Advanced High Torque Density PM Vernier Machine With Multiple Working Harmonics

In recent years, permanent magnet (PM) vernier machines have gained more and more attention due to their high torque density and simple mechanical structure. However, PM vernier (PMV) machines with lap windings always suffer from long end winding length, and regular nonoverlapping winding may result in torque reduction for PMV machines. In this paper, an advanced PMV machine topology with multiple working harmonics is proposed. With specially designed stator auxiliary teeth, this topology could achieve ~20% higher torque density than that of a regular nonoverlapping winding PMV machine, with the same magnet usage. Through finite element algorithm and theoretical analysis, the production of additional flux density harmonics and their contributions to back-electromotive force (EMF) are verified. Moreover, the electromagnetic performances of this novel machine topology, such as back-EMF and output torque, are quantitatively investigated with the geometric parameters' effect considered. Finally, analysis results are verified by experimental test on a 21 Nm prototype, which is designed to have similar volume and weight with a 14 Nm regular commercial PM machine.

I. Introduction

With the advantages of high reliability, low vibration, and noise, direct drive machines have been more and more popular in industry applications, such as wind generator, ship propulsion, machine tool, etc. However, direct drive machines always suffer from large weight and volume due to high torque demand, which has become a key barrier for their application extension. Hence, the high torque density machines have been attracting more and more attentions. In recent years, permanent magnet (PM) vernier machines are more and more widely researched due to their superior torque density and simple mechanical structure.