Design and optimization of a single-phase oscillating PM alternator used for free-piston stirling engines

A single-phase oscillating permanent-magnet (PM) alternator is proposed for free-piston stirling engines. According to its sinusoidal kinetic characteristic, the design principle of this machine is proposed. On this basis, the finite-element model is built. Since the no-load back EMF and no-load thrust are two key indexes for the single-phase oscillating PM machine, the influence of PM thickness on the no-load back EMF and no-load thrust is further investigated. Then an optimal scheme of single-phase oscillating PM machine is obtain. Because this machine has two working modes, the electromagnetic performance of two working modes is analyzed. In the generator mode, no-load and load back EMF, voltage harmonics distortion ratio, the voltage regulation ratio and kinetic characteristics are deeply analyzed. Then in the motor mode, the electromagnetic force versus current is investigated. That proves the electromagnetic thrust per current can reach 35.7 N/A.