Rare-earth-free propulsion motors for electric vehicles: A technology review

Abstract

Several factors including fossil fuels scarcity, prices volatility, greenhouse gas emissions or current pollution levels in metropolitan areas are forcing the development of greener transportation systems based on more efficient electric and hybrid vehicles. Most of the current hybrid electric vehicles use electric motors containing powerful rare-earth permanent magnets. However, both private companies and estates are aware of possible future shortages, price uncertainty and geographical concentration of some critical rare-earth elements needed to manufacture such magnets. Therefore, there is a growing interest in developing electric motors for vehicular propulsion systems without rare-earth permanent magnets. In this paper this problematic is addressed and the state-of-the-art of the electric motor technologies for vehicular propulsion systems is reviewed, where the features required, design considerations and restrictions are addressed.

PM-Assisted Synchronous Reluctance Machine Flux Weakening Control for EV and HEV Applications

“…However, these technologies require high density magnetic materials to produce the rotor flux, usually sintered neodymium-iron-boron (NdFeB) alloys, and other rare-earth materials, such as dysprosium (Dy), leading to high price, risk of depletion and resource monopoly issues [2], [3]. For these reasons, alternative technologies that do not rely on these PM materials are attracting considerable attention, such as Switched Reluctance Machines (SRMs) [4], [5] and Induction Machines (IMs) [6].…”

“…Among them, Synchronous Reluctance Machines (SynRMs) can be highlighted due to their high temperature operation capability, high efficiency, and small [7] (usually ferrite magnets) or eventually non use of PMs [8]. These features make the SynRMs one of the most promising candidates for the next generation of EV and HEV [3]. According to [9], modern ferrite PM-Assisted machines can produce 75 % of the torque of an Interior PMSM for the same size and liquid cooling technology.…”

Detection of Eccentricity Faults in Five-Phase Ferrite-PM Assisted Synchronous Reluctance Machines

“…In recent years, SynRMs (synchronous reluctance machines) have become popular because of the volatility of the rare-earth PM (permanent magnet) price, concerns about the risk of supply [1], or the demand of highly-efficient machines. These factors are promoting SynRMs and ferrite-PM assisted SynRMs (fPMa-SynRMs) to be competitors of induction machines [2] and PM synchronous machines [3] in many applications requiring a high efficiency and torque density, wide constant-power speed range or overload capability [4].…”

Thermal-Flow Analysis of a Simple LTD (Low-Temperature-Differential) Heat Engine

“…If conversion efficiency is more important than power output, heat engines that operate on the Stirling cycle or its variations are more promising to approach the maximum possible efficiency predicated by the second law of Thermodynamics [1]. Theoretically, the conversion efficiency from mechanical energy to electricity can be 100% [4].…”