IEEE Electrification Magazine - March 2020 - 13

The emergence of
the smart grid
concept as the
developing nextgeneration
electricity network
has revealed
impressive
capabilities and
opportunities for
reducing emissions,
energy consumption,
and customer costs.

The emergence of the smart grid
(SG) concept as the developing nextgeneration electricity network has
revealed impressive capabilities and
opportunities for reducing emissions,
energy consumption, and customer
costs, as well as improving energy efficiency, reliability, and safety. It has provided a great path of evolution toward
more sustainable technologies comprising distributed energy resources
(DERs) and microgrids (MGs).
Given that electric railway systems
(ERSs) are known as one of the largest
and highest-consumption end users in
the utility grid, the implementation of
SG innovations and technologies in
such large systems is considered an
effective and indispensable undertaking. However, despite the increasing
developments and tremendous progress of SG in the utility power network
and other industry sectors, such progress is delayed in ERSs, even though
they have a high potential to be adapted with SG technologies due to dedicated equipment and lines in transmission and distribution parts. Meanwhile, instead of
substantial replacement of railway infrastructure, more
investigation is necessary regarding the most suitable integrating points and methods. The outstanding features and
benefits have motivated railway experts in recent years to
study and attempt different aspects of integrating SG and
MG technologies to dc and ac ERSs.
Studies include incorporating DERs
such as photovoltaic (PV) array and
wind generation, utilizing regenerative braking energy (RBE), together
with railway power flow controller
and energy storage systems (ESSs),
Trains
as well as charging infrastructures
for electric vehicles (EVs).
In this article, dc and ac railway
microgrids (RMGs), together with
the concept of the energy hub as
the architecture of future railway
power supply systems, are analyzed and outlined to provide a
useful road map to remove restricAuxiliary and
tions and facilitate the developInternal Loads
ment of SG technologies in the
railway sector.

urban regions with a high population density. The high capacity of utilizing RBE in such systems along with
the internal structural similarities
with integrated DERs has increased
its capability to become a smart dc
MG. Most DERs are based on dc
systems, such as PV and ESSs, or
they have a dc section inside, such as
wind generators, which facilitate the
interconnection. The general concept
of a dc railway MG (DRMG) is shown
in Figure 1. Integrating dc ERSs and
DERs in a common dc link acts as an
energy hub that collects the electricity
production from the generators or the
braking trains and delivers it to the
connected loads as the trains, substation internal loads, charging infrastructures for EVs, or feedback to the
grid by means of the reversible substation. A DRMG can provide a significant amount of energy savings by
optimizing power flow and increasing power quality and efficiency. Based on the current
and developing structures of dc railway systems, two
main categories of DRMGs can be studied depending on
the required voltage and power.

Low-Voltage DRMGs
The traditional low-voltage dc railway systems (600-
1,500 V), are commonly used in urban rails, trams, light rail,

Public
Grid
Charging
Infrastructure for
Electric Vehicles

dc Hub

ESSs

Renewable Energy
Sources

DC Railway Microgrid
DC ERSs, known as low-powerdemand systems, are mostly concentrated in metropolitan and

Figure 1. The general concept of DRMG.

	

IEEE Elec trific ation Magazine / MARCH 2 0 2 0

13



IEEE Electrification Magazine - March 2020

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2020

Contents
IEEE Electrification Magazine - March 2020 - Cover1
IEEE Electrification Magazine - March 2020 - Cover2
IEEE Electrification Magazine - March 2020 - Contents
IEEE Electrification Magazine - March 2020 - 2
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