Feature Investigation of a Segmented Poles Quasi- Halbach T-LSM: Application to Free Piston Engines

The paper is aimed at an investigation of the featuresof a tubular-linear synchronous quasi-Halbach machine (T-LSM)where the radially-magnetized PMs are substituted by four equalsegments with parallel magnetization. This substitution is donein an attempt to improve the machine cost-effectiveness whichmakes it a viable candidate to equip free-piston engine-basedseries hybrid propulsion systems. The study is initiated by ananalytical formulation of the air gap flux density considering (i)the case of the conventional quasi-Halbach T-LSM and (ii) thecase of the segmented pole one. The comparison between thetwo T-LSMs is extended to a 3D finite element analysis (FEA)-based investigation of their no- and on-load features. Followingthe prototyping of the quasi-Halbach T-LSM with segmentedpoles, selected features predicted by 3D FEA are experimentally-validated.It is shown that while the PM segmentation slightlyaffects the machine back-EMF and cogging force, it has aremarkable fallout on its force production capability which makesit necessary the assessment of the cost-performance trade-off.

本论文旨在研究管式直线同步准哈尔巴赫电机（tubular-linear synchronous quasi-Halbach machine，T-LSM）的性能特征，该电机将径向充磁永磁体（permanent magnet，PM）替换为四段平行充磁的均等分段结构。该替换方案旨在提升电机的成本效益，使其成为适配基于自由活塞发动机的串联式混合推进系统的可行候选方案。本研究首先针对两种结构分别推导气隙磁通密度的解析模型：一是传统准哈尔巴赫T-LSM结构，二是磁极分段后的新型结构。随后，研究将两种T-LSM的对比拓展至基于三维有限元分析（finite element analysis，FEA）的空载与负载工况性能研究。在完成磁极分段式准哈尔巴赫T-LSM的样机试制后，研究通过实验验证了三维FEA预测的部分性能特征。研究表明，尽管永磁体分段对电机反电动势与齿槽转矩的影响较为有限，但其对电机出力性能却存在显著影响，因此有必要对其成本与性能的权衡关系进行评估。