Performance Measurements and Control Characteristics of a 1 kW Class Free Piston Stirling Converter With AC Bus Controls

An experimental study of the control characteristics of a 1 kW class free-piston stirling converter (FPSC) with alternating current (AC) bus controls is conducted. A performance test rig is constructed using a commercial beta-type FPSC, and an AC bus controller that includes a tuning capacitor, a set of load resistors, and an AC power supply is developed. Experiment parameters include the tuning capacitance and load resistance for the AC bus circuit and the control voltage and control frequency for AC bus control under various head temperatures of the test FPSC. In addition, preliminary experiments under load resistance control scheme were conducted to identify the natural operational characteristics of the test FPSC without an external active control scheme and to determine the proper ranges of the experiment parameters for AC bus control. The experimental results are presented in terms of the output power, the power factor, and the thermal-to-electric efficiency of the FPSC with respect to the load resistance and the AC bus control parameters. In particular, the effect of the control frequency with respect to the FPSC operating frequency, as well as the influence of the alternator inductance on the control characteristics of FPSC are discussed in detail. Finally, it is anticipated that this research will yield a better physical understanding of comprehensive AC bus parameters related to the performance of FPSCs, will provide a simple and accurate control method for laboratory experiments on FPSCs, and will provide fundamental data for those who design advanced virtual tuning capacitor controllers.