Velocity-Based Control of Piston Trajectory in a Free-Piston Linear Electric Generator by Load Current Modulation

A free-piston engine (FPE) is a type of linearly reciprocating internal combustion engine (ICE) that has several advantages over typical crank-slider engines. When combined with a linear electric generator, the resultant system is a free-piston linear electric generator (FPLG), which may be used for vehicle propulsion and portable power generation. However, displacement endpoints of the piston-permanent magnet assembly are intrinsically unstable even with fixed electrical load, due to fluctuating combustion pressures. Engine stoppage can be caused by low combustion pressures and misfires, due to absence of mechanical flywheel. This work aims to achieve operational stability by controlling electrical load current and targeting a piston trajectory in each cycle. The present paper discusses results of simulation of the FPLG on Matlab-Simulink. Findings shed light on the effects of combustion fluctuation and control of the load current on system operation. By controlling the electrical current drain based on displacement and velocity, continuous steady-state operation can thus be achieved. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.