Semianalytical Calculation of the Torque in a Linear Permanent-Magnet Motor With Finite Yoke Length

In this paper, a semianalytical model for the calculation of the torque produced by an iron-cored linear permanent-magnet motor is presented. The torque is calculated by means of the Maxwell stress tensor, which requires a description of the magnetic flux density distribution. The two-dimensional distribution is obtained from a semianalytical harmonic model, which accounts for the slotting and finite length of the iron yoke. An analytical expression for the thrust and normal force is obtained by evaluating the Maxwell stress tensor over a line through the air gap. For the torque calculation, the Maxwell stress tensor is numerically integrated along a contour that closely follows the structure of the yoke. The resulting torque and forces show good agreement with finite-element (FE) results.