Electrical Load Matching and Loss Mechanisms of a Gas-Coupled High-Power Linear Alternator for Free-Piston Stirling Generators

High-power linear alternators (HPLAs) are key energy conversion components in free-piston Stirling generators (FPSGs), yet their output performance strongly depends on the coupled matching among the gas pressure wave, piston dynamics, and external electrical load. In this work, the electrical load-matching characteristics and loss mechanisms of a gas-coupled HPLA were investigated experimentally and numerically. A thermodynamic–dynamic–electromagnetic coupling model, validated against gas-coupled dynamic experiments, is established to account for the position-dependent electromagnetic parameters and the coupled gas mechanical–electrical interaction. The results show that load resistance mainly governs the current level and the loss composition, whereas series capacitance shifts the electrical phase and modifies the effective electromagnetic stiffness and damping acting on the piston. Consequently, the maximum power condition does not coincide with complete electrical resonance: allowing the capacitance to deviate from resonance raises the maximum output power from 13.54 kW to 14.58 kW, a gain of about 7.7%. Moreover, as the load resistance increases, the dominant loss migrates from current-dependent electromagnetic loss to mechanical damping loss, so that the maximum power point and the maximum efficiency point are clearly separated. These findings establish a coupled load-matching framework for selecting the operating point and external load according to design priority, rather than by electrical resonance alone.