Force Ripple Modeling and Minimizing of an Ironless Permanent-Magnet Linear Synchronous Motor

A force ripple model considering both non-ideal magnetic field and windings was developed to study methods for the suppression of the force ripple in an ironless permanent-magnet linear synchronous motor (PMLSM) to improve its low speed stability and position tracking performance. With this new model, which uses the d-q reference frame, the force ripple information could be calculated at discrete positions using the winding features and magnetic flux density (MFD). A PMLSM with two movers and one stator was designed to measure the air gap MFD and force ripple at different positions. The reliability of the model was validated through a comparison of the force ripple data obtained with the new model and practical measurements. The error ratio between the theoretical calculations and measured forces was less than ± 4%. Force constants were available from the model using the measured MFD, and these force constants were then used as force compensation coefficients to adjust the current in terms of the mover’s position. The force ripple, particularly the periodic force ripple causing resonance of the mechanical system, was significantly reduced with compensation. The theoretical analysis and experimental results show the effectiveness of the improved model.