IEEE Electrification Magazine - March 2020 - 23

TABLE 1. A comparison of different MG architectures for electric railway systems.

Low

✓

MV DRMG

High

Low

✓

ARMG
AC

Hybrid
ARMG

Substation
I-mplementation

Low

System
Stability

Number
of Neutral
Section
(NS)

Along With Line
Implementation

LV DRMG

Supply Internal
Loads of
S
- ubstation

Power Flow
Capability

Saved in ESSs

MG Type

Fed Back to
the Grid

Supply
Type

Power
Quality
Problem

Supply Adjacent
S
- ection

RBE Utilization

✓

High

No NS

✓

High

No NS

✓

Medium

High

✓

Low

Full

✓

IFC

High

Medium

✓

Medium

Full

✓

RPFC

Low

✓

High

Full

✓

Cophase

Low

✓

High

Half

✓

* It is possible when using reversible substation.
** If the regenerative train is far from the substation, it is not reasonable to supply internal loads due to the high amount of power loss along the line.

positioning. In addition, the problems relating to neutral
sections still persist.

Hybrid ARMG in the Cophase System
So far, all of the presented ARMG architectures are based
on two adjacent single-phase sections with neutral sections between them. These neutral sections can result in
significant problems and make it difficult to transfer
power from one section to another, contradicting the concept of SG. The cophase ERS is introduced to alleviate
these problems. It is comprised of a specially connected
balanced transformer with a back-to-back converter. The
architecture of the hybrid ARMG in the cophase system is
demonstrated in Figure 8. The principles of back-to-back
converters are same as RPFC, but the cophase system can
reduce neutral sections by half the number. All the other
features of cophase-based hybrid ARMG are similar to
RPFC-based hybrid ARMG.

Conclusion
The implementation of the SG concept as the developing
next generation in ERSs can realize impressive capabilities
and opportunities such that in the long run, the architecture of the future ERS looks very different from the current
architecture. In this article, dc and ac RMGs, together with
the concept of the energy hub, are proposed and outlined.
The possible dc RMGs are classified as LVdc- and MVdcbased architectures with distinct features. Meanwhile, the
ac RMGs are categorized into ARMG and hybrid ARMG,
including IFC, RPFC, and cophase structures. The possible
challenges, advantages, and obstacles related to each
structure and integration of DERs, ESSs, and EV-charging
infrastructures are discussed. Table 1 compares the features of different proposed MG architectures for ERSs.
Implementing any of the proposed MG structures to

renew and reconstruct existing railway networks can be
an important step in the evolution of railway sectors
toward SG technologies. However, for the projects and railway networks that are still in the study phase and will be
established in the future, MV DRMG architectures could
be a promising system since they incorporate the advantages of both ARMGs and LV DRMGs.

For Further Reading
A. Verdicchio, P. Ladoux, H. Caron, and C. Courtois, "New
medium-voltage DC railway electrification system," IEEE
Trans. Transport. Electrific., vol. 4, no. 2, pp. 591-604, June 2018.
doi: 10.1109/TTE.2018.2826780.
M. Brenna, F. Foiadelli, and D. Zaninelli, "Electromagnetic
model of high speed railway lines for power quality studies,"
IEEE Trans. Power Syst., vol. 25, no. 3, pp. 1301-1308, Aug. 2010.
doi: 10.1109/TPWRS.2010.2042979.
F. Nejabatkhah, Y. W. Li, and H. Tian, "Power quality control of smart hybrid AC/DC microgrids: An overview," IEEE
Access, vol. 7, pp. 52,295-52,318, Apr. 2019. doi: 10.1109/
ACCESS.2019.2912376.
H. J. Kaleybar, Kojabadi, H. M., Foiadelli, F., Brenna, M., and
Blaabjerg, F. "Model analysis and real-time implementation of
model predictive control for railway power flow controller,"
Int. J. Electr. Power Energy Syst., vol. 109, pp. 290-306, July 2019.
doi: 10.1016/j.ijepes.2019.02.003.
N. Y. Dai, K. W. Lao, M. C. Wong, and C. K. Wong, "Hybrid
power quality conditioner for co-phase power supply system
in electrified railway," IET Power Electron., vol. 5, no. 7, pp. 1084-
1094, Aug. 2012. doi: 10.1049/iet-pel.2011.0292.

Biographies
Morris Brenna (morris.brenna@polimi.it) is with the Polytechnic University of Milan, Italy.
Federica Foiadelli (federica.foiadelli@polimi.it) is with
the Polytechnic University of Milan, Italy.
Hamed Jafari Kaleybar (hamed.jafari@polimi.it) is with
the Polytechnic University of Milan, Italy.

IEEE Elec trific ation Magazine / MARCH 2 0 2 0

IEEE Electrification Magazine - March 2020

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