IEEE Electrification Magazine - June 2016 - 23

dc Voltage
Standards and Codes
1,500 V: Limit of LVdc,
IEC60038

Applications
1,500 V: Traction
Systems, PV Systems

1,500
1,400
1,300
1,200
1,100
1,000
900

400 V: Limit Telecom dc
Source ETSI EN 300 132-3-1

800
700
600

380 V: Emerge Alliance
(Data/Telecom Std)
120 V: Limit of SELV
and PELV, IEC61140
75 V: Low Limit EU LDV 2006/95EC (Will
Be Replaced by EU LDV 2014/35/EU)
50 V: IEEE 802.3bt, 802.3bu
24 V: Emerge Alliance (Occupied Space Std)

750 V: Trams
Power Systems

400 V: EV

380 V: Data
Center

500
400
300
200
100
0

50 V: Power
Over
Ethernet
48 V: Telecom,
Rural PV Systems,
Trucks

24 V: Lighting
Systems
12 V: Automotive,
Lighting
5 V: Microprocessors,
Electronics

Figure 2. A collection of standards, codes, and applications using LVdc. SELV: separated extra LV; PELV: protected extra LV.

naturally go to zero, CBs must be connected in series to
ensure sufficient arc voltage for clearing; otherwise a redesign of these elements is required for a reliable protection
system. Recently, electromechanical CBs specifically applicable for dc systems with voltages up to 1,500 V have
become commercially available. However, there are other
issues that still must be addressed, such as CB coordination and the fact that upstream power converters either
limit their output current faster than the CBs respond, or
let through fault current to their ac feeds, thus causing
wider system-voltage outages during fault scenarios.

Architectures
It has been shown that LVdc distribution systems are
applied in a large variety of applications, consequently,
different solutions and architectures have been proposed.
Regardless of the power rating or voltage of the system,
the system structure can be generally classified in three
main categories, as follows.
xx
Single bus is the simplest topology, as only two wires
are used to supply the voltages at the point of load.
Also, the power-electronic converters themselves can
be relied upon for fault protection. The automotive and
telecommunication industries have widely used this

configuration at 12 V and 48 V, respectively. Proposed
single-bus distribution systems often differ, depending
on whether the bus voltage is tightly regulated by a
power-control unit, as shown in Figure 3, or a whether
a battery pack is directly connected to the dc bus. For
the latter option, the bus voltage depends on the state
of charge (SOC) and the current of the battery; as a
consequence, this configuration is used in a reduced
number of applications because the battery SOC needs
to be coordinated by all the power-converter units connected to the bus. A modified single-bus topology, in
which the distribution is made by a three-wire (i.e.,
positive pole, neutral, negative pole) bipolar configuration, brings significant advantages for LVdc distribution in building/residential applications. This topology
allows a reduction in the distribution voltage with
respect to the ground, thereby improving safety and
offering three different voltages levels (+VDC, -VDC,
and 2 VDC). Thus, the loads with different power ratings can be connected to the voltage that better suits
them. This topology is depicted in Figures 4 and 5.
xx
Multibus configurations are used when redundant distribution buses are needed to enhance the reliability and
availability of the system, as well as for interconnection
IEEE Electrific ation Magazine / j une 2 0 1 6

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