Advances and Trends in PM-Free or Rare-Earth-Free PM Motors

A special issue of Machines (ISSN 2075-1702). This special issue belongs to the section "Electrical Machines and Drives".

Deadline for manuscript submissions: closed (31 January 2024) | Viewed by 11207

Special Issue Editors


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Guest Editor
School of Electrical and Electronic Engineering, Huazhong University of Science & Technology, Wuhan, China
Interests: synchronous reluctance machines; PM machines; traction motors; magnetic gears; multiphysics analysis; design and optimization

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Guest Editor
Power Electronics, Machines and Control (PEMC) Group, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK
Interests: design; analysis; intelligent control of permanent magnet and reluctance type electric machines

Special Issue Information

Dear Colleagues,

With the global drive of pursuing “Net Zero”, electrification has been making remarkable waves in the automotive industry. Many countries have set timelines to terminate the sales of conventional vehicles within the next decade. These ambitious commitments translate to significantly improved performance requirements on powertrains in pure/hybrid electric vehicles, at the very heart of which there is the electrical traction motor. Permanent magnet (PM) motors based on heavy rare earth PM materials have been widely recognized as state-of-the-art traction motor solutions due to their high efficiency and power density. A trend of traction motor development towards higher speed, higher power density, higher voltage and lower cost increase the need to incorporate and develop new machine technologies. Furthermore, the global supply chains of PM motors are facing ever-increasing challenges due to price volatility and limited availability of heavy rare-earth magnet materials. Therefore, the development of PM-free or rare-earth-free PM electric motors for EV applications is becoming more and more appealing.

PM-free motors, such as induction motors (IMs) and switched reluctance motors (SRMs), are being extensively investigated in the literature. Other potential alternatives include synchronous reluctance motors (SynRMs) and wound rotor (WR) synchronous motors, possibly assisted by permanent magnets (PMs) with lower grades. In order to meet the requirements of high power density for these non/less rare-earth PM motors, the design challenges might be significantly increased complexity of machine topology and multi-dimensional interdisciplinary constraints, such as electromagnetic, mechanical, thermal insulation, and control strategy. Therefore, the Special Issue aims to collect original research and review articles on different design and control methodologies or solutions for PM-free or rare-earth-free PM motors targeting for EV applications. The topics of interest include but are not limited to the following:

  1. Novel PM-free or rare-earth-free PM machine topologies;
  2. Anti-demagnetization techniques for traction motors with lower grade magnets;
  3. Design and optimization methods for traction motors;
  4. Multi-physical analysis of motors with complex structures;
  5. New design techniques for traction motors;
  6. Control techniques to achieve high flux-weakening capability or overload capability;
  7. NVH optimization and torque ripple suppression methods.

Prof. Dr. Yawei Wang
Dr. Tianjie Zou
Guest Editors

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Published Papers (3 papers)

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Research

12 pages, 7352 KiB  
Communication
Study on Performance Improvement through Reducing Axial Force of Ferrite Double-Layer Spoke-Type Permanent Magnet Synchronous Motor with Core Skew
by Dong-Woo Nam, Kangbeen Lee, Si-Woo Song, Won-Ho Kim and Jae-Jun Lee
Machines 2024, 12(4), 280; https://doi.org/10.3390/machines12040280 - 22 Apr 2024
Viewed by 1360
Abstract
Recently, due to the price fluctuation and supply instability of rare earth mineral resources, there has been a lot of development of electric motors using non-rare-earth permanent magnets. As a result, motors using Dy-free permanent magnets and ferrite permanent magnets are being researched, [...] Read more.
Recently, due to the price fluctuation and supply instability of rare earth mineral resources, there has been a lot of development of electric motors using non-rare-earth permanent magnets. As a result, motors using Dy-free permanent magnets and ferrite permanent magnets are being researched, and, in particular, ferrite permanent magnets often utilize spoke-type structures, which are magnetic flux concentrators, to compensate for their low coercivity and residual flux density. However, in general, spoke-type PMSMs do not use much reluctance torque, so double-layer spoke-type PMSMs have been studied for their more efficient design. Unlike general spoke-type PMSMs, double-layer spoke-type PMSMs can utilize high reluctance torque by increasing the difference between d-axis and q-axis reluctance. However, as the difference in magnetic resistance increases, vibration and noise are generated, which adversely affects the mechanical part and shortens the life of the motor. Although this problem seemed to be solved by applying core skew in the previous study, it was confirmed that the axial force caused by the axial leakage flux occurred in the maximum torque per ampere (MTPA) control section and the torque ripple was increased. Therefore, in this paper, a model that can apply symmetrical core skew and reduce axial force is proposed. First, the causes of the axial force generated in previous studies were analyzed. Based on the analysis of these causes, a new symmetrical core skew structure was proposed, and its justification was verified through FEA. Full article
(This article belongs to the Special Issue Advances and Trends in PM-Free or Rare-Earth-Free PM Motors)
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21 pages, 8071 KiB  
Article
A Study on Magnetization Yoke Design for Post-Assembly Magnetization Performance Improvement of a Spoke-Type Permanent Magnet Synchronous Motor
by Min-Jae Jeong, Kang-Been Lee, Si-Woo Song, Seung-Heon Lee and Won-Ho Kim
Machines 2023, 11(9), 850; https://doi.org/10.3390/machines11090850 - 22 Aug 2023
Cited by 1 | Viewed by 2535
Abstract
Permanent magnet synchronous motors (PMSMs) are highly affected by magnetization, which determines the magnetization level in the permanent magnet (PM). There are three main magnetization methods: single-unit, stator coil, and post-assembly magnetization. Post-assembly magnetization is widely used in PMSM mass production due to [...] Read more.
Permanent magnet synchronous motors (PMSMs) are highly affected by magnetization, which determines the magnetization level in the permanent magnet (PM). There are three main magnetization methods: single-unit, stator coil, and post-assembly magnetization. Post-assembly magnetization is widely used in PMSM mass production due to its ability to achieve high magnetization performance using a separate magnetizing yoke. However, spoke-type PMSMs with ferrite PMs face challenges when using the post-assembly method. The structural configuration of two magnets located radially hampers effective magnetized field transmission to the rotor’s interior due to the narrow space between the magnets. Maximizing the magnetization rate becomes crucial, but the limited space in the spoke-type structure complicates this. This paper addresses the issue and analyzes factors influencing post-assembly magnetization characteristics. A novel yoke structure is proposed, reducing the distance between the coil and magnet, leading to more efficient magnetization. The parametric and performance comparative analysis shows an impressive 17.1%p increase in magnetization rate with the proposed yoke structure compared to the existing yoke. This outcome contributed to a solution for enhancing the magnetization performance of spoke-type ferrite PMSMs. Full article
(This article belongs to the Special Issue Advances and Trends in PM-Free or Rare-Earth-Free PM Motors)
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20 pages, 11845 KiB  
Article
Multi-Physics Comparison of Surface-Mounted and Interior Permanent Magnet Synchronous Motor for High-Speed Applications
by Guanghui Du, Niumei Li, Qixun Zhou, Wentao Gao, Lu Wang and Tao Pu
Machines 2022, 10(8), 700; https://doi.org/10.3390/machines10080700 - 17 Aug 2022
Cited by 9 | Viewed by 6051
Abstract
For high-speed permanent magnet machines (HSPMMs), two different rotor structures are widely used: surface-mounted permanent magnet (SPM) and interior permanent magnet (IPM). The two different rotor structures have a large impact on the comprehensive performance in multiple physical fields of HSPMMs, including mechanical [...] Read more.
For high-speed permanent magnet machines (HSPMMs), two different rotor structures are widely used: surface-mounted permanent magnet (SPM) and interior permanent magnet (IPM). The two different rotor structures have a large impact on the comprehensive performance in multiple physical fields of HSPMMs, including mechanical stress, electromagnetic characteristics, and temperature distribution. However, the multi-physics comparison of two different rotor structures is rare in the existing literature, which makes it difficult for designers to choose a suitable rotor structure. Therefore, in this paper, the comprehensive performance of multi-physics for SPM and IPM is comprehensively compared and analyzed. Firstly, the SPM and IPM were designed under 60 kW and 30,000 rpm with the condition of the same stator structure, winding type and volume. Secondly, to ensure that the two rotor structures meet the stress-field constraints, a finite element model (FEM) was built in Ansys Workbench. The influence of different parameters on the rotor stress was analyzed. Following this, the electromagnetic characteristics and temperature distributions of the two motors were compared and analyzed comprehensively through the FEM. Finally, a prototype of an SPM rotor structure is selected and manufactured. The validity of the multi-physics analysis and design was verified through experimental measurements. The above analysis will provide a reference when a designer chooses a rotor structure for an HSPMM. Full article
(This article belongs to the Special Issue Advances and Trends in PM-Free or Rare-Earth-Free PM Motors)
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