When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
With the global trend towards electrification of transport, the interest in various configurations of electric motors is growing. Surface permanent magnet synchronous machines (SPMSM) are used for many high-performance applications due to low inertia, high torque density, and overloading capability. Several applications require low torque pulsations as they can lead to mechanical vibrations and acoustic noise in the electric motor. Various techniques have been proposed in the literature to reduce the torque pulsations either by using the machine control strategies or by the machine design. Optimization of the rotor permanent magnet (PM) shape is one of the effective methods for reducing torque pulsations. Unfortunately, the low versatility of the motor magnet fabrication technologies limits the development of new motor geometries. Current techniques used for the assembly of PMs in motors such as adhesives, slots, or screws are complex, labor-intensive, and offer very little flexibility for advanced motor design geometries. Consequently, alternative fabrication techniques such as cold spray additive manufacturing are worth exploring. Cold spray additive manufacturing is used for shaping PMs for the direct fabrication of electric motor parts without the need for additional assembly steps. This novel technique allows an increase in the design flexibility of electrical machine geometries targeting improved performance.
In this thesis, the PM rotors considered are conventional rectangular-shaped with unskewed magnets (Model A), with skewed magnets (Model B), and sinusoidal-petal-shaped magnets (Model C) along the axial direction. The magnitude of magnetization current pulse required to magnetize these rotors is calculated using an FEA package and an impulse magnetizer setup is designed and prototyped for in-situ magnetization. Various stator terminal connection configurations are analyzed and compared for the magnetizer. The performance of the shaped cold sprayed permanent magnet rotors and their effects on back EMF, electromagnetic torque, and cogging torque are analyzed experimentally and comparisons are made between the different rotor designs.
Laminated electrical silicon steel sheets are mainly used to produce the stator and rotor core of an electrical machine. In comparison, there are soft magnetic composites (SMC) which consist of a high purity fine iron powder particle coated with the insulation material. Hence, its electrical resistance is much higher than that of laminated steel. Its isotropic magnetic and physical properties help flux to conduct in a three-dimensional direction and effectively dissipate the heat produced from core losses. The product developed using SMC material uses compaction, heating, and pressing techniques to achieve the desired shape and final size of the machine core parts. Hence, the material wastage is lower as compared to the laminated steel core.
In this thesis, the impact of a few manufacturing parameters on SMC properties to ensure that optimized motor performance is achieved was analyzed using three SMC different materials (A, B, and C) using FEA software. Furthermore, machine design parameters are tuned to achieve optimal flux weakening. Finally, an FEA-based performance analysis of a 7.12 kW radial flux PMSM with laminated steel and SMC stator core is used to estimate the torque density and losses in the machines. Two different designs of 24/20 slot-pole and 12/8 slot-pole configuration using conventional surface permanent magnet rotor designs are considered. In addition, the ring-type Halbach-array PM rotor fabricated using cold spray additive manufacturing for 12/8 slot-pole is analyzed and optimized with the SMC stator core for high-speed electric vehicle application.