A free-piston PM linear generator in vernier topology using quasi-Halbach-excitation

This paper deals with the investigation of a linear generator used in an internal combustion engine. The introduction reviews the state of the art of free-piston linear generators. Then, the mechanical structure of this generator is presented. The main part treats a finite-element-analysis (FEA) of the generator comparing different armature magnetizations with the numeric simulation program FLUX. A cylindrical design with radial, axial and a quasi-Halbach magnetization in Vernier topology is examined. The number of pole-pairs in a Vernier machine differs by one from stator teeth in principle. This paper is focusing on a Vernier machine with five armature pole-pairs coinciding within six stator teeth (Vernier 5/6). Several geometric parameters, like height of the magnets, slot pitch ratio or length of the magnets are varied in order to find the optimal design with regard to a high thrust force and low force ripple. The paper concludes with the determination of losses and electrical efficiency.