Mohd Ab Halim, Mohd Firdaus (2022) Hybrid-excited magnetic gear employing rotating-pole-piece topology with improved gear efficiency for electric vehicle application. Doctoral thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

Magnetic gear (MG) is an attractive option to mechanical gear due to its contactless nature, which contributes to lower losses and higher efficiency. Different types of MG, differs in physical construction. Concentric magnetic gear (CMG) exhibits the highest torque production compared with other MGs. Yet, CMGs are generally analysed in low-speed applications due to eddy current loss from the permanent magnet (PM) during high-speed operations. This loss leads to decrease in output torque and gear efficiency. To overcome these in high-speed applications, as in electric vehicles (EVs), a different CMG topology known as rotating-pole-piece magnetic gear (RPMG) is more practical. RPMGs have fewer number of poles and hence higher transmitted torque and efficiency, although claimed to cause higher torque ripple than CMGs in some pole pair combinations. Therefore, in this work, torque characteristics were evaluated in RPMGs for several pole pair combinations and compared with the CMG topology. The second combination of gear ratio 7.66 was found to be the most practical option due to its lower number of pole pairs and 1% of torque ripple produced. Next, to improve gear efficiency, three strategies are considered and compared with the original RPMG. The strategies are lowering PM residual magnetic flux density level, performing rotor skewing and employing second flux source to the RPMG, which then transformed the RPMG into a hybrid-excited magnetic gear (HMG). Results gathered reveals that the HMG strategy produced the best improvement. To optimize the gear efficiency produced further, stator slot and tooth design of the HMG structures is improved, thus producing two other different variants; HMG C1 and HMG C5 and analysed using 2D finite element method. Gear efficiency achieved by the proposed HMG structures were above 96%. Meanwhile, the torque densities are above 200 kN.m/m3. These numbers are the highest if compared with previous studies. The newly proposed HMG structure has shorter flux path to the air gap and utilised smaller PM volume. It is hoped that the torque density and gear efficiency produced will elevate the overall performance of the drive system in EVs

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