IEEE Electrification Magazine - June 2016 - 25

ac Grid

Apartment
Building

Isolated Voltage
Balancer

Apartment
Building

-750 V +750 V
Shopping Center
G

M

M

1,500 V
+375 V

MIcrochip Fans Heat Pumps Lighting
-375 V
PV Plant
Isolated Voltage
Balancer
Heavy Industry
1,500 V

M
Heat
Pumps

House

House

Lighting Converters Process

Figure 4. A schematic of a two-level bipolar LVdc distribution grid.

Voltage Levels for LVdc Distribution
Systems for Building Applications
The voltage-level selection for LVdc distribution systems is
not a straightforward choice, and the discussion on appropriate voltage levels has been going back and forth for
some time. The lack of standardization is palpable when
observing the variety of voltage levels used for LVdc distribution systems in different applications, as shown in Figure 2. The distribution voltages adopted for different
solutions basically depend on what features comprise the
main design criteria. For instance, in the automotive
industry, 12-V distribution systems are used in cars to
guarantee their safety. Nevertheless, the increase in the
number of electronic devices in modern cars leads to
higher electrical consumption. For this reason, 24-48-V
levels have been considered as an option to improve the
efficiency and avoid excessive oversizing in the conductors, because both weight and energy consumption are
critical in vehicles. In applications with higher consumption, such as data centers that normally use 380-400 V, the
increase of the voltage level is unavoidable because distribution losses need to be minimized. It is at these and
greater voltage levels that more effective protections system need to be developed. When analyzing LVdc distribution systems for building/residential applications, there
are some voltage levels that come as natural choices,

depending on the regulation imposed by the standards,
the availability of commercial solutions, or to ensure compatibility with the ac grid. A summary is shown in Table 1.

TABLe 1. The primary voltage levels for

LVdc distribution for building/residential
applications.
Voltage Level

Advantage

≥565 V

Direct interconnection with the
three-phase, 400-V ac grid

380-400 V

Standard in the data-center
industry

325 V

Minimum modification required for
loads with input rectifier

230 V

Compatibility with pure resistive
loads

120 V

Limit for extra-LV definition, no
need for protection system against
indirect contacts

48 V

Standard in telecommunication
industry

24 V

EMerge Alliance Occupied Space
Standard

12 V

Standard in automotive industry

IEEE Electrific ation Magazine / j une 2 0 1 6

25



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