NOVELTY - A high-efficiency fuel cell power conditioning mechanism has a high-order resonant framework as well as closed-loop control. A fuel cell is operated under an electrochemical principle for converting chemical energy directly into electrical energy. This process produces higher conversion efficiency than conventional thermal-mechanical system because the system has the salient features of quiet operations without pollution. In order to reduce the overall operating cost of a fuel cell system and to satisfy the utility AC power demand, the mechanism investigates a high-efficiency fuel cell power conditioning mechanism with a simple framework. In general, the methodology for inverting DC voltage into low-frequency AC voltage is usually generated by the pulse-width-modulation (PWM) technique. However, the PWM-type inverter output has high-frequency harmonic components, electro-magnetic-interference (EMI) and high-frequency switching loss. Firstly, a boost converter is utilized to raise the DC voltage in the fuel cell output for overcoming the voltage variation problem of the fuel cell with respect to load change. Moreover, a novel power inverter via the LLCC resonant technique is designed for inverting DC voltage into 60 Hz AC sinwave voltage with low harmonic components in this power conditioning mechanism. This circuit scheme has the properties of soft-switching property, high power conversion efficiency and simplified implementation, and no EMI problem. However, the voltage gain of this LLCC resonant inverter is varied according to the nonlinear factors of the switching frequency drift, the load effect, the variation of fuel cell output voltage, and the resonant component parameter perturbation due to heat and magnetic saturation. Therefore, this invention further introduces a closed-loop control scheme to increase the system sensitivity and bandwidth for alleviating the effect induced by nonlinear factors. The novel power conditioning mechanism developed in this invention will be to rise the utility rate for energy, reduce the pollution of the environment, and increase the stability of power supply. It also can be utilized for other power generating types with the necessary of DC/AC power conversion.