Defining the Magnetization State of LCF Magnets: From Material Properties to Motor-Level Metrics

TL;DR

This paper introduces four magnetization state definitions for LCF magnets, linking material properties to motor-level metrics, evaluated via finite element analysis for improved motor control and analysis.

Contribution

It proposes a unified framework for defining and comparing magnetization states across material and motor levels, aiding in motor design and control.

Findings

Four magnetization state definitions evaluated across operating planes.

Finite element analysis clarifies the relationship between material and motor quantities.

Guidelines provided for selecting MS metrics based on application needs.

Abstract

Variable flux memory motors, which employ Low Coercive Force (LCF) magnets, achieve extended high-efficiency operation through controllable magnetization states. To address the need for a unified approach to defining and comparing the magnetization state (MS) across material and motor levels, this paper proposes four MS definitions: two based on intrinsic material properties-magnetic flux density B and magnetic polarization J-and two based on motor-level quantities-fundamental flux linkage and back-EMF components. These definitions are evaluated across the id, iq operating plane using finite element analysis on an interior PMSM with a hybrid magnet configuration (LCF and HCF: High Coercive Force) and a defined circuit setup. The results clarify the relationship between material-level behavior and measurable motor quantities. The proposed framework provides guidance for selecting appropriate MS metrics depending on the application objective, whether for material analysis, control implementation, or condition monitoring in variable flux machines.