Author: Zhi Cao
Cao, Zhi, 2025 Design, Prototyping and Analysis of Axial-Flux Induction Motor for Line-Start Applications, Flinders University, College of Science and Engineering
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Radial-flux induction motors (RFIMs) remain the predominant choice in industrial applications, largely owing to their robustness and structural simplicity. Nevertheless, their limited power density has driven increasing interest in axial-flux induction motors (AFIMs), which offer superior torque density and a more compact configuration. Despite these advantages, AFIMs remain underutilised in line-start applications due to practical challenges, such as higher manufacturing complexity, structural sensitivity, and the lack of standardised design and fabrication guidelines.
This thesis establishes a design and evaluation framework for line-start AFIMs. A geometry-driven electromagnetic design method is proposed, incorporating key constraints such as magnetic loading and current density at different radii, making the approach more aligned with the inherent characteristics of AFIMs. Additionally, material cost considerations are integrated to ensure design feasibility from both technical and economic perspectives. Multi-objective visualisation techniques are employed to reveal trade-offs and guide optimal design choices. The method is then applied to transform commercial RFIMs into AFIM counterparts for different pole numbers. A comprehensive sensitivity analysis is conducted to evaluate how variations in key geometric parameters, such as slot shape and slot number, affect the electromagnetic performance of both AFIMs and RFIMs, and to identify which parameters play a more critical role in each topology.
The work further investigates axial force, an issue that has attracted considerable attention in AFIMs. To address this, a static measurement technique is developed and validated both simulation and experimental results. This method enables accurate quantification of axial force without fully assembled thereby enabling accurate evaluation during early-stage prototyping. The outcomes provide valuable design reference for mechanical support structure, airgap management, and bearing selection in AFIM development. Various double-sided AFIM topologies are also analysed and compared to evaluate their impact on axial force mitigation and structural feasibility.
A stationary no-load testing methodology specifically developed for AFIM is proposed as an alternative to the conventional rotating no-load test. This approach enables an early-stage evaluation of motor performance without the need for rotor rotation or fully mechanical assembly. Moreover, the study introduces a classification of mechanical losses into voltage and airgap length dependent components. By employing combined strategy of stationary and rotating no-load measurements, these components can be separated, thereby providing a more accurate assessment of electromagnetic characteristics of AFIMs at the preliminary evaluation stage.
Together, these contributions form a comprehensive investigation for the efficient design, prototyping, and evaluation of line-start AFIMs, supporting their practical deployment in industrial applications.
Keywords: Radial-flux induction motor (RFIM); Axial-flux induction motor (AFIM); Line-start; Electromagnetic design; Axial force; Stationary no-load test; Sensitivity analysis; Material cost; Industrial application.
Subject: Engineering thesis
Thesis type: Doctor of Philosophy
Completed: 2025
School: College of Science and Engineering
Supervisor: Dr. Amin Mahmoudi