A novel tubular transverse-flux moving-magnet linear oscillating generator designed for free-piston engines

Linear generator is the most important component of free-piston engine generators, which are considered as ideal range extenders used in electric vehicles. A novel tubular transverse-flux moving-magnet linear oscillating generator (TFLOG) is proposed in this paper for the application of free-piston engines. An equivalent magnetic circuit of the linear generator is established to analyze the main structure parameters, including magnet thicknesses, air gap length, longitudinal tooth spacing, and coil turns, etc. A finite element model is created to simulate the electromagnetic characteristics and optimize the performance of the linear generator. Electromagnetic force, electromotive force, and coil inductance are analyzed by the static solver, while generating power, copper losses, iron losses, and dynamic characteristics are analyzed by the transient solver. The generating efficiency of 91.5% and the power density of 161 W/kg are obtained by the optimized prototype, which are comparable to the reported longitudinal-flux linear generator and can be more easily manufactured with lower costs. Finally, multiobjective optimization was carried out. The inductance has been reduced by 30%, and the power factor has been increased by 20% on the premise of meeting the basic design power requirements.