A free-piston engine linear generator system is expected to be used as a high-efficiency energy conversion device for a series hybrid electric vehicle. The piston action can be controlled using generation control because this system has no crank mechanism. The copper loss is reduced by using output dispersion between the expansion and compression stroke for a longer stroke. We built a power generation experiment device that simulates combustion and power generation with two motors. By increasing the stroke after the scavenging point, the output power between the expansion stroke and the compression stroke was dispersed, and the copper loss was reduced by 23%.