Magnetic Equivalent Circuit Modeling of the AC Homopolar Machine for Flywheel Energy Storage

Eric Severson, Robert Nilssen, Tore Undeland, Ned Mohan

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


This paper develops a magnetic equivalent circuit model suitable to the design and optimization of the synchronous ac homopolar machine. The ac homopolar machine is of particular interest in the application of grid-based flywheel energy storage, where it has the potential to significantly reduce self-discharge associated with magnetic losses. The ac homopolar machine features both axial and radial magnetizing flux paths, which requires finite element analysis to be conducted in 3-D. The computation time associated with 3-D finite element modeling is highly prohibitive in the design process. The magnetic equivalent circuit model developed in this paper is shown to be a viable alternative for calculating several design performance parameters and has a computation time which is orders of magnitude less than that of 3-D finite element analysis. Results obtained from the developed model are shown to be in good agreement with finite element and experimental results for varying levels of saturation.

Original languageEnglish (US)
Article number7134770
Pages (from-to)1670-1678
Number of pages9
JournalIEEE Transactions on Energy Conversion
Issue number4
StatePublished - Dec 2015


  • Energy storage
  • finite element analysis
  • flywheels
  • magnetic equivalent circuit (MEC)
  • renewable generation

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