IEEE Electrification Magazine - June 2016 - 21

In line with the developments previously mentioned, direct-current
(dc) distribution systems are making their way back to electrical grids.
Worldwide, today's electrical systems predominantly use alternating
current (ac); however, the technical/technological problems that, over a
century ago, made dc harder to transmit than ac have been solved.
Both ends of the electrical spectrum, high voltage (HV) and LV, have
seen the proliferation of dc systems and its implementation for transmission and distribution of electricity. For both ends, dc offers significant improvement regarding simplicity, efficiency, and cost reduction.
DC systems are now viable options as a result of developments that
have taken place in the power electronics industry, which have allowed
converters to operate at dc voltage levels required for transmission, distribution, and consumption.
Starting from the top end, there are over 100 HV dc (HVdc) systems
already installed around the world, especially for long-distance and submarine connections. HVdc transmission systems allow higher efficiency,
potentially lower costs, and enhanced environmental solutions. HVdc
transmission lines are generally thinner than HVac lines for the same
power capacity; also, HVdc allows long-distance transmission with underground lines, thereby considerably reducing the environmental impact.
Moving to the bottom end, dc provides a promising solution for modern
power systems to improve efficiency, power quality, resiliency, and reliability. Despite having no presence in grid applications, these benefits have
been previously observed in several stand-alone applications, such as
vehicular power systems, telecommunications stations, data centers, and
aerospace, marine, and other electrical power systems in which reliability,
efficiency, and cost are critical.

Potential Benefits of LVdc Distribution
Systems for Building Applications
The high penetration of installations with DGs at consumption level,
especially solar photovoltaic (PV) panels, ESSs, and modern electronic
loads, gives dc distribution a competitive advantage when compared
with ac for residential/building applications. Most renewable energy
generators, such as PV panels and fuel cells (FCs), are dc generators;
however, even WTs, intrinsically ac generators, are more conveniently
integrated into a dc grid since double conversions are avoided. ESSs as
batteries are dc devices as well. Furthermore, modern electronics loads
[e.g., TVs, light-emitting diode (LED) lights, phones, computers] are all
internally dc loads, and the energy consumed by these devices is
increasing every day. Moreover, as has happened with WTs, even appliances that are intrinsically ac loads (e.g., refrigerators, washing
machines, dishwashers) interface better with a dc supply, because of the
elimination of ac-dc conversion. In addition, the expected future integration of electric vehicles (EVs) is going to inevitably increase the presence of dc devices in buildings' electrical systems because, basically, EVs
have batteries that can be charged or discharged. Therefore, a dc distribution system is a more natural interface between mostly dc devices,
which allows considerable power-conversion stage reduction, hence
achieving a significant loss reduction, as well as simplicity and potential
cost reduction in the power converter units.
On top of this, there are a few common benefits of dc when compared
with ac for all applications. For example, in dc there is no reactive power
loading the lines, and there is no need for synchronization. As a consequence, the system naturally becomes more efficient and simpler. It is
important to highlight that dc efficiency or energy-saving improvement
IEEE Electrific ation Magazine / j une 2 0 1 6

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

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