Testing and Characterisation of a Reduced Rare‐Earth PM‐Assisted Synchronous Reluctance Machine Using Dysprosium‐Free NdFeB and Ferrite Magnets

ABSTRACT

Reducing rare‐earth (RE) content in an electric vehicle (EV) traction motor whilst preserving performance and demagnetisation resistance remains a major challenge. This paper presents the design, optimisation, manufacturing and experimental validation of an OEM‐scale Permanent Magnet Assisted Synchronous Reluctance Machine (PMASynRM) developed as a reduced‐RE retrofit solution for a Chevy‐Bolt EV traction motor. The key contributions of this work include: (1) development of a hybrid magnet PMASynRM rotor utilising Dy‐free NdFeB and ferrite magnets, enabling complete elimination of heavy rare‐earth (Dysprosium) element, (2) implementation of a multi‐objective design optimisation framework incorporating electromagnetic torque, demagnetisation risk, torque ripple, voltage limits and mechanical stress to obtain a manufacturable high‐speed rotor design, (3) achievement of 26% reduction in light rare‐earth (NdFeB) magnet volume through design optimisation, (4) development of a retrofit‐ready rotor compatible with the existing Chevy‐Bolt interior permanent magnet (IPM) motor stator, whilst maintaining performance comparable to the original motor, (5) comprehensive experimental validation of the full‐scale prototype under realistic operating conditions, including flux‐map evaluation, torque‐speed characterisation, power‐loss and efficiency measurements and demagnetisation test under severe negative d‐axis current excitation and elevated temperatures. Experimental results show good agreement with Finite Element Analysis (FEA) predictions and demonstrate the feasibility of reduced rare‐earth and heavy‐rare‐earth‐free PMASynRMs for high‐performance EV traction motor applications.