DC development for data center power

Back in the 1880s Nikola Tesla and Thomas Edison engaged in the “War of the Currents,” fighting for supremacy between alternating current (AC) and direct current (DC).  The AC solution won and for the past 100 years transmission and distribution architectures throughout the world have been based on AC power.

Some might say that the War of the Currents outcome changed in the 21st century when in May 2012, ABB announced the opening of a 380-volt DC-powered data center at the Green Datacenter Zurich West as first proof of a pioneering direct current concept. The Zurich West data center was selected as ABB’s demonstration site for its new DC technology, which is now recognized as a new option and viable alternative to AC.


Traditional data center designs using AC UPS technology will often use double conversion UPS running in economy “eco” mode to achieve higher operating efficiency.  In this mode the AC UPS is essentially bypassing the AC-to-DC and DC-to-AC rectifiers to reduce the switching losses. 

But there are still several parasitic loads inherent in these systems.  In addition, few designs these days call for more than a 70 – 80% load on a Tier 1 to 3 system and as little as 30 – 40% load on a Tier 4 system UPS.  These are generally in the less efficient range for most AC UPS systems and thus running in eco-mode helps improve the overall efficiency by minimizing the amount of time it is running in double conversion mode.  Most data center operators recognize and willingly accept that a double conversion UPS is only most efficient in eco-mode and less so in double conversion mode.

But these systems are typically “transformerless” and will include several pieces of additional electrical distribution equipment, paralleled UPS modules and cabling to provide a power system that achieves a reliability level the operator is willing to accept, such as N+1 or three nines (99.9%) or more of uptime.  But then this UPS output must go to a PDU (power distribution unit) which then includes a transformer to reduce the voltage to within the server’s acceptable input range.

A DC power system by contrast will have one AC-to-DC conversion and then immediately distribute that DC power out to the server racks via a DC-PDU requiring fewer pieces of electrical switchgear, cable and parallel modules.  With a scalable design the end user can still achieve their reliability and uptime targets but with less overall equipment.

Fewer conversion points means fewer hot spots, power losses, and system vulnerabilities— resulting in greater system stability and a more reliable network with a reduced risk of network outages and a faster recovery time.

The need for fewer components decreases equipment, installation and maintenance costs, reduces the footprint vs. than their AC counterparts, and thus helps optimizing server space and capacity.

While 48VDC systems have been successfully used in telecom facilities for decades, these systems do not scale well in the large hyper-scale data centers of today and occupy valuable whitespace in data centers.  A better means of DC power distribution is now gaining acceptance and adoption in data centers. Through pilot projects, extensive research and development efforts, and collaboration with other thought leaders in the industry ABB continues to develop a 380-volt DC-based power distribution architecture to offer in addition to its broad scope of AC products and systems



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