PRODUCT SPOTLIGHT:
DC-DC CONVERTERS
FOR RENEWABLE ENERGY APPLICATIONS

Projected growth for photovoltaic power generation systems is strong with installed global capacity increasing from 178 GW in 2014 to an anticipated 540 GW in 2019. This growth is led by Europe with an expected increase to 158 GW in 2019, while countries like China and the US are expecting four-fold and three-fold increases over that same time span, respectively. A November 2016 report by the US Department of Energy (DoE) further revealed that solar energy accounts for the largest portion of employers in the electric power generation sector, with wind energy being the third largest. In the US, solar energy employed 374,000 people or 43% of the sector’s workforce and wind energy an additional 8% between 2015-16, while globally 55 million people were employed by the solar industry in 2014. Overall, these numbers will only continue to rise, leaving tremendous opportunities for system designers and the products needed to support their growing demands.

By increasing panel numbers in strings to deliver 1500 Vdc to the combiners for the same 15 MW of power outlined on the previous slide, current drops to 66.6% of the 1000 Vdc value and resistive cable losses to 44.4% because of the “I²” in I²R, resulting in higher system efficiency and lower cost of installation with smaller cables and connectors. With fewer strings to achieve 15 MW, 31% fewer combiner boxes are needed (94 compared to 137 assuming each box can handle 20 strings in this example). This means that the associated combiner cabling, connector, and maintenance costs are lowered as well. Broken down in the table below, research has analyzed the cost per watt of 1000 Vdc and 1500 Vdc systems in a 10 MW plant to show a potential deployment savings of $400K in 1500 Vdc installations. But while certainly advantageous from a cost perspective, higher string voltages do have some challenges that need to be taken into account.

Auxiliary Circuits in PV Systems

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.

CUI’s AE series with input voltages up to 1500 Vdc, are ideal for a range of renewable energy and photovoltaic system applications, including off grid, distributed, and centralized solar power equipment, wind turbines, and more. Their rated operation up to 5000 meters further allows for the support of remote, high altitude installations which are common in the renewable energy sector.

• Solar lighting
• Solar pump
• Monitoring for oil, ocean & astronomy
• Solar assisted public transit

• Small size PV plant
• Photovoltaic charging stations
• Building-integrated photovoltaics
• Other utility scale applications

• Large array
• Rooftop residential

• Wind turbines