Cogging Force Reduction in PMLSMs Using Segmented Magnets

Abstract

Permanent Magnet Linear Synchronous Motors (PMLSMs) suffer from inevitable cogging force, especially in low-speed applications. In this paper, a new PMLSM is presented that uses segmented magnets instead of typically used rectangular magnets. This results in a significant reduction in cogging force and improved back EMF waveform. However, with these types of magnets, the actual three-dimensional (3D) structure of the machine cannot be reduced to a 2D problem because the thickness of the magnets varies with the depth of the device. Although 3D Finite Element Analysis (FEA) can be used, this method is very time-consuming even for one calculation step, which makes it difficult to use in optimization processes. To overcome these challenges, quasi-3D approach is used to transform the actual 3D structure of the machine into several 2D models and find the overall performance by combining the results obtained for each 2D problem. Genetic algorithm combined with quasi-3D method is used to find the appropriate thickness of each PM segment.