Identification and Reduction Method of Normal-Direction Force Ripple in Permanent Magnet Linear Synchronous Motor

In this paper, we present identification methods of normal-direction motor parameters and a force ripple reduction method in the normal direction for permanent-magnet linear synchronous motors (PMLSMs). This paper discusses the force generation mechanism of a PMLSM both in the normal and tangential directions by the D- and Q-axis currents, which is utilized for identifying and suppressing the motor force ripple in the normal direction. Using the proposed identification method on the experimental setup of a linear stage driven by an iron-cored PMLSM, we identify the normal-direction force constant with an error of only 7% as compared to a direct measured data from a dynamometer. The geometry-driven ripple in the normal direction is also identified by experimentally estimating the dominant 2nd-and 6th-order spatial harmonics, which also show significant fidelity with an NRMSE (peak-to-peak normalized root-mean-square error) of only 3.39% as compared to the dynamometer measurement. Using the identified motor parameters, we achieve the force ripple reduction in the normal direction by 84.6% and 87.8% in peak-to-peak and root-mean square (RMS) values, respectively.