Magnetic circuit analysis and performance improvement of a tubular staggered-tooth transverse-flux linear machine for free-piston energy converter

A free-piston energy converter (FPEC) integrated by a combustion engine and a linear electric machine is suitable for series HEV or other applications stand-alone generators . The transverse-flux machine (TFM) is considered advantageous for such application because of its high specific power and force density. The finite element method (FEM) is widely used in the machine analysis, which is time-consuming . The equivalent magnetic circuit analysis is a time-effective method compared with FEM. In this paper, a tubular staggered-tooth transverse-flux permanent magnet (PM) linear synchronous machine (STTF-PMLSM) is proposed, which is used for FPEC. The machine is characterized by a relative high power factor due to the low flux leakage. An equivalent magnetic circuit model of the machine has been proposed . The magnetic circuit analysis results are validated by the results of 3-D FEM simulation. The influence of leading design parameters, mainly containing PM magnetization length (h_m), pole pitch (p) and length of the stator core (l_s), on the performance of machine is analyzed in detail.