An Investigation into the Saliency Ratio of Fractional-Slot Concentrated-Winding Generators for Offshore Wind Power

Isaac Rudden, Guang-Jin Li (), Zi-Qiang Zhu, Alexander Duke and Richard Clark
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Isaac Rudden: Electrical Machines & Drives Group, Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S10 2TN, UK
Guang-Jin Li: Electrical Machines & Drives Group, Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S10 2TN, UK
Zi-Qiang Zhu: Electrical Machines & Drives Group, Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S10 2TN, UK
Alexander Duke: Siemens Gamesa Renewable Energy Ltd., North Campus, Broad Lane, Sheffield S3 7HQ, UK
Richard Clark: Siemens Gamesa Renewable Energy Ltd., North Campus, Broad Lane, Sheffield S3 7HQ, UK

Energies, 2025, vol. 18, issue 8, 1-27

Abstract: This paper investigates the nature of the low saliency ratio of large permanent magnet generators with fractional-slot concentrated windings (FSCWs). A saliency ratio of at least 1.2 is typically required to enable sensorless control of large generators—a value naturally achieved in integer slot winding topologies but absent in FSCW surface-mounted permanent magnet machines reported in the literature. The low saliency ratio in FSCW designs is attributed to larger teeth, which reduce magnetic saturation and increase d -axis inductance. This work explores methods to enhance the saliency ratio of FSCW machines for offshore wind turbines, facilitating sensorless rotor position estimation. The proposed approaches are categorized into two groups: (1) those that preserve the conventional machine geometry with minimal modification to the magnetic circuit and (2) those involving magnetic circuit alterations. The results show that significant improvement in saliency ratio is only achievable through magnetic circuit modifications, such as rotor shoes, albeit with some performance trade-offs. A multi-objective genetic algorithm is employed to design two optimized 3 MW FSCW machine topologies, achieving saliency ratios of 1.15 and 1.2 with minimal performance loss. Compared to a 3 MW FSCW baseline, the optimized designs show stator power reductions of 3.40% and 6.16% for saliency ratios of 1.15 and 1.2, respectively.

Keywords: concentrated winding; fractional slot; saliency; sensorless; PM wind generators (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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