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Machines
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Wound Field and Less Rare-Earth Electrical Machines in Renewables
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Wound Field and Less Rare-Earth Electrical Machines in Renewables

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

Deadline for manuscript submissions: 28 February 2026 | Viewed by 2514

Special Issue Editors

Dr. Udochukwu B. Akuru

E-Mail Website
Guest Editor
Department of Electrical Engineering, Tshwane University of Technology, Pretoria 0183, South Africa
Interests: electrical machines; power engineering; renewable energy
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Zhongze Wu

E-Mail Website
Guest Editor
School of Electrical Engineering, Southeast University, Nanjing 210096, China
Interests: wound field machines; flat-wire machines
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Efforts to transition from conventional energy resources to renewable energy are at an all-time high, being driven by global efforts towards decarbonization and clean energy as summarized in SDGs 13 and 7, respectively. Electrical machines are at the forefront of this technological revolution regarding the roles they play as key components in power generation, transportation, grid stability, aerospace and industrial automation, among others. The critical design consideration for electrical machine designers and producers is to improve performance while reducing cost. Moreover, high-energy permanent magnet (PM) machines, which are known for their premium performance, are constrained by the limited geographic resource market and adverse mining environmental impacts of rare-earth PM metals, resulting in increased material costs. On the other hand, wound field or less rare-earth PM machines have emerged as low-cost alternatives, but with performance tradeoffs.

The Special Issue aims to explore the broad value chain of wound field or less rare-earth electrical machines as enabling technologies for renewable energy transition or integration in areas such as wind power generation, road and rail transport, off-road traction, aerospace, wave energy, ship propulsion, grid stability, gravity energy storage, hydrogeneration, tidal, wave, geothermal, biomass and biogas, pumped hydro, flywheel, industrial automation and synchronous condenser, among others. The scope of the Special Issue will cover areas on multi-physics analysis, the design of novel topologies, control, evaluation, optimization, life cycle cost (LCC) and levelized cost of energy (LCOE) assessments, as well as the prototyping and experimental validation of applying the proposed electrical machines in the renewable energy landscape.

Dr. Udochukwu B. Akuru
Prof. Dr. Zhongze Wu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Machines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • machine topology
  • design and analysis
  • modeling
  • optimization
  • multi-physics
  • control
  • electrical-excited
  • wound field
  • wound rotor
  • brushless
  • field-excited
  • hybrid-excited
  • less rare earth
  • rare earth-free
  • fault tolerance
  • electric vehicle
  • wind power generation
  • multiphase
  • synchronous condenser
  • hygrogenerators
  • DC-excited
  • renewable energy

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Published Papers (2 papers)

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Research

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17 pages, 7687 KB  
Article
Locked Rotor Fault Analysis in Dual Rotor Wound Field Flux Switching Generator for Counter-Rotating Wind Turbine Application
by Wasiq Ullah, Faisal Khan, Udochukwu B. Akuru and Mehroz Fatima
Machines 2025, 13(6), 462; https://doi.org/10.3390/machines13060462 - 27 May 2025
Viewed by 1321
Abstract
In this paper, the performance of the Independent Dual Rotor Wound Field Flux Switching Generator (IDRWFFSG) under locked rotor fault scenarios and counter-rotating operational direction for fault withstand capability is investigated. The IDRWFFSG and the locked rotor fault scenarios are defined, and the [...] Read more.
In this paper, the performance of the Independent Dual Rotor Wound Field Flux Switching Generator (IDRWFFSG) under locked rotor fault scenarios and counter-rotating operational direction for fault withstand capability is investigated. The IDRWFFSG and the locked rotor fault scenarios are defined, and the magnetic path formation is explained. An integrated mathematical and electromagnetic modelling of the generator characteristics performance comprising torque quality, output power, efficiency and power factor are undertaken, based on the finite element method (FEM) under fault conditions. The electromagnetic characteristics are investigated independently for the inner and outer rotors under locked conditions while the counterpart rotor is rotated in both clockwise (CW) and counterclockwise (CCW) directions. The analysis confirms that CCW offers a comparatively better response than CW, with excellent locked rotor fault withstand capability. In the case of CCW operation, the average torque, output power, efficiency, and power factor are improved. Based on the results, it is determined that the rotational direction of the rotor is selected depending on the prerequisite demand of high efficiency, high power factor, and high output power when one of the rotors goes under a locked condition. Finally, a test prototype is developed to validate the predicted electromagnetic characteristics, of which the measured results confirm the effectiveness of the IDRWFFSG fault withstand capability study. Full article
(This article belongs to the Special Issue Wound Field and Less Rare-Earth Electrical Machines in Renewables)
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Review

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41 pages, 5164 KB  
Review
Electric Vehicle Motors Free of Rare-Earth Elements—An Overview
by Shriram Srinivasarangan Rangarajan, Chandan Kumar Shiva, Edward Randolph Collins and Tomonobu Senjyu
Machines 2025, 13(8), 702; https://doi.org/10.3390/machines13080702 - 8 Aug 2025
Viewed by 662
Abstract
Electric vehicles offer a promising alternative to traditional internal combustion engine vehicles, mitigating air and noise pollution while reducing reliance on petroleum resources. However, the widespread adoption of electric vehicles faces several challenges, including high upfront costs, limited driving range, and the availability [...] Read more.
Electric vehicles offer a promising alternative to traditional internal combustion engine vehicles, mitigating air and noise pollution while reducing reliance on petroleum resources. However, the widespread adoption of electric vehicles faces several challenges, including high upfront costs, limited driving range, and the availability of charging infrastructure. The shift toward electric vehicle motors that do not rely on rare-earth elements is an important and massive engineering undertaking. Permanent magnet synchronous motors, which use copper windings instead of permanent magnets to generate the excitation field, offer an alternative approach to reducing rare-earth material usage, with research focusing on optimizing their design and control for electric vehicle applications. Induction motors are being reconsidered for the majority of electric vehicle models due to their robust design, established manufacturing infrastructure, and absence of rare-earth magnets, offering a viable alternative with ongoing research focused on improving their efficiency and power density. New electric vehicle (EV) motors using rotors outfitted with electromagnets (i.e., wire coils) are perhaps the most promising near-term solution for producing powerful motors without REEs altogether. This paper presents an overview of electric vehicles with the possible inclusion of rare-earth-free elements. Full article
(This article belongs to the Special Issue Wound Field and Less Rare-Earth Electrical Machines in Renewables)
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