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Lookup NU author(s): Dr Saleh AliORCiD, Dr Farshid Mahmouditabar, Professor Volker PickertORCiD, Dr Shafiq OdhanoORCiD, Dr Muhammad Awan, Dr Zepeng LiuORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Magnetless rotary transformer excitation systems enable fully brushless operation of electrically excited synchronous machines (EESMs) and offer a scalable alternative to permanent-magnet drives. This review presents a control-oriented synthesis of rotary-transformer-excited EESMs by linking machine topology, modeling methods, resonant compensation networks, inverter architectures, and excitation-control strategies within a unified framework. The paper outlines a complete modeling chain, from fundamental-harmonic approximation to dynamic direct-quadrature-axis and coupled electromagnetic-thermal analysis, to support accurate field-current regulation and efficiency optimization. Inverter and compensation networks that enable soft switching are compared in terms of controllability, voltage regulation, efficiency, and implementation complexity. Emerging self-excitation methods, including common-mode voltage injection, harmonic excitation, and carrier-phase modulation are also assessed with respect to implementation simplicity and control flexibility. The review concludes by identifying key challenges in sensorless excitation control, thermal coupling, and high-frequency operation, and by highlighting research directions that can further enhance the performance, reliability, and scalability of brushless EESM drives.
Author(s): Ali SA, Mahmouditabar F, Pickert V, Odhano S, Awan M, Liu Z
Publication type: Article
Publication status: Published
Journal: IEEE Access
Year: 2026
Pages: epub ahead of print
Online publication date: 20/05/2026
Acceptance date: 14/05/2026
Date deposited: 01/06/2026
ISSN (electronic): 2169-3536
Publisher: IEEE
URL: https://doi.org/10.1109/ACCESS.2026.3695371
DOI: 10.1109/ACCESS.2026.3695371
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