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Title: Rare-earth free multi-phase motor with fault tolerant control

Authors: Sai Sudheer Reddy Bonthu, Md. Zakirul Islam, A.K.M. Arafat, Seungdeog Choi

Abstract: Recent studies on multi-phase electric motors have proven that the addition of redundant phases to a conventional three-phase electric motor increases the fault tolerant capability of the motor which provides safer and reliable operation. Moreover, the torque pulsations are significantly low in the multi-phase electric motors. For critical applications such as electric vehicles (EVs), mining haul trucks, naval, aerospace and military vehicles where efficiency, safety, and reliability are top priority, multi-phase permanent magnet motors are the best fit. Conventionally, to develop high torque and efficiency, permanent magnet motors use rare-earth materials such as neodymium (Nd) and samarium (Sm) which are less abundant and more expensive compared to the ferrite magnets. In this study, the design and control of a rare-earth material free multi-phase electric motor (FMEM) is presented. Detailed analytical and finite element methods to develop the optimal design of the FMEM are discussed. Initially, a five-phase FMEM with ferrite magnet assisted synchronous reluctance motor (Fa-SynRM) architecture is designed. Thorough electromagnetic, structural and thermal analyses have been conducted on the design in finite element (FE) environment. After the effectiveness of the 3-dimensional FE model is validated, the optimal design of FMEM has been tested for its fault tolerant capability using advanced field oriented control. Motor performance under various types of open-phase fault conditions has been investigated. With maximizing the developed torque as objective, current phase advance technique to provide optimal set of currents for respective fault conditions has been proposed for the developed FMEM. Under various open phase fault conditions, the torque developed and torque pulsations have been compared with the healthy motor. It has been observed that the proposed FMEM is fault tolerant under single phase, two phase adjacent and non-adjacent fault conditions.