Performance Modeling and Analysis of a Doubly Yokeless Permanent Magnet Linear Motor With Improved Thrust Force Quality

Permanent magnet linear motors (PMLM) have gained increased popularities in a wide range of applications. However, they generally suffer from considerably lower force densities. In this paper, a novel doubly yokeless PMLM equipped with quasi-Halbach trapezoidal-shape permanent magnets is presented to both increase the thrust force density and suppress the thrust ripple. Both the stator and the translator are yoke-free, and therefore, the increase of the installation space for the windings is conducive to enhancing the magneto-motive force and the thrust density of the motor. An analytical model is developed to predict the magnetic field distribution and electromagnetic performance of the doubly yokeless PMLM, and finite element computations are undertaken to validate the effectiveness and accuracy of the proposed model. The thrust performance is then optimized against magnet parameters under a specific set of volumetric constraints to the improve the thrust force quality. It is shown that the Halbach ratio and bottom angle of the trapezoidal magnets have significant impacts on the thrust force quality (in terms of both the average thrust and thrust ripple), and optimal values for the two parameters are obtained. The benefits of the doubly yokeless PMLM are highlighted by comparisons with a conventional PMLM with iron yokes.