| Summary: | 碩士 === 元智大學 === 電機工程學系 === 93 === This thesis presents two kinds of newly designed dc-dc converters for a fuel cell generation system in order to satisfy high-voltage demands. Because the fuel cell has the power characteristic of low voltage and high current due to the electrochemical reaction, a high step-up dc-dc converter is devised for boosting the fuel-cell voltage up to a constant dc-bus voltage. A high-efficiency voltage-clamped dc-dc converter is proposed in this thesis to design by way of the combination of inductor and transformer to increase the voltage gain. Moreover, one additional inductor provides the reverse current path of the transformer to enhance the utilization of magnetic core. In addition, the voltage-clamped technology is used to reduce the switch voltage stress so that it can select the Schottky diode in the output terminal for alleviating the reverse-recovery current and decreasing the switching and conduction losses. Thus, the proposed converter topology has favorable voltage-clamped effect and superior conversion efficiency.
On the other hand, a battery-based energy storage system is required owing to the fuel cell without energy storage capability. Employing batteries in power system can provide the power requirement for fuel-cell start-up and peripheral instruments, and reduce the corresponding installed capacity to further save the cost of system purchasing and power supply. Therefore, multi-input bidirectional power converters are essential to enable multiple-source technology. In this thesis, it takes a three-winding coupled inductor as the main component of energy transmission, and utilizes only two power semiconductor switches to accomplish the multi-input mechanism according to the electric characteristics of fuel cell. Moreover, the requirement of battery charge power can be acquired directly from fuel cell through the coupled inductor so that it avoids the power losses induced by the multistage conversion in the traditional auxiliary power systems, and manipulates the synchronous rectification technique to further decrease the conduction losses. In addition, the devices with low conduction losses can be adopted in the low-voltage side with high current, and there is no high voltage spikes and stresses in the high-voltage side with low current. Finally, some experimental results via an example of a proton exchange membrane fuel cell (PEMFC) power source with 250 watts nominal rating are given to demonstrate the effectiveness of the proposed power conversion strategies.
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