High-Frequency Litz “Air-Gap” Windings for High-Power Density Electrical Machines

Jonathan Martin, Andy Yoon, Austin Jin, Kiruba S. Haran

Research output: Contribution to journalArticlepeer-review


This paper describes the development of high-frequency air-gap windings for a 1 MW, 96% efficient permanent magnet (PM) motor, targeted at 13 kW/kg. Due to the power level and high-specific power requirements, special attention has to be paid to the electromagnetic, thermal, and mechanical performance for the high-frequency coils. Specifically, AC losses have to be minimized while fill factor and thermal conductivity of the assembly are maximized. The paper presents analytical and finite element-based AC loss studies along with experimental validation by indirect balanced calorimetry, and shares the results which should be scalable for other large machines. Hardware development and corresponding manufacturing process are also described.

Original languageEnglish (US)
Pages (from-to)798-805
Number of pages8
JournalElectric Power Components and Systems
Issue number7
StatePublished - Apr 21 2017


  • AC losses
  • Litz winding
  • air gap winding
  • high speed machines
  • permanent magnet motors
  • synchronous motors

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Mechanical Engineering
  • Electrical and Electronic Engineering

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