Design and analysis of novel electric machines for electric vehicle driving systems

Abstract

Electric machines play a pivotal role in the driving system of electric vehicles (EVs). Various types of conventional electric machines have been employed for EV applications. In addition to these conventional electric machines, emerging electric machines with enhanced performance characteristics have been proposed, including magnetic-geared machines, Vernier machines, and stator permanent magnet (PM) machines. Stator PM machines offer several advantages, such as improved heat dissipation efficiency, a simple and robust rotor structure, and well-established control strategies. Among stator PM machine variants, flux-switching PM (FSPM) machines have garnered significant attention due to their superior torque and power density as well as reduced torque ripple. In this study, novel stator-dual-set PM FS (SDSPM-FS) machines are proposed and analyzed with the aim of enhancing the torque and fault-tolerance capabilities of FSPM machines. In this thesis, E-core SDSPM-FS machines with diverse topologies are proposed, wherein an additional set of strategically integrated PMs is incorporated into various positions on the stator iron core, encompassing the stator tooth tips and slot openings. This arrangement establishes parallel flux circuits between the two sets of PMs, thereby improving the utilization ratio of the stator iron core and mitigating magnetic saturation on the stator yoke and teeth. Simultaneously, it enhances the effective harmonics of the stator magnetomotive force (MMF) excited by the PMs and modulated by the stator teeth, resulting in increased magnitudes of main working harmonics for air-gap flux density. Consequently, these improvements significantly enhance both output torque and power efficiency in comparison to conventional E-core FSPM machines. In order to optimize structural parameters, a global optimization approach is employed for these proposed machines, followed by a comprehensive comparison with their conventional counterparts. Furthermore, a prototype of the E-core SDSPM FS machines is manufactured to validate their performance through various experimental tests. In addition, in this thesis, consequent-pole SDSPM-FS machines with various PM arrangements are proposed. Fault-tolerance teeth and an additional set of surface-mounted PMs have been integrated into the consequent-pole FSPM machines, providing mechanical and magnetic isolation between coils belonging to different phases of the armature winding, thereby improving fault-tolerance capability. Moreover, by parallelizing the main flux circuits of the surface-mounted PMs and spoke-type PMs, phase flux linkage and no-load back electromotive force (EMF) are significantly increased in these machines. Consequently, torque capability is superior to conventional designs. A comparative study between the proposed SDSPM-FS machines and conventional consequent-pole FSPM machines is presented after the global optimization of these machines. Finally, a prototype U-type consequent-pole SDSPM-FS machine is fabricated and subjected to both no-load and on-load tests to validate the effectiveness of the proposed design. Furthermore, a comprehensive conclusion is provided to summarize this thesis, emphasizing the enhanced performance of the novel FSPM machines proposed in this study. Moreover, future research directions are indicated to offer valuable insights for further advancements of FSPM machines in EV applications.