This paper deals with the effects of permanent magnets (PMs) shapes and segmentation types on the trapezoidal degrees of the back electromagnetic force (EMF) and torque characteristics and rotor losses. The back-EMF waveforms with different PMs shapes and segmentation types are calculated through transient finite element method (FEM). It is found that the effects of PMs inward eccentricity and curvature have no influence on the shape of the back-EMF waveforms. The PMs asymmetrical segmentation

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... ith the middle sub-PMs applied with low magnetic energy product sintered ferrite magnet can obtain better trapezoidal back-EMF waveforms. Then, the torque characteristics and rotor losses of PMs' symmetrical and asymmetrical segmentations are investigated and evaluated. The results show that the PMs segmentation and applying low magnet energy product PMs of the middle sub-PMs can further improve the torque characteristics. Moreover, the outer PMs eddy current loss and rotor iron loss exhibit a great extent of decrement. Finally, a stator-ironless PM BLDC motor without the outer rotor PMs segmentation is manufactured and tested. The experimental results show good agreement with the FEM ones. INDEX TERMS Stator-ironless, brushless DC (BLDC) motor, non-ideal back-EMF, rotor eddy current loss, permanent magnets (PMs) shape. 28044 2169-3536 2019 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. VOLUME 7, 2019 LIU YANG received the B.E. degree in machine design manufacture and automation from the Inner Mongolia University of Technology, Hohhot, China, in 2012, and the M.Sc. degree in mechanical electronic engineering from Harbin Engineering University, Harbin, China, in 2015. He is currently pursuing the Ph.D. degree with the School of Automation, Beijing Institute of Technology, Beijing, China. His research interests include modeling and design of PM machines, and high-precision servo control for positioning systems.