A new family of a single-switch three-diode dc-dc pulsewidth-modulated (PWM) converters operating at constant frequency and constant duty cycle is presented in this paper. The proposed converters are different from the conventional dc-dc step-up converters, and they posses higher voltage gain with small output voltage ripples. Other advantages of the proposed converters include lower voltage stress on the semiconductor devices, simple structure, and control. Moreover, the reduced voltage stress on the diodes allows using Schottky diodes for alleviating the reverse-recovery current problem, as well as decreasing the switching and conduction losses. The principle of operation, theoretical analysis, and experimental results of one prototype rated 40 W and operating at 94 kHz are provided in this paper to verify the performance of this new family of converters.

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In this paper, a new single-switch nonisolated dc-dc converter with high voltage transfer gain and reduced semiconductor voltage stress is proposed. The proposed topology utilizes a hybrid switched-capacitor technique for providing a high voltage gain without an extreme switch duty cycle and yet enabling the use of a lower voltage and R DS−ON MOSFET switch so as to reduce cost, switch conduction, and turn-on losses. In addition, the low voltage stress across the diodes allows the use of Schottky rectifiers for alleviating the reverse-recovery current problem, leading to a further reduction in the switching, and conduction losses. The principle of operation and a comparison with other high step-up topologies are presented. Two extensions of the proposed converter are also introduced and discussed. Simulation and experimental results are also presented to demonstrate the effectiveness of the proposed scheme.Index Terms-DC-DC power conversion, high step-up converter, pulsewidth modulated, switched-mode power supplies.

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a b s t r a c tPeople's extensive and ignorant lifestyles impose an increasing amount of destruction on the environment, which lead to an increased governmental and research interest towards the development and use of green technology such as fuel cells. Fuel cells are recently receiving a major share of research interest due to their promising features. This paper presents an offline parameter identification approach based on particle swarm optimization (PSO) to identify the mathematical modeling parameters of the Nexa 1.2 kW proton exchange membrane fuel cell (PEMFC) system. The goal of this work is not to get a new technique in modeling, but rather to obtain a very good model of the PEMFC system using a simple and fast heuristic approach that requires minimal mathematical effort. This model can then be utilized to perform further analysis and fault diagnosis studies on PEMFCs. The proposed approach uses basic fitting to determine some of the initial values for the PSO, while the rest of the initial values are set to be chosen randomly. The developed model is then successfully validated using actual experimental data sets.