Thrust Ripple of a Permanent Magnet LSM With Step Skewed Magnets

This paper analyzes the thrust characteristics of the investigated permanent magnet linear synchronous motor (PMLSM) and discusses their differences with those of rotary motors. It shows that the main components of the thrust ripple are second, fourth, and sixth harmonics, which is produced by end-effect, not the 12th harmonic caused by cogging. The ripple suppression abilities of magnet step-skew method are analyzed through skew factors of thrust harmonics and effective electromagnetic thrust. The optimal step number and skew angle for PMLSM are studied with comparison to those of rotary motor. A 2-D FEM algorithm for the asymmetric PMLSM model analysis is investigated, with which the aforesaid skew step number selection and optimal skew angle are validated.

I. Introduction

Permanent magnet linear synchronous motor (PMLSM) is adopted by some high-speed digital machine because of its evident advantages such as high acceleration, excellent accuracy and direct drive [1]. With the armature of iron core, it could not only output higher thrust but also bring in higher thrust ripple. So the ripple suppression is vital for PMLSM design.