Rotor Eddy Current Loss Reduction with Permeable Retaining Sleeve for Permanent Magnet Synchronous Machine

Zichong Zhu*, Yunkai Huang, Jianning Dong, Fei Peng, Yu Yao

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

20 Citations (Scopus)
445 Downloads (Pure)


This article presents a new rotor design to reduce rotor eddy current loss of a high-speed permanent magnet synchronous machine for flywheel energy storage system. Instead of using common nonmagnetic sleeves, the new rotor incorporates permeable retaining sleeves (PRSs) to fix permanent magnets on the rotor hub. The PRSs are made of permalloy that features high permeability and high electrical conductivity. Thus, skin depths for asynchronous harmonics are extremely small. On the other hand, the PRSs are electrically insulated along the circumferential direction. Owing to these two reasons, rotor eddy current loss at open circuit decreases by 64.2% without sacrificing torque output, compared with an original rotor with nonmagnetic retaining sleeve. In addition, thermal and structural finite element analyses are performed to calculate rotor temperature distribution and evaluate the structural integrity of the new rotor. Rotor eddy current loss reduction benefits lowering rotor temperature rise. Prototype machine with the new rotor is fabricated, and preliminary tests are carried out to confirm the analysis results.

Original languageEnglish
Article number8959123
Pages (from-to)1088-1097
Number of pages10
JournalIEEE Transactions on Energy Conversion
Issue number2
Publication statusPublished - 1 Jun 2020

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • Eddy current
  • high-speed machine
  • permanent-magnet machine
  • permeable retaining sleeve (PRS)
  • rotor loss reduction


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