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Auxiliary
The combiners and inverters in a PV system need low voltage isolated power for monitoring and control derived from the 1500 VDC line, but finding small DC-DC converters that operate at these levels is not easy. The lower voltage end could also dip under 200 VDC under particular conditions, meaning the converter needs to provide at least a 7.5:1 input range to support these wide fluctuating voltages. This wide input range is difficult to achieve with standard flyback or forward converter topologies, especially with high maximum input voltages. The variation in pulse width to regulate the output, internal peak voltages and extreme currents, further necessitates a more complex topology. Operating under different illumination conditions means the DC-DC converters require protection from frequent “brown-outs” as the input drops below the minimum threshold, while also needing to deal with over current, over voltage, and short circuit fault conditions typically seen in remote applications. As PV systems also require direct sunlight, temperatures in control cabinets can rise dramatically, making the operating temperature range of the DC-DC converter another key consideration. All of these challenges combine to make the selection of a DC-DC converter for PV applications no simple task.
PTM Published on: 2018-09-13