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

ABSTRACT

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.

Keywords::

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

Funding

This work was supported in part by NASA (Grant NNX14AL79A) and the Grainger Center for Electric Machinery and Electromechanics at the University of Illinois Urbana-Champaign.

BIOGRAPHIES

Jonathan Martin obtained a B.A. in Physics from Colgate University in 2014 and completed his M.Sc. in Electrical Engineering under Professor Kiruba Haran at the University of Illinois Urbana-Champaign in May 2016. He is currently working for Intel Corporation based in Portland, OR. His research interests include high-power-density electric machines and ac-loss/electromagnetic analysis in electric machines.

Andy Yoon received B.S. in Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign in 2013. He is currently working with Professor Kiruba Haran toward the Ph.D. degree. His research interests include high-frequency, high-speed, power dense electric machines.

Austin Jin received B.S. in Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign in 2016. He is currently pursuing an M.S. degree in Electrical Engineering. His research interests include the application of superconductivity on electric machinery and machine design.

Kiruba S. Haran received the B.S. degree in electrical engineering from Obafemi Awolowo University, Ife, Nigeria, in 1994, and the Ph.D. degree in electric power engineering from Rensselaer Polytechnic Institute, Troy, NY, USA, in 2000. He was with GE Global Research Center, Niskayuna, NY, USA, for 13 years, first as an Engineer and then a Manager of the Electrical Machines Laboratory. In 2014, he moved to the University of Illinois, Champaign, IL, USA, to join the Grainger Center for Electric Machinery and Electromechanics and the Faculty of Electrical and Computer Engineering. His interest research include high specific power electric machines for aviation applications, superconducting machines, and diagnosis of synchronous machines.

Additional information

Notes on contributors

Jonathan Martin

Jonathan Martin obtained a B.A. in Physics from Colgate University in 2014 and completed his M.Sc. in Electrical Engineering under Professor Kiruba Haran at the University of Illinois Urbana-Champaign in May 2016. He is currently working for Intel Corporation based in Portland, OR. His fields of interest include high-power-density electric machines and ac-loss/electromagnetic analysis in electric machines.

Andy Yoon

Andy Yoon received B.S. in Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign in 2013. He is currently working with Professor Kiruba Haran toward the Ph.D. degree. His research interest includes high-frequency, high-speed, power dense electric machines.

Austin Jin

Austin Jin received B.S. in Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign in 2016. He is currently pursuing an M.S. degree in Electrical Engineering. His research interest includes the application of superconductivity on electric machinery and machine design.

Kiruba S. Haran

Kiruba S. Haran received the B.S. degree in electrical engineering from Obafemi Awolowo University, Ife, Nigeria, in 1994, and the Ph.D. degree in electric power engineering from Rensselaer Polytechnic Institute, Troy, NY, USA, in 2000. He was with GE Global Research Center, Niskayuna, NY, USA, for 13 years, first as an Engineer and then a Manager of the Electrical Machines Laboratory. In 2014, he moved to the University of Illinois, Champaign, IL, USA, to join the Grainger Center for Electric Machinery and Electromechanics and the Faculty of Electrical and Computer Engineering. His current research includes high specific power electric machines for aviation applications, superconducting machines, and diagnosis of synchronous machines.