A Comprehensive Investigation of Low-Cost Permanent Magnet Machines with Ferrite Magnets and Enhanced Magnetic Loading

Abstract

Low-cost ferrite permanent magnet (PM) machines are promising alternatives to conventional machines that rely on expensive rare-earth PMs (RE-PMs). However, the inherently low energy density of ferrite PMs leads to reduced magnetic loading, posing a significant challenge in achieving comparable power density and compact machine size. To address this, specialized rotor pole configurations tailored to the characteristics and limitations of ferrite PMs are necessary. This study presents a comprehensive investigation and comparison of four rotor topologies featuring enhanced magnetic loading through the use of the flux focusing effect. The presented configurations include: (1) spoke-type poles, (2) combined spoke-type and V-shaped poles, (3) double V-shaped poles, and (4) multi-stage flux barrier poles. To ensure a fair comparison, all designs are optimized to maximize torque under identical armature design, current density, air-gap length, etc. The topologies are evaluated in terms of air-gap flux density, open circuit back-emf, torque-speed characteristics, and efficiency across a wide torque-speed range. To validate the simulation results, a ferrite PM machine is prototyped and experimentally tested.