arxiv: 2605.05853 · v1 · submitted 2026-05-07 · 📡 eess.SY · cs.SY

Recognition: unknown

Investigation of Wound Field Synchronous Machines using Soft Magnetic Composites for Automotive Applications

Andreas Carlsson , Christian Sandstr\"om , Viktor Josefsson , Lisa Kjell\'en , Taha El Hajji , Marcus Lenberg

Authors on Pith no claims yet

Pith reviewed 2026-05-08 07:09 UTC · model grok-4.3

classification 📡 eess.SY cs.SY

keywords soft magnetic compositeswound field synchronous machineselectrically excited synchronous machinesautomotive tractionrare-earth free motorselectric drive unitWLTP drive cyclestator materials

0 comments

The pith

Soft magnetic composites in the stator of a wound-field synchronous machine raise drive-unit efficiency to 89.7 percent over the WLTP cycle without rare-earth magnets.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tests soft magnetic composites in the stators of radial-flux wound-field synchronous machines meant for electric cars. It identifies one combination—an SMC stator paired with 0.35 mm NO35 laminated steel in the rotor—that improves both torque and efficiency over earlier designs. When the motor is placed inside a complete electric drive unit, the system reaches 89.7 percent efficiency across the WLTP drive cycle. This figure is 1.4 percentage points higher than the efficiency of a comparable permanent-magnet machine. The change removes all rare-earth content and allows thicker rotor laminations that lower material cost.

Core claim

The investigation shows that the material pairing of a soft magnetic composite stator with 0.35 mm NO35 laminated steel in the rotor produces higher torque and efficiency than conventional lamination stacks in radial-flux electrically excited synchronous machines. When this motor is integrated into a full electric drive unit, the resulting system delivers 89.7 percent efficiency over the WLTP drive cycle, an improvement of 1.4 percentage points relative to a reference permanent-magnet synchronous machine EDU. The configuration eliminates rare-earth magnets, permits thicker rotor laminations, and yields environmental advantages from SMC use.

What carries the argument

The optimal stator-rotor material pair consisting of soft magnetic composite in the stator and 0.35 mm NO35 laminated steel in the rotor, which improves torque density and reduces losses in a radial-flux electrically excited synchronous machine.

If this is right

The motor reaches 89.7 percent efficiency over the WLTP drive cycle when placed in a complete electric drive unit.
This efficiency is 1.4 percentage points higher than that of a reference permanent-magnet synchronous machine EDU.
The design removes all rare-earth materials from the machine.
Thicker laminations become usable in the rotor, lowering material expense.
SMC utilization supplies environmental benefits compared with traditional permanent-magnet machines.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Automotive suppliers could substitute this material combination for permanent-magnet motors to reduce exposure to rare-earth price volatility.
The same stator-rotor pairing might be evaluated in other radial-flux machine types beyond passenger vehicles.
A life-cycle assessment comparing the SMC-based motor to a permanent-magnet motor would quantify the claimed environmental gains.

Load-bearing premise

The finite-element models and material data inputs correctly forecast the torque, losses, and drive-cycle efficiency that a physical motor built with the chosen SMC and lamination pair would actually achieve.

What would settle it

Construct a prototype motor using the selected SMC stator and 0.35 mm NO35 rotor laminations, then measure its efficiency over the WLTP cycle on a dynamometer and compare the result to the reported 89.7 percent figure.

Figures

Figures reproduced from arXiv: 2605.05853 by Andreas Carlsson, Christian Sandstr\"om, Lisa Kjell\'en, Marcus Lenberg, Taha El Hajji, Viktor Josefsson.

**Figure 1.** Figure 1: PMSM motor 2U topology. The reference PMSM is a state-of-the-art traction motor designed for automotive applications, delivering 270 kW of peak power, as shown in view at source ↗

**Figure 2.** Figure 2: WFSM outline and topology. 7 view at source ↗

**Figure 3.** Figure 3: WLTP EDU energy consumption map over the full cycle. Color bar represents the view at source ↗

read the original abstract

This paper investigates the application of soft magnetic composites (SMCs) in the stators of wound field synchronous machines for automotive traction. While SMCs are traditionally employed in axial flux topologies, this study examines their use in radial-flux electrically excited synchronous machines (EESMs). Multiple SMC materials and lamination thicknesses are evaluated, with the optimal configuration combining a SMC material in the stator and 0.35 mm NO35 laminated steel in the rotor. This combination delivers improved torque and efficiency compared to conventional designs. When integrated into a full electric drive unit (EDU), this motor achieves 89.7% efficiency over the WLTP drive cycle, representing a 1.4 percentage point improvement over a reference permanent magnet synchronous machine-based EDU. The proposed solution eliminates rare-earth materials, reduces cost through thicker laminations, and offers environmental benefits through SMC utilization. This novel material combination, previously unexplored for radial EESMs, presents a promising direction for affordable, high-efficiency, rare-earth-free automotive traction machines.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

FEA screening picks an SMC stator with 0.35 mm NO35 rotor for a radial EESM and reports 89.7 % WLTP EDU efficiency (1.4 pp over PMSM reference), but the numbers rest on uncalibrated simulations.

read the letter

The paper's main result is a simulation study that screens several soft magnetic composite grades and rotor lamination thicknesses for a wound-field synchronous machine, settles on an SMC stator paired with 0.35 mm NO35 steel in the rotor, and then folds the resulting torque and loss maps into a full electric drive unit model. Over the WLTP cycle that combination reaches 89.7 % efficiency, 1.4 points above their permanent-magnet reference. They correctly flag that this particular radial-flux pairing has not been examined before and that it removes rare-earth magnets while allowing thicker rotor laminations for cost reasons. The material-selection approach itself is straightforward and the system-level integration gives a usable sense of drive-cycle impact. That part of the work is useful for anyone already modeling EV traction motors. The obvious weakness is the complete absence of hardware validation. Every efficiency number comes from finite-element runs whose material loss coefficients and B-H curves are taken as given; there is no mention of how those inputs were measured on the actual compacted SMC or how the models were checked against a prototype. Selecting the single best pair after evaluating multiple options also leaves open the possibility that the reported margin is partly an artifact of the simulation assumptions. The stress-test concern about offsets in SMC properties is therefore on target. This is the kind of targeted material study that motor-design groups in automotive R&D would find worth reading, even if they treat the absolute numbers as preliminary. It is solid enough on its own terms to go to peer review, provided the referees insist on either prototype data or a much fuller account of the FEA calibration and material characterization steps.

Referee Report

3 major / 2 minor

Summary. The manuscript investigates the application of soft magnetic composites (SMCs) in the stators of radial-flux wound-field synchronous machines (EESMs) for automotive traction. Multiple SMC grades and rotor lamination thicknesses are evaluated via finite-element analysis (FEA); the optimal combination (SMC stator with 0.35 mm NO35 laminated rotor) is integrated into a full electric drive unit (EDU) model and reported to deliver 89.7 % efficiency over the WLTP cycle, a 1.4 percentage-point improvement over a reference PMSM-based EDU. The work emphasizes elimination of rare-earth materials, cost reduction via thicker laminations, and environmental benefits.

Significance. If the FEA predictions prove accurate in hardware, the study offers a concrete rare-earth-free traction-machine topology with quantified drive-cycle gains. The systematic material-pair evaluation and full-EDU integration provide reusable design data for the community. The novelty of SMC use in radial-flux EESMs is a clear contribution, though the absence of experimental calibration limits immediate applicability.

major comments (3)

[Electromagnetic modeling and drive-cycle results] The headline 89.7 % WLTP efficiency and 1.4 pp gain are obtained by integrating FEA-derived torque and loss maps into an EDU model. No hardware validation or calibration of the SMC B-H curves, loss coefficients, or combined stator-rotor loss model is described, directly affecting the reliability of the central performance claim.
[Material evaluation and optimization] The optimal SMC-lamination pair is selected after evaluating multiple configurations. The manuscript should state the pre-defined selection criterion and report performance metrics for all tested pairs (or at least the next-best options) to demonstrate that the reported advantage is not an artifact of post-hoc choice.
[Comparison with PMSM reference] The reference PMSM EDU used for the 1.4 pp comparison must be specified in detail (identical power rating, voltage, cooling, and control strategy) so that the efficiency delta can be reproduced and attributed unambiguously to the SMC-rotor combination.

minor comments (2)

[Figures] Figure captions and axis labels for efficiency maps and loss breakdowns should include explicit units and scaling information for clarity.
[Material modeling] A short discussion of typical SMC density variation and cutting-edge effects on loss coefficients would help readers assess model uncertainty.

Simulated Author's Rebuttal

3 responses · 1 unresolved

We thank the referee for the constructive and detailed review of our manuscript. We have addressed each major comment below and revised the manuscript to improve transparency and completeness where feasible.

read point-by-point responses

Referee: The headline 89.7 % WLTP efficiency and 1.4 pp gain are obtained by integrating FEA-derived torque and loss maps into an EDU model. No hardware validation or calibration of the SMC B-H curves, loss coefficients, or combined stator-rotor loss model is described, directly affecting the reliability of the central performance claim.

Authors: We agree that experimental validation would further strengthen the results. This study is a simulation-based investigation relying on manufacturer-provided B-H and loss data for SMCs and laminations, together with established FEA practices. We have added a new subsection discussing the modeling assumptions, data sources, and references to literature on the accuracy of similar SMC FEA models. We believe this provides appropriate context for the comparative claims while acknowledging the simulation-only nature of the work. revision: partial
Referee: The optimal SMC-lamination pair is selected after evaluating multiple configurations. The manuscript should state the pre-defined selection criterion and report performance metrics for all tested pairs (or at least the next-best options) to demonstrate that the reported advantage is not an artifact of post-hoc choice.

Authors: The selection was guided by maximizing WLTP-cycle efficiency while preserving torque density and considering cost implications of thicker laminations. We have revised the manuscript to state this criterion explicitly in the methods section and added a table summarizing efficiency, torque, and loss metrics for all evaluated SMC grades paired with the different rotor lamination thicknesses, including the next-best configurations. revision: yes
Referee: The reference PMSM EDU used for the 1.4 pp comparison must be specified in detail (identical power rating, voltage, cooling, and control strategy) so that the efficiency delta can be reproduced and attributed unambiguously to the SMC-rotor combination.

Authors: We have expanded the description of the reference PMSM EDU in the revised manuscript, providing explicit details on the matched power rating, DC-link voltage, cooling system, and the field-oriented control strategy implemented in the EDU model to enable direct comparison. revision: yes

standing simulated objections not resolved

Hardware validation or calibration of the FEA models and resulting efficiency predictions

Circularity Check

0 steps flagged

No significant circularity; efficiency from standard FEA on evaluated material sets

full rationale

The paper evaluates multiple SMC materials and lamination thicknesses via finite-element analysis, identifies the optimal SMC-stator/0.35 mm NO35 rotor pair by comparing simulated torque and loss maps, then integrates those maps into an EDU model to compute WLTP-cycle efficiency. No equations, parameters, or claims reduce the reported 89.7 % figure or the 1.4 pp gain to a fitted quantity defined by the same data, a self-citation chain, or an ansatz smuggled from prior work. The derivation relies on conventional simulation workflows without self-definitional loops or uniqueness theorems imported from the authors' own prior publications.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard electromagnetic finite-element modeling assumptions and tabulated material properties; no new physical entities or ad-hoc constants are introduced.

free parameters (2)

rotor lamination thickness
0.35 mm NO35 selected after comparative evaluation of several thicknesses
SMC grade
Optimal grade chosen after testing multiple commercial SMC materials

axioms (2)

domain assumption Finite-element analysis with standard loss models accurately captures torque and efficiency under WLTP conditions
Invoked for all reported performance numbers
domain assumption Material B-H curves and loss coefficients supplied by manufacturers are representative of the final manufactured parts
Used as input to the simulations

pith-pipeline@v0.9.0 · 5495 in / 1456 out tokens · 37986 ms · 2026-05-08T07:09:31.569615+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

12 extracted references · 9 canonical work pages

[1]

El Hajji, A

A. Carlsson, F. Andersson, I. Santantonio, V . Josefsson, G. Puccio, and S. Rubino. Perfor- mance and efficiency mapping of externally excited synchronous machines. In2024 Inter- national Conference on Electrical Machines (ICEM), pages 1–7, Torino, Italy, 2024. doi: 10.1109/ICEM60801.2024.10700343

work page doi:10.1109/icem60801.2024.10700343 2024
[2]

Santantonio, S

I. Santantonio, S. Nategh, A. Carlsson, G. Franceschini, P. Farah, and D. Zefack. High-frequency rotor excitation system Part I: Modeling method and optimization. In 2023 AEIT International Conference on Electrical and Electronic Technologies for Au- tomotive (AEIT AUTOMOTIVE), pages 1–6, Modena, Italy, 2023. doi: 10.23919/ AEITAUTOMOTIVE58986.2023.10217231

work page arXiv 2023
[3]

El Hajji, S

T. El Hajji, S. Hlioui, F. Louf, M. Gabsi, G. Mermaz-Rollet, and M. Belhadi. Optimal de- sign of high-speed electric machines for electric vehicles: A case study of 100 kw v-shaped interior PMSM.Machines, 11(1):57, 2023. doi: 10.3390/machines11010057

work page doi:10.3390/machines11010057 2023
[4]

Mademlis, Y

G. Mademlis, Y . Liu, J. Tang, L. Boscaglia, and N. Sharma. Performance evaluation of elec- trically excited synchronous machine compared to PMSM for high-power traction drives. In 2020 International Conference on Electrical Machines (ICEM), pages 1793–1799, Gothen- burg, Sweden, 2020. doi: 10.1109/ICEM49940.2020.9270852

work page doi:10.1109/icem49940.2020.9270852 2020
[5]

Santantonio, S

I. Santantonio, S. Nategh, G. Franceschini, and D. Zefack. High-frequency rotor excitation system Part II: Material selection. In2023 AEIT International Conference on Electrical and Electronic Technologies for Automotive (AEIT AUTOMOTIVE), pages 1–6, Modena, Italy,
[6]

doi: 10.23919/AEITAUTOMOTIVE58986.2023.10217199. 14

work page doi:10.23919/aeitautomotive58986.2023.10217199 2023
[7]

El Hajji, A

Branko Ban, Anton Kersten, Stefan Skoog, Lars Sjöberg, Stjepan Stipeti ´c, and Tushar Batra. Comparative analysis of electric motor designs: Traditional steel laminations vs. soft mag- netic composite materials. In2024 International Conference on Electrical Machines (ICEM), pages 1–8, 2024. doi: 10.1109/ICEM60801.2024.10700236

work page doi:10.1109/icem60801.2024.10700236 2024
[8]

Krings, M

A. Krings, M. Cossale, A. Tenconi, J. Soulard, A. Cavagnino, and A. Boglietti. Magnetic materials used in electrical machines: A comparison and selection guide for early machine design.IEEE Industry Applications Magazine, 23(6):21–28, 2017. doi: 10.1109/MIAS.2016. 2600721

work page doi:10.1109/mias.2016 2017
[9]

Hoganas.com

Höganäs AB. Hoganas.com. Online. URLhttps://www.hoganas.se/
[10]

Krings, A

A. Krings, A. Boglietti, A. Cavagnino, and S. Sprague. Soft magnetic material status and trends in electric machines.IEEE Transactions on Industrial Electronics, 64(3):2405–2414,
[11]

doi: 10.1109/TIE.2016.2613844

work page doi:10.1109/tie.2016.2613844 2016
[12]

El Hajji, A

T. El Hajji, A. Lehikoinen, A. Hemeida, and A. Belahcen. Optimal design of cost-effective e-machines for traction: A case study of 150kw v-shaped PMSM. In2024 International Conference on Electrical Machines (ICEM), pages 1–5, Torino, Italy, 2024. doi: 10.1109/ ICEM60801.2024.10700405. 15

work page arXiv 2024