Rare-earth permanent magnets (RE-PMs) are widely used in high-efficiency and high-torque density electrical machines. However, in recent years, the exclusive and unstable supply of rare-earth elements (REEs) is a major concern to substitute RE-based electrical machines by less or even no RE alternatives. Ferrite (Fe) PMs as the least expensive PMs show promising opportunities for designing low-cost non-RE electrical machines. This article reviews some relevant works on Fe-based machines, which generally have been conducted to replace RE-based machines. Fe-based machines, including PM brushless, PM-assisted synchronous reluctance, PM flux switching, and PM Vernier machines, are introduced and their main design challenges, such as low PM energy product and vulnerability to irreversible demagnetization, are addressed. In addition, a comparison of RE- and Fe-based machines reveals that when both cost and efficiency are the major concerns, Fe-based machines can be a good successor to RE-based machines.

中文翻译：

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电机中的铁氧体永磁体：非稀土替代品的机遇和挑战

稀土永磁体 (RE-PM) 广泛应用于高效率和高扭矩密度的电机中。然而，近年来，稀土元素 (REE) 的独家和不稳定供应是用较少甚至没有 RE 替代品替代基于 RE 的电机的主要问题。铁氧体 (Fe) PM 作为最便宜的 PM，显示出设计低成本非 RE 电机的广阔前景。本文回顾了一些关于 Fe 基机器的相关工作，这些工作通常是为了替代 RE 基机器而进行的。介绍了基于铁的电机，包括永磁无刷、永磁辅助同步磁阻、永磁磁通开关和永磁游标电机，并解决了它们的主要设计挑战，例如低 PM 能量积和不可逆退磁的脆弱性。此外，