IEEE Electrification Magazine - March 2014 - 65

enforced voltage drop, droop coefficient settings and load
variations also have an influence on steady-state voltage,
which may then in total considerably deviate from the
nominal value. For that purpose, a secondary voltage regulator can be deployed in parallel with current flow controller to restore the deviation. naturally, not every bus can be
operated at the nominal value, but the best that can be
done is to restore the average voltage of all buses. therefore, as depicted in Figure 9, two signals will form the outer
voltage reference designated for primary control loop, i.e.,
dv t and dv s .
it can be noted that the secondary control in Figure 9 is
designed in decentralized fashion so that every MG has a
dedicated secondary controllers that are able to exchange
information with its neighbors others using communication infrastructure, which is normally referred to as the
networked control system (ncs). such an ncs may be
realized by means of static averaging calculation or using
dynamic consensus algorithms. Both of the aforementioned variations are active areas of research.
another control layer, referred to as the supervisory
control or energy management system, may be incorporated as well. its functionalities are much more flexible
and normally comprise decision-making mechanisms
that aim to enhance the operational efficiency or to govern the MG through different operational modes. one of
the roles under the jurisdiction of supervisory control is to
determine required current exchanges between different
MGs depending on internal parameters such as socs of
online ess systems and/or energy available from res.

Conclusion
today, the world has to deal with a scenario where various
electronic loads have started to dominate the overall consumption profile. heVs are emerging as a worthy opponent to conventional vehicles, and there is no end in sight
for the rising share of ress in total electricity production.
since dc electricity is an integral part of a large portion of
these modern technologies, there is a need for a reevaluation of the electrical distribution paradigm that was
thought to be resolved in favor of ac at the turn of 20th
century. in that sense, the introduction of dedicated lowvoltage dc electrical distribution systems that are able to
bring the new technologies together and interface them
with ac utility in a more efficient and reliable manner is
gradually becoming a reality.
this article examined the electrical distributions of several modern dc-based industrial appliances and outlined the
need for the modification of existing dc architectures to
enhance their controllability and flexibility. a roadmap for
this shift was proposed through the application of dc MG
technology, where several control levels have been examined. in line with that, a layout of a multibus dc MG with an
associated hierarchical control structure that is able to regulate the current flows between different buses with respect
to nominal voltage levels has been presented.

For Further Reading
P. Fairley. (2013, May 21). edison's revenge: the rise of dc
power. MIT Technol. Rev. [online]. available: http://www.
technologyreview.com/news/427504/edisons-revenge-therise-of-dc-power/
M. liserre, t. sauter, and J. Y. hung, "Future energy systems: integrating renewable energy sources into the smart
power grid through industrial electronics," IEEE Ind. Electron. Mag., vol. 4, no. 1, pp. 18-37, Mar. 2010.
s. Massoud amin and B. F. wollenberg, "toward a smart
grid: Power delivery for the 21st century," IEEE Power Energy Mag., vol. 3, no. 5, pp. 34-41, 2005.
h. Farhangi, "the path of the smart grid," IEEE Power
Energy Mag., vol. 8, no. 1, pp. 18-28, 2010.
B. t. Patterson, "dc, come home: dc microgrids and the
birth of the 'enernet'," IEEE Power Energy Mag., vol. 10, no. 6,
pp. 60-69, 2012.
G. allee and w. tschudi, "edison redux: 380 Vdc brings
reliability and efficiency to sustainable data centers," IEEE
Power Energy Mag., vol. 10, no. 6, pp. 50-59, 2012.
d. Boroyevich, i. cvetkovic, d. dong, r. Burgos, F. wang,
and F. lee, "Future electronic power distribution systems a
contemplative view," in 2010 12th Int. Conf. Optimization
of Electrical and Electronic Equipment, 2010, pp. 1369-1380.
r. h. lasseter, "MicroGrids," in 2002 IEEE Power Engineering Society Winter Meeting Conf. Proc. (cat. no.
02ch37309), vol. 1, pp. 305-308.
F. Katiraei, M. r. iravani, and P. w. lehn, "Micro-grid
autonomous operation during and subsequent to islanding process," IEEE Trans. Power Delivery, vol. 20, no. 1,
pp. 248-257, Jan. 2005.
J. M. Guerrero, J. c. Vasquez, J. Matas, l. G. de Vicuna, and
M. castilla, "hierarchical control of droop-controlled ac
and dc microgrids-a general approach toward standardization," IEEE Trans. Ind. Electron., vol. 58, no. 1, pp. 158-172,
Jan. 2011.
h. Kakigano, Y. Miura, and t. ise, "low-voltage bipolartype dc microgrid for super high quality distribution,"
IEEE Trans. Power Electron., vol. 25, no. 12, pp. 3066-3075,
dec. 2010.
t. dragicˇevic´, J. Guerrero, J. Vasquez, and d. skrlec,
"supervisory control of an adaptive-droop regulated dc
microgrid with battery management capability," IEEE
Trans. Power Electronics, vol. 29, no. 2, pp. 695-706, 2014.

Biographies
Tomislav Dragicˇevic´ (tdr@et.aau.dk) is a postdoctoral
researcher at aalborg university, denmark.
Juan C. Vasquez (juq@et.aau.dk) is an assistant professor at aalborg university, denmark.
Josep M. Guerrero (joz@et.aau.dk) is a full professor at
aalborg university, denmark.
Davor Škrlec (davor.skrlec@fer.hr) is a full professor at
the Faculty of electrical engineering and computing, university of Zagreb, croatia.

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