PRODUCT SPOTLIGHT:
DC-DC CONVERTERS
FOR RENEWABLE ENERGY APPLICATIONS


Introduction

AE Series cover image

Welcome to the CUI Product Spotlight on dc-dc converters for renewable energy applications. This resource will provide an overview of the growing renewable and solar energy markets and outline the rise of 1500 Vdc photovoltaic (PV) systems. It will also introduce CUI’s AE series of ultra-wide input dc-dc converters, which are specifically designed to support the higher voltage requirements of 1000 Vdc and 1500 Vdc renewable energy systems.

Objectives

  • Discuss the growing renewable and solar energy markets
  • Outline the rise of 1500 Vdc photovoltaic (PV) systems
  • Detail the challenges for dc-dc converters that can support these higher voltages
  • Highlight CUI’s AE series of ultra-wide input dc-dc converters

The Solar and Renewable Energy Markets

Solar and renewable energy markets

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.

1000 Vdc Photovoltaic Systems

Typical photovoltaic arrangement

Photovoltaic systems have always been limited by the low efficiency of the solar panels themselves, as 25% efficiency would be the market-leading or theoretical maximum level of monocrystalline cells. Therefore, in order to produce as much energy from the system as possible, PV designers must try to minimize losses in connections and the conversion process from panel dc output to ac for the grid. This is done by connecting panels in series, so that power is processed at high voltages where currents and “I2R” losses are lower. For example, grid-connected systems typically have blocks of 22 panels with cells connected in strings to give 1000 Vdc producing 5.5 kW per string. 2727 strings might then be combined for a 15 MW installation. However, the line loss of 1000 Vdc systems can be further reduced if the system could accept higher input voltages, which is where 1500 Vdc systems have come into play.

Cost Savings of 1500 Vdc Photovoltaic Systems

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.

Component Component Count Unit Cost System Cost (per W)
PV Modules Same +1~2% +$0.02
Cables, Conduits, Trenching -40~45% Same -$0.03
Combiner Boxes -33% +10~20% -$0.005
PV Inverters -40% +80~100% +$0.01
Ac Subsystem Reduced -10~15% -$0.005
Direct Labor N/A -$0.03

Auxiliary Circuits in PV Systems

Diagram of a solar combiner unit with a wide input dc-dc converter

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.

Available Products

Summary image

To address these design challenges, CUI has developed a family of off-the-shelf power solutions. The AE series is a range of dc-dc converters specifically designed to support both 1000 Vdc and 1500 Vdc photovoltaic systems thanks to input ranges of 100 to 1000 Vdc or 200 to 1500 Vdc. These ultra-wide input dc-dc converters offer power ratings from 5 to 40 W, while featuring 5600 Vdc isolation, rated operation up to 5000 meters, and an operating temperature range from -40 up to +70°C with no derating. With available outputs of 5, 9, 12, 15, or 24 Vdc, the parts comes as standard with over voltage, over current, and continuous short circuit protections.

  • 5 to 40 W power ratings
  • Fully encapsulated packages
  • Input voltages up to 1500 Vdc
  • Input voltage ranges up to 10:1
  • 5600 Vdc input to output isolation
  • -40 to 70°C operating temperature range
  • Rated operation up to 5000 meters
  • Over voltage, over current, short circuit protections

AE-EW Series Overview

AE-EW Series

CUI’s AE-EW series comes available in board mount, chassis mount, and DIN rail mount configurations with 5, 10, 15, and 40 W power ratings. The series features input to output isolation up to 5600 Vdc, a 100 to 1000 Vdc input voltage range, and rated operation up to 2000 meters. It also carries EN 62109-1 safety approvals and complies with CISPR22/EN55022 Class A limits for conducted and radiated emissions.

Series Power (W) Output Voltage (Vdc) Isolation (Vdc) Input Range (Vdc) Package Type
AE5-EW 5 5 5600 100~1000 Board Mount
AE5-EW-T 5 5 5600 100~1000 Chassis Mount
AE10-EW 10 5, 9, 24 5600 100~1000 Board Mount
AE10-EW-DIN 10 5, 9, 24 5600 100~1000 DIN Rail
AE10-EW-T 10 5, 9, 24 5600 100~1000 Chassis Mount
AE15-EW 15 12, 15, 24 5600 100~1000 Board Mount
AE15-EW-DIN 15 12, 15, 24 5600 100~1000 DIN Rail
AE15-EW-T 15 12, 15, 24 5600 100~1000 Chassis Mount
AE40-EW 40 12, 15, 24 4000 100~1000 Board Mount
AE40-EW-DIN 40 12, 15, 24 4000 100~1000 DIN Rail
AE40-EW-T 40 12, 15, 24 4000 100~1000 Chassis Mount

AE-UW Series Overview

AE-UW Series

Offering 10, 15, and 40 W power ratings, CUI’s AE-UW series is housed in fully encapsulated board mount packages with 5600 Vdc isolation, a 200 to 1500 Vdc input voltage range, and rated operation up to 5000 meters. The AE-UW series carries the same safety approvals as the AE-EW series and is further designed to meet UL 1741.

Series Power (W) Output Voltage (Vdc) Isolation (Vdc) Input Range (Vdc) Package Type
AE10-UW 10 5 5600 200~1500 Board Mount
AE15-UW 15 12, 15, 24 5600 200~1500 Board Mount
AE40-UW 40 12, 15, 24 5600 200~1500 Board Mount

Applications

Applications image

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.


Off Grid

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


Distributed

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


Centralized

  • Large array
  • Rooftop residential


Other

  • Wind turbines

Summary

The global market for renewable energy is continually on the rise, which presents challenges for system designers. As auxiliary power supplies are a significant part of the monitoring and control of these systems, they need special characteristics to withstand higher operating voltages while complying with reliability and safety standards. CUI’s AE series with its ultra-wide input voltages and other key features offers system designers and integrators an off-the-shelf solution for easy implementation into renewable energy applications.

 
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