Novel axial field switched reluctance EV motor

Dr Peter Harrop
Novel axial field switched reluctance EV motor
Nikunj R Patel and Varsha A Shah of the Department of Electrical Engineering, SV National Institute of Technology, Surat, and Makarand M Lokhande of the Department of Electrical Engineering, Visvesvaraya National Institute of Technology, Nagpur in India presented an interesting paper, "A Mathematical and FEM Design of Novel Axial Field Switched Reluctance Motor for Electrical Vehicle (EV) Application" at EVS29 in Montreal Canada recently. They noted that switched reluctance (SR) motors attract attention because they do not use permanent magnet material so they are a strong candidate for EV applications.
A novel axial field switched reluctance motor (AFSRM) design is presented which intend to improve the output torque by single flux path distribution in C- core stator while exploiting the high power density of the switched reluctance technology. Indeed, permanent magnet (PM) motors which offers high torque density and efficiency have the disadvantage of thermal problem which arises due to eddy currents. Employment of rare-earth magnetic materials which are expensive due to the monopoly of certain countries in their availability is another economical drawback. This has drawn considerable interest in research on switched reluctance motor (SRM) because it does not use any permanent magnets.
"SRM becomes a suitable candidate in Electrical Vehicle (EV) and Hybrid Electrical Vehicle (HEV) propulsion which needs high torque and high speed (1-2). SRM has advantages like simple and rugged construction high speed operation and high-fidelity against impact and vibration under off-load condition. The main problems with the SRMs are noise and high torque ripple. However, these problems are being solved by development of the power electronics devices and their controls. It is difficult to output high torque because of the absence of permanent magnet. Hence it is difficult to avoid a high current density and the motor mass becomes large due to increase in the torque. Based on field distribution SRM can be classified in to two, Radial field SRM and Axial Field SRM. Various radial field constructions of SRM are available in literature. The axial magnetic field disk type SR motors is different from the traditional radial magnetic field SR machines, whose rotor core is laminated into disk shape. Because of the special structure, the axial length of this kind of motor can be reduced compared to the radial field motor. Due to small magnetic length, axial field motor offers high torque. Various topologies of axial flux SRM (AFSRM) have been reported in the literature. In this paper a novel C-core axial field 8/6 SRM motor is proposed".
"Unlike conventional radial field SRMs, the windings of the C-core stator can be individually wound without complex winding equipment. This topology has an 8/6 pole dual air gap single rotor and single C-core stator configuration without overlapping winding arrangement. Computer Aided Design (CAD) is used to calculate the phase inductance and average torque for a novel AFSRM topology. The two and three-dimensional Finite element (FE) analyses is carried out to validate obtained CAD results".
The conclusion to their paper declares, In this paper a novel axial flux C-core switched reluctance motor is proposed for electrical vehicle application. In this topology shorter and single flux path offers good torque. It reduces leakage flux and end winding volume. This design offers easy and less skilled winding structure. The relation that exist between the physical dimensions and reluctances as well as torque where exploited for quickly arriving at the desired motor design. A 2D and 3D model are developed for performance evaluation of machine. A mathematical design is prepared for the sizing of this machine and validating the same with FEA tool".
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