Dynamic Characteristic Analysis of Electromagnetic Parameters in Linear Alternators Based on the Circuit Resonance Method

The free-piston Stirling generator (FPSG) is a thermo-mechanical–electrical energy conversion system in which the linear alternator converts reciprocating mechanical power into electrical power. Reliable system-level power calculations require an electromechanical conversion coefficient that represents the alternator under the relevant operating condition. This study evaluates a circuit-resonance-based procedure for identifying the operating inductance and electromotive force (EMF) constant from measured voltage and current amplitudes and phases. Static and dynamic tests were conducted on one laboratory-scale alternator driven by opposed compressors. The dynamically identified EMF constant was compared with the equilibrium-position and stroke-equivalent static force constants in the same Sage model. At 60 Hz with a 4 Ω load and a 272 μF series capacitor, the run using the dynamic parameter gave a mean absolute error of 159.07 W, a root mean square error of 231.72 W, and a mean absolute percentage error of 2.60% over 1876 experimental points; the corresponding mean absolute percentage errors for the two static inputs were 45.94% and 43.67%. These results quantify agreement for the tested alternator and operating condition. Further measurements at other frequencies, loads, and machines are needed to establish broader applicability.