IEEE Electrification Magazine - June 2016 - 22

is strongly related to the presence of local RESs and
ESSs. When examining the LVdc distribution system in
Figure 1, if there is low or nonlocal generation and no
storage, most of the energy consumed by the load would
inevitably come from the grid rectifier. The grid rectifier
would be sized to supply the approximate building-installed power;
however, the loads are normally connected at different times. Hence, it is
expected that the rectifier works
mostly at low loads where its efficiency is very poor, thereby increasing system losses considerably.

converters, protection devices, connectors, chargers)
that comply with the system's requirements, especially
regarding the voltage level. Also, consumers would find
it extremely difficult to find dc-compatible appliances
and devices.
As for standards, several organizations such as EMerge Alliance, the
European Telecommunications Standard Institute (ETSI), the International
Electrotechnical Commission (IEC),
the IEEE, and others, are working to
develop the required regulation for
the implementation of dc systems for
building/residential applications.
According to the IEC 60038 standard,
LVdc systems are defined as those
with voltage levels below 1,500 V. This
range gathers several applications,
from computer electronics to automotive, marine, and aerospace power
systems. Figure 2 shows an overview
of the voltages and standards used in
the different applications.
Protection devices, fuses, and circuit breakers (CBs) can sometimes be
used directly in dc systems, but these
devices are currently designed for ac
systems. The current-interruption mechanisms rely mainly on the natural zero crossing of the ac current, with
development of arc voltage being a secondary effect for CB
clearing., In dc systems, because the fault current does not

Worldwide, today's
electrical systems
predominantly use
ac; however, the
technical/
technological
problems that, over
a century ago, made
dc harder to
transmit than ac
have been solved.

Challenges and
Safety Concerns

As mentioned, LVdc distribution
systems for residential/building
applications have brought high
expectations regarding simplicity,
cost reduction, reliability improvement, and energy savings. The lack
of commercially available products,
standards, codes, and regulations
for dc systems is a critical challenge
holding back a wider implementation of LVdc distribution systems.
Such a lack of commercially available products is an
issue for companies implementing dc systems and system users. When designing LVdc electrical power systems, it would not be easy to find products (e.g., power

Battery

EVs

PV Panels

PV Panels
dc
dc

ac
ac

dc
dc

dc
ac

Grid

Battery

dc dc

dc
dc dc

Appliance Electronics

ac Voltage
Distribution
Line

Lighting
System

dc Voltage
Distribution
Line

Figure 1. A reduction in power-conversion stages enabled by dc.

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

η(%)

P (W )
Grid Rectifier
Efficiency

Energy Path When Loads
Are Fed from the RES
Production Stored in the ESS

Appliance Electronics Lighting
System
Energy Path When Loads
Are Fed from the Grid

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