Design of a Robust Five-Phase Ferrite-Assisted Synchronous Reluctance Motor With Low Demagnetization and Mechanical Deformation

This study presents the design of a robust five-phase ferrite (Fe) permanent-magnet-assisted synchronous reluctance motor (PMaSynRM) to mitigate two major design challenges: irreversible demagnetization and mechanical deformation. Recently, rare-earth magnet-based five-phase PMaSynRMs have been proposed for vehicular applications due to their better fault tolerance, higher torque density, and low torque ripple compared to their three-phase counterparts. However, rare-earth magnets are expensive and, their supplies were disrupted multiple times in past few years. Therefore, to avoid rare-earth magnets in traction motors, this study proposes a five-phase PMaSynRM with Fe magnet. Special attention is paid to avoid irreversible demagnetization and deformation as these are two major concerns in any Fe-based machine. The rotor structure is uniquely optimized with additional geometrical parameters to reduce the risk of irreversible demagnetization. To increase the structural stability of the rotor, optimal center post and weight reduction notches are adopted. The proposed Fe-based five-phase PMaSynRM has been comparatively studied over a rare-earth magnet-based PMaSynRM. The lumped parameter model and finite element model have been utilized for design optimization and performance analysis. Finally, A 3 kW prototype of the proposed five-phase Fe PMaSynRM has been fabricated, experimentally tested, and compared with the benchmark rare-earth PMaSynRM to validate the proposed design and simulations results.

I. Introduction

With the alarming rate of rises in oil prices and polar temperatures, fuel-efficient and environment-friendly electric and hybrid electric vehicles are gaining more popularity [1], [2]. Hence the automobile industry is investing more in innovative electric motor designs to get efficient, reliable, and low-cost drives for the next generation electric vehicles. Recently, rare-earth (RE) magnet free electric machines have become a popular research topic due to the higher expense and supply disruption of the rare-earth materials [3], [4]. Among RE-free designs, the five-phase ferrite permanent magnet assisted synchronous reluctance motor (Fe-PMaSynRM) has been a promising candidate for vehicular applications due to its low-cost, high torque density, high fault tolerance capability and low torque ripple [5]–[7]. However, due to significantly low intrinsic coercive force and energy density, ferrite-based machines encounter several challenges including the risk of irreversible demagnetization, and mechanical deformation [8].