IEEE Electrification Magazine - June 2016 - 36

devices could scale back or power down less critical features; related to this, the current draft of the update to
the Ethernet standard has such a feature, a local price
index, showing the practicality of the LPD approach. This
example of powering devices needed for reliable communication is another example of how dc distribution can be
introduced for specific needs to gain multiple benefits. In
cases such as these, dc distribution for communications
devices could be initially a dc island but later connected
to other dc domains, including local generation, for greater efficiency and reliability.

Challenges and Opportunities
The key near-term challenge is to do the research necessary
to determine the communications needed between grid controllers and end-use devices and, secondly, between grid controllers. Once this is done, the features required can be added
to all physical layers that implement managed dc. Managed
dc link technologies above 100 W are needed; one implementation of that is from Voltserver, Inc., which offers technology
for managed dc over 1 kW, over relatively thin cable by using
much higher voltages while maintaining safety. The economics of daisy-chaining devices on a power cable are significant,
and developing ways to accomplish this in the context of
LPD will be valuable. LPD is based on a model of peer-to-peer
power exchange. It may be possible in some contexts (perhaps for higher power levels) to create managed dc power
buses, with many devices able to put power on or take power
off at the same time. The electrical engineering and communications aspects of this may be substantial but could offer
compelling efficiency and other benefits. A final challenge
will be to ensure that sufficient end-use devices are available
that implement LPD. The electronics industry shows that
quick innovation and product introduction are possible
when manufacturers see a viable market.

Summary
DC power, particularly with direct dc, has the potential to
save energy, and offers many other benefits. Making this
a reality requires developing new technology. Existing
managed dc creates the possibility for new mechanisms
to choose how to manage generation, storage, and end
use, but because it is limited to a single power links, it has
great limits in how it can be leveraged. Only networked
dc greatly expands the degree of capability and utility of
dc over ac, and LPD is a simple and powerful way to create this. Although direct dc will sometimes be introduced
into buildings in single large installations, more commonly it may be added in small pieces over time, building
an evolving network of power entities inside buildings.

For Further Reading
B. Nordman, "Local Grid Definitions," prepared for the Hometo-Grid Domain Expert Working Group (H2G DEWG), Smart
Grid Interoperability Panel (SGIP), Jan. 5, 2016.

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2016

B. Nordman, K. Christensen, and A. Meier, "Think globally,
distribute power locally: The promise of nanogrids," IEEE Computer, vol. 45, no. 9, pp. 89-91, Sept. 2012.
B. Nordman and K. Christensen, "DC local power distribution with microgrids and nanogrids," in Proc. 1st Int. Conf. DC
Microgrids, Atlanta, GA, 2015, pp. 199-204.
B. Nordman and K. Christensen, "The need for communications to enable DC power to be successful," in Proc. 1st Int.
Conf. DC Microgrids, Atlanta, GA, 2015, pp. 108-112.
USB Implementers Forum. (2012, July 5). Universal Serial
Bus: Power Delivery Specification, Revision 1.0. [Online]. Available: http://www.usb.org/developers/docs/
K. Garbesi, V. Vossos, A. Sanstad, and G. Burch, "Optimizing
energy savings from direct-DC in US residential buildings,"
Lawrence Berkeley Nat. Laboratory, Berkeley, CA, Rep. LBNL5193E, 2011.
LAN/MAN Standards Committee. (2009, Oct. 2). IEEE Std.
802.3at-2009, DTE Power Enhancements. [Online]. Available:
http://www.ieee802.org/3/at/

Biographies
Bruce Nordman (BNordman@LBL.gov) received his B.A.
degree in architecture and his M.A. degree in energy
and resources from the University of California, Berkeley, in 1984 and 1990, respectively. He is a research scientist in the Buildings Technology Department at
Lawrence Berkeley National Laboratory. His research
interests include energy use and efficiency of electronics and networks, low-power-mode energy use, user
interfaces, energy policy, and power distribution technology. He has contributed to many technology standards organizations including the IEEE, the International
Electrotechnical Commission, Ecma International, the
Consumer Technology Association, the Internet Engineering Task Force, and Energy Star specifications and
test procedures.
Ken Christensen (christen@cse.usf.edu) received his
electrical and computer engineering B.S. degree from
the University of Florida, Gainesville, in 1981 and his
M.S. and Ph.D. degrees from North Carolina State University, Raleigh, in 1983 and 1991, respectively. He is a
professor and associate chair of the Department of
Computer Science and Engineering at the University of
South Florida, Tampa. His research interest is in performance evaluation of computer networks. In the past 10
years, he has made significant contributions toward
proxying for network connectivity and energy efficient
Ethernet. This research has contributed to Ecma International, IEEE standards, and Energy Star specifications.
From 1983 to 1995, he was employed at IBM Research
Triangle Park in Durham, North Carolina, as an advisory engineer. He has written more than 100 journal and
conference publications and holds 13 U.S. patents. He is
a licensed professional engineer in the state of Florida, a
member of the ACM and the ASEE, and a Senior Member of the IEEE.

http://www.usb.org/developers/docs/ http://www.ieee802.org/3/at/

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2016