Electromagnetic Design and Control Strategy of an Axially Magnetized Permanent-Magnet Linear Alternator for Free-Piston Stirling Engines

A 1-kW axially magnetized permanent-magnet linear alternator and the control strategy are investigated for free-piston Stirling engines (FPSEs). To meet the requirement of FPSE applications, the power densities of axially magnetized and radially magnetized structures are compared, and the shape of the stator end tooth is studied to reduce thrust fluctuation. Moreover, the thermal field of the proposed alternator is investigated for the appropriate selection of insulation class. The equivalent method is used to simplify the thermal modeling of slot coils. Due to the complex control of the FPSE, the stroke control strategy is investigated. Energy storage devices are employed to provide transient power supply and reduce voltage ripple. The hardware structure and voltage control scheme are discussed and validated by Matlab/Simulink. The prototype alternator and controller were designed and tested, and satisfactory experimental results were obtained.