VP4-10 High Power Density PM Motor for Electric Aircraft Propulsion Utilizing Litz Wire and Hairpin Winding Technologies
Creators: Anh Thanh Huynh
Hailin Huang
Jianan Jiang
Tianjie Zou
David Gerada
Tao Yang
and Chris Gerada*
Publisher: name: IEEE
Year: 2025

Choosing the right winding technology is crucial for enhancing power density and efficiency in aircraft propulsion systems. This paper compares 1MW-class PM motors with Litz wire and hairpin winding technologies. Models with 72 slots/12 poles are optimized using a MOGA method to maximize power density and efficiency. The impact on power density, loss distribution, efficiency, and thermal performance is thoroughly investigated. Results show significant power density improvement with hairpin winding due to shorter stack and reduced end-winding lengths, despite higher AC copper losses limiting the high-efficiency region. To mitigate copper losses and further improve efficiency, optimization through a new motor constant is applied to the design of hairpin winding and stator slots. Finally, FEA validates the machine's performance and confirms the effectiveness of the optimization. Fig. 1 (a) and (b) depict models of 1MW class PM machines with 5-stage Halbach PM utilizing Litz wires and Hairpin windings. The machines are designed with identical specifications, featuring 72 slots/12 poles and the same stator outer diameter. The study employs the Multi-Objective Genetic Algorithm (MOGA) to optimize both designs, maximizing power density and efficiency while satisfying specified constraints. Subsequently, the new motor constant combined with a Genetic Algorithm (GA) is employed to optimize the design parameters of the hairpin winding and stator slot to maximize the high-efficiency operating region. Fig. 2 shows the optimization outcomes from a MOGA for a 1MW-class PM machine with Litz wire and hairpin winding. The Litz wire machine achieves 30 kW/kg power density and 98% efficiency (Fig. 3a). In contrast, the hairpin winding machine attains 38.7 kW/kg power density with the same efficiency (Fig. 3b) due to reduced stack and end-winding lengths. Fig. 3 shows the results of optimizing hairpin winding and stator slot design using a new motor constant and Genetic Algorithm (GA). The 1MW PM motor's power density remains 38.7 kW/kg, while efficiency increases to 98.5% due to reduced copper losses from 33 kW to 27 kW. The full paper will present a detailed analysis.References: [1] European Commission, Flightpath 2050: Europe's vision for aviation; maintaining global leadership and serving society's needs; report of the High-Level Group on Aviation Research. Luxemburg: Publications Office of the European Union, 2012 [2] W. Cao et al., "Overview of electric motor technologies used for more electric aircraft (MEA)," IEEE Trans. Ind. Electron., vol. 59, no. 9, pp. 3523–3531, Sep. 2012. [3] E. Preci et al., "Rectangular and Random Conductors: AC Losses Evaluations and Manufacturing Considerations," IECON 2020 The 46th Annual Conference of the IEEE Industrial Electronics Society, Singapore, 2020, pp. 1076-1081. [4] A. Bardalai et at., "AC loss Analysis in Winding of Electrical Machines with varying Strands-in-hand and Bundle Shapes," 2020 23rd International Conference on Electrical Machines and Systems (ICEMS), Hamamatsu, Japan, 2020, pp. 845-850. [5] T.A. Huynh, V.H. Che, M.-F. Hsieh, "Maximization of High-efficiency Operating Range of Spoke-type PM E-bike Motor by Optimization through New Motor Constant," EEE Trans. Ind.Appl., vol. 59, no. 2, pp. 1328 - 1339, 2023.
Choosing the right winding technology is crucial for enhancing power density and efficiency in aircraft propulsion systems. This paper compares 1MW-class PM motors with Litz wire and hairpin winding technologies. Models with 72 slots/12 poles are optimized using a MOGA method to maximize power density and efficiency. The impact on power density, loss distribution, efficiency, and thermal performance is thoroughly investigated. Results show significant power density improvement with hairpin winding due to shorter stack and reduced end-winding lengths, despite higher AC copper losses limiting the high-efficiency region. To mitigate copper losses and further improve efficiency, optimization through a new motor constant is applied to the design of hairpin winding and stator slots. Finally, FEA validates the machine's performance and confirms the effectiveness of the optimization. Fig. 1 (a) and (b) depict models of 1MW class PM machines with 5-stage Halbach PM utilizing Litz wires and Hairpin windings. The machines are designed with identical specifications, featuring 72 slots/12 poles and the same stator outer diameter. The study employs the Multi-Objective Genetic Algorithm (MOGA) to optimize both designs, maximizing power density and efficiency while satisfying specified constraints. Subsequently, the new motor constant combined with a Genetic Algorithm (GA) is employed to optimize the design parameters of the hairpin winding and stator slot to maximize the high-efficiency operating region. Fig. 2 shows the optimization outcomes from a MOGA for a 1MW-class PM machine with Litz wire and hairpin winding. The Litz wire machine achieves 30 kW/kg power density and 98% efficiency (Fig. 3a). In contrast, the hairpin winding machine attains 38.7 kW/kg power density with the same efficiency (Fig. 3b) due to reduced stack and end-winding lengths. Fig. 3 shows the results of optimizing hairpin winding and stator slot design using a new motor constant and Genetic Algorithm (GA). The 1MW PM motor's power density remains 38.7 kW/kg, while efficiency increases to 98.5% due to reduced copper losses from 33 kW to 27 kW. The full paper will present a detailed analysis.References: [1] European Commission, Flightpath 2050: Europe's vision for aviation; maintaining global leadership and serving society's needs; report of the High-Level Group on Aviation Research. Luxemburg: Publications Office of the European Union, 2012 [2] W. Cao et al., "Overview of electric motor technologies used for more electric aircraft (MEA)," IEEE Trans. Ind. Electron., vol. 59, no. 9, pp. 3523–3531, Sep. 2012. [3] E. Preci et al., "Rectangular and Random Conductors: AC Losses Evaluations and Manufacturing Considerations," IECON 2020 The 46th Annual Conference of the IEEE Industrial Electronics Society, Singapore, 2020, pp. 1076-1081. [4] A. Bardalai et at., "AC loss Analysis in Winding of Electrical Machines with varying Strands-in-hand and Bundle Shapes," 2020 23rd International Conference on Electrical Machines and Systems (ICEMS), Hamamatsu, Japan, 2020, pp. 845-850. [5] T.A. Huynh, V.H. Che, M.-F. Hsieh, "Maximization of High-efficiency Operating Range of Spoke-type PM E-bike Motor by Optimization through New Motor Constant," EEE Trans. Ind.Appl., vol. 59, no. 2, pp. 1328 - 1339, 2023.