Analysis of air-gap field modulation and magnetic gearing effects in switched flux permanent magnet machines

Z. Z. Wu, Z. Q. Zhu

Research output: Contribution to journalArticlepeer-review

238 Citations (SciVal)


In this paper, switched flux permanent magnet (SFPM) machines are analyzed from the perspective of the air-gap field harmonics. It is found that the modulation of the salient rotor to PM and armature reaction fields in SFPM machines is similar to that of the iron pieces to those fields in the magnetic gear and magnetically geared machine. The magnetic gearing effect is analyzed in SFPM machines with different stator/rotor pole combinations, winding configurations, and stator lamination segment types by a simple magnetomotive force-permeance model, and validated by finite-element (FE) analysis. Different from fractional-slot surface-mounted PM machines in which the working air-gap field harmonic generates >95% of the average electromagnetic torque, >95% of the average electromagnetic torque in SFPM machines having \boldsymbol {p}-{\boldsymbol {s}} stator pole pairs and n-{r} rotor poles are contributed by several dominating field harmonics, i.e., rotating ones with \vert kn-{\boldsymbol {r}}\,\pm \, (\textbf {2}\boldsymbol {i}-\textbf {1})\boldsymbol {p}-{\boldsymbol {s}}\vert pole pair ( \boldsymbol {k}=\textbf {1}, \boldsymbol {i}=\textbf {1, 2, 3} ) and static ones with (2\boldsymbol {i}-\textbf {1})\boldsymbol {p}-{\boldsymbol {s}} pole pair ( \boldsymbol {i}=\textbf {1, 2, 3} ). The FE predicted average static torques in SFPM machines are validated by measurements on prototype machines.

Original languageEnglish
Article number7038147
Pages (from-to)1-12
Number of pages12
JournalIEEE Transactions on Magnetics
Issue number5
Early online date10 Feb 2015
Publication statusPublished - 1 May 2015


  • Flux switching
  • harmonic analysis
  • magnetic gear
  • magnetic gearing effect
  • magnetically geared machine
  • modulation
  • permanent magnet machines
  • switched flux

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering


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