Thermal Performance Analysis of Line-Start Permanent Magnet Motors : A Comparative CFD Study of Conduction, Self-Ventilated, and Forced Convection Cooling in a 2.2 kW LSPM Motor = 라인스타트 영구자석 모터의 열 성능 분석: 2.2kW 라인스타트 영구자석 모터에서 전도, 자환기 및 강제 대류 냉각 방식의 비교 CFD 연구

다국어 초록 (Multilingual Abstract)

Thermal Performance Analysis of Line-Start Permanent Magnet Motors: A Comparative CFD Study of Conduction, Self-Ventilated, and Forced Convection Cooling in a 2.2 kW LSPM Motor Thermal regulation is an important design requirement for electrical machines because excessive heat accumulation can reduce efficiency, shorten insulation life, and weaken long-term operating reliability. This issue is particularly important in line-start permanent magnet (LSPM) motors, where high temperature may cause permanent magnet demagnetization and loss of electromagnetic performance. In this thesis, the thermal behavior of a 2.2 kW LSPM motor is investigated under three cooling configurations: conduction-only heat transfer, rotor-induced self-ventilated cooling, and externally supplied forced convection. A three-dimensional computational fluid dynamics model based on conjugate heat transfer was established in ANSYS Fluent to resolve heat conduction inside the solid motor components together with convective transport in the surrounding air region. The SST k–ω turbulence model was used to represent near-wall transport behavior, while the influence Sharnaliy Akter Rubina Supervised by Prof. Daeho Lee Dept. of Mechanical Engineering Graduate School of Gachon University of the rotating cooling fan was modeled using the multiple reference frame approach. Gravity was also included so that buoyancy effects could be considered in the self-ventilated case. Different boundary conditions were assigned to each cooling configuration to represent the corresponding operating environment. The numerical results show that conduction-only cooling is not sufficient for safe continuous operation, as heat remains trapped inside the motor and the peak winding temperature reaches approximately 148.2 °C. When rotor-driven self-ventilation is introduced, internal airflow improves heat removal from the housing and reduces the winding temperature to about 59.1 °C. The forced convection case provides the strongest cooling effect, further decreasing the winding temperature to approximately 45.5 °C and producing a more uniform thermal field across the motor components. The airflow velocity analysis also indicates that the cooling improvement becomes progressively smaller at higher inlet velocities, suggesting the presence of a practical saturation region. Overall, this study clarifies how conduction, self-ventilation, and forced convection influence temperature distribution, hotspot formation, and heat dissipation in a low-power industrial LSPM motor. The validated CFD-based framework provides a useful basis for evaluating cooling performance and supporting the thermal design of LSPM motors operating within safe material temperature limits.

목차 (Table of Contents)

• Chapter 1: Introduction 1
• 1.1. Background of The Study 1
• 1.2 Research Motivation and Problem Statement 5
• 1.3 Research Objectives 9
• 1.4 Significance of the Research 11
• 1.5 Thesis Structure 16
• Chapter 2: Literature Review 19
• 2.1 Thermal Analysis of Electrical Machines 19
• 2.2 Line-Start Permanent Magnet (LSPM) Motors 21
• 2.3 Thermal Modelling Approaches 23
• 2.4 Cooling Mechanisms 27
• 2.5 Research Gap 30
• Chapter 3: Motor Description and Experimental Setup 34
• 3.1 Motor Geometry & Configuration 34
• 3.2 Material Properties 39
• 3.3 Experimental Set-Up 43
• 3.4 Electromagnetic Analysis 46
• 3.5 Loss Modeling and Heat Source Distribution 48
• Chapter 4: Numerical Methodology 51
• 4.1 Governing Equation 51
• 4.2 Boundary Conditions 53
• 4.3 Turbulence Modelling 57
• 4.4 Mesh Generation and Grid Independence Study 59
• Chapter 5: Dimensionless Analysis 63
• 5.1 Dimensionless Framework 63
• 5.2 Axial Thermal-Fluid Behavior 68
• Chapter 6: Result & Discussion 76
• 6.1 Model Validation 76
• 6.2 Thermal Field Evaluation and Hotspot Behavior 79
• 6.3 Influence of Flow Regime on Convective Transport 83
• 6.4 Vorticity Field and Near-Wall Transport 87
• 6.5 Effect of External Airflow Velocity 92
• 6.6 Heat Flow Path Analysis 95
• 6.7 Quantitative Thermal Performance 98
• 6.8 Thermal Resistance Interpretation 101
• 6.9 Engineering Implications 103
• Chapter 7: Conclusion 106
• 7.1 Summary 106
• 7.2 Contribution. 108
• Chapter 8: Future Research Directions 113
• References 117