Identification-Based Simultaneous Reduction of Tangential and Normal Force Ripples in PMLSMs Under Dynamic Operation

The iron-cored permanent-magnet linear synchronous motors (PMLSMs) are increasingly in demand with advantage of high force density and direct-drive capability. However, inherent force ripples caused by the magnetic saliency not only degrade the servo accuracy, but also induce vibration and noise, particularly during high-acceleration operations. This article presents a control-based force ripple reduction method to address such issues, by adjusting DQ-currents to counteract both tangential- and normal-direction force ripples simultaneously. Using an established motor force model, compensation DQ-currents are derived to generate additional forces that actively cancel out the force ripples. To enable effective compensation, experimental identification methods are developed to determine the force parameters required for the ripple reduction method, achieving a maximum identification error of less than 10 %. With these identified parameters, the proposed method experimentally achieves a reduction of over 87 % in the RMS value of tangential-direction force ripple and 69 % in the normal direction, all while maintaining constant motor thrust.