Multi-domain physical modeling and dynamic performance analysis of a free-piston Stirling generator

Free-piston Stirling generators (FPSGs) are regarded as a promising energy conversion technology for their reliable and highly efficient operation. Given the complexity of the coupled dynamic and thermodynamic processes, an accurate and fast dynamic model is crucial for the design and analysis of FPSGs. In this study, a time-domain physical model of an FPSG is developed using MATLAB Simulink® and its Simscape™ software package. Model validation shows that the average deviations between the simulation results and experimental data in steady state are 2.5 % for electric power and 13.4 % for thermal-to-electric efficiency. Then, the dynamic performance of the FPSG is investigated, including the piston offset, operating characteristics with and without clearance seals, onset processes for cold and hot start-ups, and dynamic response to load change. Furthermore, the FPSG is connected to a controller employing a hysteresis current control strategy, and the relevant transient behavior is analyzed. The power piston stroke of the FPSG can be maintained at the desired value, and a unit power factor is achieved without the need for the tuning capacitor. The proposed multi-domain modeling and dynamic analysis approach demonstrates sufficient accuracy and versatility, as well as ease of use for guiding experiments and controller design for FPSGs.