Design Considerations of a Brushless Open-Slot Radial-Flux PM Hub Motor

Rafal Wrobel, James Goss, Adrian Mlot, Phil Mellor

Research output: Contribution to journalArticle (Academic Journal)peer-review

35 Citations (Scopus)


Initial sizing of a brushless radial-flux permanent- magnet (PM) machine is typically based on assumptions regard- ing the electric and magnetic loadings together with the motor’s active volume. Additional design assumptions include the winding current density and magnetic flux density within the core pack. These initial design decisions are crucial as they largely define the resultant electromagnetic and thermal behaviors of the motor. The general rules regarding the choice of the initial design parameters are well known. However, the effects of the initial sizing on the final motor performance are not widely reported. This paper presents an analysis of the design considerations for a brushless open-slot radial-flux PM hub motor. A number of alternative motor designs are compared to demonstrate the effect of the initial design deci- sions on the final motor performance. Both electromagnetic and thermal aspects of the motor design are considered. The design variants are characterized by the same electric and magnetic load- ings together with active volume while the winding rated current density and no-load/open-circuit magnetic flux density within the core pack are varied. The employed sizing methodology com- bines the classical approach with a nonlinear magnetostatic finite- element solver and an optimization routine. A prototype hub motor has been manufactured to validate the theoretical findings from the design process. The experimental data show good agree- ment with the theoretical findings.
Original languageEnglish
Pages (from-to)1757 - 1767
Number of pages11
JournalIEEE Transactions on Industry Applications
Issue number3
Publication statusPublished - 15 May 2014


  • AC motors
  • brushless motors
  • motor design
  • motor sizing
  • open-slot radial-flux motor topology
  • permanent- magnet motors


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