Research on a tubular yokeless PM linear machine

Free-piston energy converter, which has great potential in applications of space and electric vehicles (EVs), has drawn wide interests in recent years. Free-piston energy converter consists of a free-piston Stiring engine and a linear machine. Tubular permanent-magnet (PM) linear machines are widely adopted due to the salient characteristics like high power density and high efficiency. Radially-magnetized, axially-magnetized, and quasi-Halbach PM linear machines are developed [1-3]. However, the common demerit of the developed machines is the low utilization of space, which provides potential for the improvement of power density. Hence, a novel yokeless PM linear machine is reported in this paper. Compared with conventional PM linear machines, the proposed machine has advantages of higher power density, higher efficiency, and higher utilization of space.