VP4-06 Air-gap Region Topology Optimization of a Hair-pin PM Motor for Electromagnetic Vibration Reduction
Creators: Peng Zhao
Xiaoyong Zhu
Jiqi Wu
Zixuan Xiang
Yutang Xiao
and Wenye Wu
Publisher: name: IEEE
Year: 2025

In recent years, Hair-pin Permanent Magnet (PM) motors, which utilize hair-pin windings in the stator and embedded permanent magnets in the rotor, have become a popular choice among electric vehicle manufacturers due to their high torque density and efficiency [1]. However, the dual-layer permanent magnet structure of these motors increases the complexity of the magnetic circuit and results in inadequate rotor rigidity at high speeds, leading to prominent vibration and noise issues [2]. This paper proposes a new method for the refined design of the regions on both sides of the air gap, aimed at improving the electromagnetic vibration characteristics of PM Hair-pin motors and enhancing motor quality. The method adaptively reshapes the air gap areas without altering the basic structure of the stator and rotor, thus reducing radial electromagnetic forces and torque fluctuations without sacrificing torque and efficiency. A 48-slot/8-pole Hair-pin PM motor with an 8-layer winding was selected as an example. Under the NGnet topology optimization algorithm, the stator tooth boot area and the rotor edge area, located on both sides of the air gap, were effectively reshaped. Fig. 1 illustrates the structure of the motor. Due to the Hair-pin windings being inserted from the end of the core, the stator slot openings are relatively small. The rotor features a double-layer V-shaped design, with strategically placed rectangular magnetic barriers between the second-layer V-shaped permanent magnets. This enhances the motor's overload capacity and improves its speed extension capability. Fig. 2(a) displays the air gap design area, which includes the stator tooth boot, the initial uniform air gap, and the rotor edge side. Fig. 2(b) shows multiple Gaussian functions uniformly arranged in the design area, with the grid materials within the area dependent on the weights of the Gaussian basis functions. Fig. 2(c) presents the optimization results of the design area. Fig. 3 illustrates the visualization process of the topological evolution of the air gap design area. Fig. 4 demonstrates that the optimization significantly reduces torque ripple and vibration acceleration. More details will be presented in the full text.References: [1] G. Bramerdorfer, J. Tapia, J. Pyrhonen and A. Cavagnino, "Modern Electrical Machine Design Optimization: Techniques, Trends, and Best Practices, " IEEE Trans. Ind. Electron, vol. 65, no. 10, pp. 7672-7684, Oct. 2018. [2] C. Peng, D. Wang, B. Wang, J. Li, C. Wang and X. Wang, "Different rotor segmented approaches for electromagnetic vibration and acoustic noise mitigation in permanent magnet drive motor: A comparative study," IEEE Trans. Ind. Electron, vol. 71, no. 2, pp. 1223-1233, Feb. 2024.
In recent years, Hair-pin Permanent Magnet (PM) motors, which utilize hair-pin windings in the stator and embedded permanent magnets in the rotor, have become a popular choice among electric vehicle manufacturers due to their high torque density and efficiency [1]. However, the dual-layer permanent magnet structure of these motors increases the complexity of the magnetic circuit and results in inadequate rotor rigidity at high speeds, leading to prominent vibration and noise issues [2]. This paper proposes a new method for the refined design of the regions on both sides of the air gap, aimed at improving the electromagnetic vibration characteristics of PM Hair-pin motors and enhancing motor quality. The method adaptively reshapes the air gap areas without altering the basic structure of the stator and rotor, thus reducing radial electromagnetic forces and torque fluctuations without sacrificing torque and efficiency. A 48-slot/8-pole Hair-pin PM motor with an 8-layer winding was selected as an example. Under the NGnet topology optimization algorithm, the stator tooth boot area and the rotor edge area, located on both sides of the air gap, were effectively reshaped. Fig. 1 illustrates the structure of the motor. Due to the Hair-pin windings being inserted from the end of the core, the stator slot openings are relatively small. The rotor features a double-layer V-shaped design, with strategically placed rectangular magnetic barriers between the second-layer V-shaped permanent magnets. This enhances the motor's overload capacity and improves its speed extension capability. Fig. 2(a) displays the air gap design area, which includes the stator tooth boot, the initial uniform air gap, and the rotor edge side. Fig. 2(b) shows multiple Gaussian functions uniformly arranged in the design area, with the grid materials within the area dependent on the weights of the Gaussian basis functions. Fig. 2(c) presents the optimization results of the design area. Fig. 3 illustrates the visualization process of the topological evolution of the air gap design area. Fig. 4 demonstrates that the optimization significantly reduces torque ripple and vibration acceleration. More details will be presented in the full text.References: [1] G. Bramerdorfer, J. Tapia, J. Pyrhonen and A. Cavagnino, "Modern Electrical Machine Design Optimization: Techniques, Trends, and Best Practices, " IEEE Trans. Ind. Electron, vol. 65, no. 10, pp. 7672-7684, Oct. 2018. [2] C. Peng, D. Wang, B. Wang, J. Li, C. Wang and X. Wang, "Different rotor segmented approaches for electromagnetic vibration and acoustic noise mitigation in permanent magnet drive motor: A comparative study," IEEE Trans. Ind. Electron, vol. 71, no. 2, pp. 1223-1233, Feb. 2024.