High efficiency and low cost power converters for interfacing energy storage have become critical in renewable energy systems. In this paper a fractional charging converter (FCC) is proposed to reduce power rating as well as cost of the dcdc converter for hydrogen production by alkaline electrolyzer cells. The FCC configuration only processes the partial power resulting from the voltage difference between the source and the energy storage element. Moreover, the converter employed in such configuration can be either isolated or non-isolated, which simplifies topology selection. An analysis and comparison of two dcdc topologies using a high-frequency transformer based on component stress factor (CSF) is performed to determine the optimal solution for the evaluated application. Based on the results of the CSF analysis, and due to its capability of handling wide input voltage, the isolated full-bridge boost (IFBB) converter is designed, built and tested. Experimental results prove the feasibility of the fractional charging configuration with a reduction of 80% of the power rating compared to the traditional interconnection, which implies a reduction in cost, weight and an increase in efficiency. The converter's maximum voltage gain achieved is 25 and the highest measured system efficiency is 98.2 %.

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A review of high voltage gain, high efficiency bidirectional dc-dc topologies is presented. Each converters primary benefit is highlighted, and a summary of all the converters is presented. It is observed that voltage gains higher than 20 is only achieved with topologies using a transformer. The average efficiency of the topologies is slightly lower for isolated topologies. Different strategies are utilized in most of the topologies in order to achieve the high voltage gain, and high efficiency, for example charge pumps, resonant circuits, coupled inductors, and switching cells.

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By a rearrangement of the traditional supply-converter-load system connection, partial-power-processing-based converters can be used to achieve a reduction in size and cost, increase in system efficiency and lower device power rating. The concept is promising for different applications such as photovoltaic arrays, electric vehicles and electrolysis. For photovoltaic applications, it can drive each cell in the array to its maximum power point with a relatively smaller converter; for electric-vehicle applications, both an onboard charger with reduced weight and improved efficiency as well as a fast charger station handling higher power can be considered. By showing different examples of partial-power-processing application for energy-conversion and storage units and systems, this paper discusses key limitations of partial-power-processing and related improvements from different perspectives to show the potential in future power electronic systems.

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A theoretical loss analysis is presented for GaN switches, for which conduction and switching losses are considered, and for planar transformers, where winding and core losses are considered. The analysis is then used to make a comparison of the losses in the partial parallel isolated full bridge boost converter and the isolated full bridge boost converter.

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