NDLI: Design trade-off between cogging torque and torque ripple in fractional slot surface-mounted permanent magnet machines

Content Provider	IEEE Xplore Digital Library
Author	Wu, D. Zhu, Z.
Copyright Year	2015
Description	Author affiliation: Electron. & Electr. Eng., Univ. of Sheffield, Sheffield, UK (Wu, D.; Zhu, Z.)
Abstract	Summary form only given. In designing the fractional slot surface-mounted permanent magnet (SPM) machines for servo and direct-drive applications, the cogging torque and on-load torque ripple are both major design considerations. Nevertheless, since the torque ripple depends on load conditions, the optimal tooth-tip design for the smallest cogging torque may not be the same for the smallest torque ripple as well. Usually cogging torque will reduce with slot opening width $(b_{0})$ [1] as shown in Fig.1(a). However, the variations of torque ripple are more complicated. With the help of frozen permeability method [2], the on-load torque can be seen as composed by PM torque $(T_{PM}),$ reluctance torque $(T_{r})$ and on-load cogging torque $(T_{cog}),$ which all contribute to torque ripple, Fig.1(b). The variation of these components against different $b_{0}$ under full-load are shown in Figs.1(c) and (d). It can be seen that the average torque for $T_{r}$ will not be zero even in SPM machines due to cross-coupling saturation. With the reducing of $b_{0},$ the leakage flux will increase, which reduces the average torque and makes the fluctuations of $T_{cog}$ even increase under full-load condition. However, under half-load condition, the variation of torque components against $b_{0}$ is totally different, Figs.1(e) and (f). It reveals that the cross-coupling effect under half-load becomes unobvious while $T_{cog}$ reduces when $b_{0}$ is small. Therefore, a trade-off exists in designing the tooth-tips for SPM machines . By way of example, if a SPM machine mainly works under idle (no-load) and low load conditions, the closed slot opening can be adopted since it will result in low open-circuit cogging torque as well as relative low torque ripple under low load conditions . A prototype machine with 12-slot/8-pole has been designed, analyzed and tested according to this application as shown in Figs .2(a) and (b) . Since the predicted cogging torque is extremely small, the experimental error may cover the real data . However, the amplitude of measured result still proves the tiny cogging torque . Meanwhile, the measured on-load torque validates the small torque ripples for low load regions .
Starting Page	1
Ending Page	1
File Size	645333
Page Count	1
File Format	PDF
e-ISBN	9781479973224
DOI	10.1109/INTMAG.2015.7157400
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2015-05-11
Publisher Place	China
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Torque Forging Permanent magnet machines Permeability Torque measurement Electrical engineering Permanent magnets
Content Type	Text
Resource Type	Article

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