Presentation Information
[P1-42]A new magnetization methods that supports high-performance magnets applied to IPMSMs for EV/HEV and new motors such as spoke type motor
*Michitaka Hori1, Naoya Tomita1, Kazuki Akiyama1 (1. Nihon Denji Sokki Co., LTD. (Japan))
Keywords:
magnetization method,high performance magnets,EV/HEV,IPMSM,spoke type motor
Recently, the trend toward electrification of automobiles, aircraft, and other vehicles has accelerated due to regulations on carbon dioxide emissions. The interior permanent magnet synchronous motor (IPMSM) is used as the main electric motor. The permanent magnets used in IPMSMs require improved performance because the motors are used at extremely high speeds and high temperatures. Permanent magnets, the main material in EV/HEV main motors, often use neodymium sintered magnets, but there has been an issue with the reduction in coercivity due to high temperatures, including the effects of eddy currents. In addition, there is a risk of an unstable supply of heavy rare earth materials due to resource issues.
For these reasons, there is an acceleration in the development of neodymium sintered magnets, such as improving the coercivity by reducing the crystal grain size, and of samarium magnets. Along with magnet development, motor development is also being promoted to improve motor efficiency by even 1% as a measure against global warming. For IPMSMs, models with various magnet arrangements have been developed. One of these, the spoke-type motor, is attracting attention.
When magnetizing the magnets of IPMSM, there are two methods: a pre-magnetization method, in which a magnet is magnetized alone and then embedded in the rotor, and a post-magnetization method, in which an unmagnetized magnet is embedded in the rotor and then magnetized; however, the post-magnetization method is considered better from the perspective of efficiency in the production process.
However, in the case of the post-magnetization method, depending on the arrangement of the magnets, if the magnetizing magnetic field has an angle θ with respect to the orientation direction of the magnet, only the cosθ component of the magnetizing magnetic field is effective [1], so a larger magnetizing magnetic field is required.
Due to this industrial background, post-magnetization of magnets in IPMSMs is becoming more difficult every year, and the durability of the equipment used for magnetization is also becoming an issue. As one method to solve these problems, we have reported that magnetization of heated hot-deformed neodymium magnets can be performed sufficiently with a practical magnetizing magnetic field through basic experiments [2].
In this study, we propose a post-magnetization method in which IPMSMs rotors with high-performance permanent magnets are rapidly heated using induction heating, and report on the feasibility of introducing this method to rotor mass production lines based on experimental results. As shown in Figure 1, the magnetic field strength required for magnetization is reduced by 42% compared to the conventional method, and the magnetizing current required for magnetization is also significantly reduced by 73%, making it possible to improve magnetization and the durability of the magnetizer.In spoke-type motors, magnets are arranged radially toward the center of the rotor, making it difficult to magnetize them using conventional methods. For this reason, we propose a new magnetization method from the inside and outside as shown in Figure 2, making effective use of the magnetizing magnetic field that is simultaneously generated from the inner circumference using a flux barrier placed on the rotor.
In the industrial world, magnet and motor development is accelerating due to environmental and resource issues, and we will report on the latest trends in magnetization technology, which is an important element in the production process. We hope that this report will be of help in the research and development of permanent magnets and motors.
[1].M.Hori, “The Angular Dependence of The Magnetizing Magnetic Field of Neodymium Sintered Magnets”, IEE Japan, Annual meeting.2023,5-042
[2]. M.Hori, ”Heat magnetizing method for high-performance neodymium magnets for EV and HEV motors”, IEEE, Intermag, Permanent Magnet Machines IV, Permanent Magnet Machines I .2023
For these reasons, there is an acceleration in the development of neodymium sintered magnets, such as improving the coercivity by reducing the crystal grain size, and of samarium magnets. Along with magnet development, motor development is also being promoted to improve motor efficiency by even 1% as a measure against global warming. For IPMSMs, models with various magnet arrangements have been developed. One of these, the spoke-type motor, is attracting attention.
When magnetizing the magnets of IPMSM, there are two methods: a pre-magnetization method, in which a magnet is magnetized alone and then embedded in the rotor, and a post-magnetization method, in which an unmagnetized magnet is embedded in the rotor and then magnetized; however, the post-magnetization method is considered better from the perspective of efficiency in the production process.
However, in the case of the post-magnetization method, depending on the arrangement of the magnets, if the magnetizing magnetic field has an angle θ with respect to the orientation direction of the magnet, only the cosθ component of the magnetizing magnetic field is effective [1], so a larger magnetizing magnetic field is required.
Due to this industrial background, post-magnetization of magnets in IPMSMs is becoming more difficult every year, and the durability of the equipment used for magnetization is also becoming an issue. As one method to solve these problems, we have reported that magnetization of heated hot-deformed neodymium magnets can be performed sufficiently with a practical magnetizing magnetic field through basic experiments [2].
In this study, we propose a post-magnetization method in which IPMSMs rotors with high-performance permanent magnets are rapidly heated using induction heating, and report on the feasibility of introducing this method to rotor mass production lines based on experimental results. As shown in Figure 1, the magnetic field strength required for magnetization is reduced by 42% compared to the conventional method, and the magnetizing current required for magnetization is also significantly reduced by 73%, making it possible to improve magnetization and the durability of the magnetizer.In spoke-type motors, magnets are arranged radially toward the center of the rotor, making it difficult to magnetize them using conventional methods. For this reason, we propose a new magnetization method from the inside and outside as shown in Figure 2, making effective use of the magnetizing magnetic field that is simultaneously generated from the inner circumference using a flux barrier placed on the rotor.
In the industrial world, magnet and motor development is accelerating due to environmental and resource issues, and we will report on the latest trends in magnetization technology, which is an important element in the production process. We hope that this report will be of help in the research and development of permanent magnets and motors.
[1].M.Hori, “The Angular Dependence of The Magnetizing Magnetic Field of Neodymium Sintered Magnets”, IEE Japan, Annual meeting.2023,5-042
[2]. M.Hori, ”Heat magnetizing method for high-performance neodymium magnets for EV and HEV motors”, IEEE, Intermag, Permanent Magnet Machines IV, Permanent Magnet Machines I .2023
