renewed interest in the research of ferrite magnet machines [2]- [6] as ferrites are commonly available. The main challenges in substituting the RE magnet with the ferrite are its low remanence (B r ) and coercivity (H c ).…”

“…Though the design of ferrite magnet machines is discussed extensively in literature [2]- [6], [8], [13], [14]; the performance variation of ferrite magnet PM brushless DC (PMBLDC) motors with temperature has not been examined in detail. Also, there is a lack of systematic approach presented for identifying the leeway for armature reaction with respect to irreversible demagnetization.…”

“…In [16], the authors used the flux density distribution in magnets to estimate the level of demagnetization in a PM synchronous generator and also calculated the performance variation with temperature. In [6], the authors used BH curve of ferrite magnet corresponding to the lowest operating temperature to ensure that the field weakening operation is not causing any irreversible demagnetization in a PM synchronous motor. However, authors did not evaluate the performance variation with temperature.…”

Size and Weight Reduction of an In-Wheel Axial-Gap Motor Using Ferrite Permanent Magnets for Electric Commuter Cars

“…Consequently, our research team has proposed an axialgap-type in-wheel motor for electric commuter cars that uses ferrite PMs [7]- [9]. In general, torque is decreased by changing from rare-earth PMs to ferrite PMs because the residual magnetic flux density of the latter is only about 30% that of the former.…”

“…In previous papers, we reported on the operational characteristics of the proposed motor with results of experiments on 5-kW and 10-kW prototypes [7]- [9]. In the examinations, an open slot structure is adopted for the stator in order to reduce production costs.…”