Author ORCID Identifier

https://orcid.org/0000-0002-0413-7026

Date Available

4-23-2025

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Engineering

Department/School/Program

Electrical and Computer Engineering

Faculty

Dr. Dan M. Ionel

Faculty

Dr. Daniel Lau

Abstract

The design and optimization of electric machines face increasing demands for efficiency, improved torque density, manufacturability, and effective utilization of materials. Meeting these demands is particularly vital in for example, electric vehicles (EVs) and renewable energy systems, where performance, reliability, and cost are critical. In this dissertation innovative field-intensifying electric machine configurations have been explored, emphasizing advanced topologies, computational modeling, and optimization techniques to advance the state of the art in electric machine design and analysis.

Electric machines with high torque density are essential for many low-speed direct-drive systems, such as wind turbines, in-wheel traction, and industrial automation. This dissertation investigates advanced analysis, optimization strategies, and design methodologies for electric machines with field-intensifying configurations. The focus is on enhancing performance metrics such as torque density, efficiency, and manufacturability while addressing challenges related to material costs and system complexity.

Following the introduction, Chapter 2 begins with a novel generator topology is then proposed for direct-drive wind turbines, integrating concentrated AC windings and field-intensifying spoke-type permanent magnets within the stator. This configuration enables the use of non-rare-earth magnets while maintaining performance metrics comparable to traditional rare-earth PM machines. Multi-objective optimization using 2D finite element analysis minimizes losses, reduces active mass, and enhances efficiency, providing a sustainable and cost-effective solution for renewable energy applications.

In Chapter 3 a new two-level optimization method is introduced to mitigate torque ripple in synchronous flux-switching and hybrid excitation machines. The innovative multi-point spline pole shaping technique significantly reduces torque ripple while improving electromagnetic torque. Validated through experimental tests and structural stress analysis, this approach ensures manufacturability and operational stability at high speeds.

Chapter 4 delves into harmonic and non-linearity of the MAGNUS machine, a dual-stator axial-flux permanent magnet vernier machine (AFPMVM) with a field-intensifying spoke-type permanent magnet rotor. Featuring a novel single-wound dual-stator design, this configuration achieves a high flux concentration ratio and a nearly unity saliency ratio. A comprehensive analysis reveals that non-linearity exists in the MAGNUS machine only because of the open circuit field from the PMs and the high harmonic content leads to non-saliency, despite the machine’s spoke-type rotor configuration. Through detailed investigation of inductance components using different methods, this non-salient behavior is thoroughly demonstrated.

Furthermore, the study shows that the machine exhibits high inductance, primarily dominated by differential leakage inductance, which presents opportunities for flux weakening operation. Also, the MAGNUS machine exhibits no non-linearity under different loading, attributed to the high equivalent airgap from the armature reaction perspective and the dominance of differential leakage inductance, which together prevent magnetic saturation up to high current densities.

The dissertation continues with an optimization study in Chapter 5, tailored for specific drive cycles, focusing on the MAGNUS machine’s application in electric vehicle (EV) in-wheel traction. A computationally efficient finite element analysis (CEFEA) method, combined with drive cycle analysis and differential evolution optimization, achieves a broad constant power range and superior torque density compared to commercially available EV traction motors. The analysis also explores flux-weakening methods to improve operational versatility. An extensive comparative study was conducted, by performing a separate optimization study and evaluating three distinct rotor configurations: a spoke-type, a Halbach array, and a surface-mounted PM rotor. Through comprehensive 3-D electromagnetic finite element analysis and differential evolution optimization, the research systematically compared these rotor designs, demonstrating the machine’s adaptability and performance potential for electric vehicle traction applications.

By advancing the design and optimization of field-intensifying electric machines, this dissertation provides solutions for different challenges in renewable energy and electric transportation, contributing to the next generation of high-performance, sustainable electric machines.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.15

Funding Information

This dissertation is based upon work supported by the National Science Foundation (NSF) under Award No. #1809876. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF.

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