Direct current (DC) and alternating current (AC) technologies have been evolving since Tesla and Edison competed in the late 19th century to establish a distribution method for the electrical grid. At that time, technologies were not available to safely and economically use DC over long distances, so AC was imposed on the grid. Today, using DC over long distances is cost-effective, DC-based renewable energy is proliferating, and most technological equipment operates on DC. However, the electrical grid continues to distribute AC, creating increasing inefficiencies in this energy-hungry, technology-driven world.
“Recent advances in power conversion technologies, combined with the rapid increase in DC-based equipment, have created an environment where 400V DC power distribution must be (and is) actively considered,” says Mark Murrill, director of 400V DC power initiatives at Emerson Network Power. He added: “The global architectural standards needed for widespread application of 400 VDC power are progressing well, as demonstrated by the European Telecommunications Standards Institute (ETSI) standard EN 300 132-3-1 published in February 2012. As suppliers implement this standard, the adoption of 400 VDC power will begin to increase rapidly in various applications, and new standards will be defined and adopted.”
Emerson Network Power currently envisions four main applications for the use of 400 VDC technology: telecommunications headquarters, data centers, commercial buildings, and transportation. Each of these presents key factors for its implementation
Telecommunications: Reducing Copper (and Costs) in the Central Office.
Unlike the electrical grid, telecommunications networks have long used DC power distribution, largely due to its high reliability and good signal quality performance. As silicon-based DC technology has been adopted in telecommunications equipment, there is already an alignment between existing DC power distribution and DC-using equipment, although there is still room for improvement in terms of cost and efficiency. For example, 400 VDC power is particularly well-suited to long-distance, power-intensive applications, as it reduces installation and operating costs and improves cable management compared to -48 VDC power. These benefits are achieved by reducing the amount of copper cabling used by at least 80%, which impacts both cost and installation time. Furthermore, the reduction in line losses will generally also increase end-to-end energy efficiency, further reducing operating costs.
Data Centers: Reducing Conversion Losses.
The rationale behind using 400 VDC power in a data center is based on the need for high availability, high efficiency, and reduced total cost of ownership. Since AC power must ultimately be converted to DC power for use by all IT equipment, and because stored-energy systems (batteries, flywheels, etc.) and renewable energy sources provide DC power, they require a typical DC power architecture with fewer power conversions from the grid to the chip. Reducing these conversions not only saves energy but can also increase the availability of critical power through simplified distribution and fewer points of failure in the power supply chain. Furthermore, DC power does not require phase balancing or harmonic considerations, thus eliminating stagnation due to reduced power output to the equipment.
Other DC power options for data centers include those based on -48 VDC, which are ideal for row-based solutions where loads are very close to the UPS. This -48 V topology cannot be compared to a traditional room-based AC UPS system, but now, with the introduction of 400 VDC power components and systems, the advantages of DC power are available for the first time in an enterprise-class data center power solution.
“Telecom head offices are increasingly resembling traditional data centers. As they adopt higher power densities and more IT equipment in their headquarters and cable headends, the distinction between data center operations and telecom offices is blurring,” says Rhonda Ascierto, principal analyst at 451 Research. “The extent to which companies can take advantage of the savings from DC power varies from data center to data center. However, at least in theory, the benefits of using DC power in data centers seem obvious: servers use DC power, and the fewer the AC power conversion steps from the grid to the servers, the greater the efficiency,” Ascierto explains.
Commercial Buildings: Renewable Energy Drives the Shift and Enhances Advantages. Whether motivated by economic or civic reasons, building owners and managers are increasingly using smart solutions that reduce energy consumption by harnessing renewable energy sources and materials. Using on-site renewable energy generation can reduce or even eliminate the demand for electricity from the grid. This is particularly significant for 400V DC power, as renewable energy sources generate DC current. This means that using this energy for AC applications within the building requires multiple DC-to-AC conversions, thus reducing the efficiency of renewable energy generation. To avoid these additional conversions, architects and engineers are designing buildings with 400V DC "microgrid" power distribution systems, either globally or in specific areas of buildings or campuses. This solution increases the system's energy efficiency, simplifies the microgrid, and improves reliability while reducing operating costs. Furthermore, when a building or campus microgrid is powered by multiple energy sources, 400 VDC power distribution is easier to manage because, unlike AC, DC sources do not require synchronization. This means the primary power source can be selected in real time based on factors such as availability (of solar or wind power, for example) and cost (electricity tariffs).
Transportation: DC distribution is already in use and its advantages will become widespread.
Transportation vehicles of many types (cars, ships, public transport, trains, construction machinery, etc.) are integrating DC power for motor drive and other loads to increase efficiency and save fuel. For example, in the maritime and rail transport sectors, DC power is increasingly being used for propulsion and integrated loads. Similarly, as electric and hybrid vehicles such as cars and buses become more common, DC power will be the logical choice for fast charging and operation in vehicle systems. In these and other types of vehicles, direct current will be used with current and 400V distribution technologies as they continue to evolve towards hybrid and fully electric systems.
Emerson is a member of EMerge Alliance, an open industry association that develops standards for the widespread adoption of DC power distribution in commercial buildings.
