Prospects for Non-Rare Earth Permanent Magnets for Traction Motors and Generators

M J Kramer,S Constantinides,R W Mccallum,I A Anderson

doi:10.1007/s11837-012-0351-z

Abstract

With the advent of high-flux density permanent magnets based on rare earth elements such as neodymium (Nd) in the 1980s, permanent magnet-based electric machines had a clear performance and cost advantage over induction machines when weight and size were factors such as in hybrid electric vehicles and wind turbines. However, the advantages of the permanent magnet-based electric machines may be overshadowed by supply constraints and high prices of their key constituents, rare earth elements, which have seen nearly a 10-fold increase in price in the last 5 years and the imposition of export limits by the major producing country, China, since 2010. We outline the challenges, prospects, and pitfalls for several potential alloys that could replace Nd-based permanent magnets with more abundant and less strategically important elements.

Highlights

Transportation accounts for 28% of energy consumption in the United States,[1] of which 93% comes from petroleum
While biofuels and hydrogen can replace fossil fuels for use in internal combustion engines, electric motors in combination with an internal combustion engine or all-electric vehicles are seen as the primary technologies capable of reducing dependence on petroleum for the transportation sector
Since the advent of high-flux density permanent magnets based on rare earth elements such as neodymium (Nd) or samarium (Sm), permanent magnet-type electric machines* are preferred over induction machines when weight and size are factors, such as in hybrid electric vehicles.[2]

Summary

INTRODUCTION

Transportation accounts for 28% of energy consumption in the United States,[1] of which 93% comes from petroleum. The higher temperature performance requirement of generators and traction motors requires an adjustment to the Nd-based permanent magnets alloy to improve its high temperature resistance to demagnetization This is accomplished with the addition of heavy rare earth elements, primarily Dy. Dy, while reducing Br, provides a moderate increase in Tc and a significant increase in the anisotropy field, which helps maintain a useful HcJ at temperatures up to $200°C. While significant improvements have been made in preceding decades in the energy density for ferrites,[30] there are a number of significant intrinsic limitations for this class of compounds They have a very high mass-to-magnetization ratio so that the size of a permanent magnet-based electric machine would be too large for a hybrid vehicle. If means can be found to compensate for the detrimental properties of Ce, the availability of rare earth element magnets from existing sources could be greatly enhanced

Findings

DISCUSSION

CONCLUSIONS