IEEE Electrification Magazine - September 2014 - 53

railways, it is important to underline
Maximum Speed
that RPSs are generally not infinite
Maximum Speed
grids. RPSs are normally designed to be
able to supply electrical power in the
Speed
Speed
worst-case conditions defined in the
requirements, both for normal operation (with all of the elements of the
Time
Time
system working properly) and for
degraded operation (for instance,
assuming the loss of one or two subPower
Power
stations). In the design process, a specific operation is assumed, including
Figure 3. Two examples of different driving strategies for the same trip and duration (single
rolling stock characteristics, train fre- train), leading to different power profiles.
quencies, and driving strategy (typically MTD). Once the electrification is in service, the operation
to address, especially if a representation of the electrificaconditions change as time goes on: the transport demand
tion is included in the optimization model. It should be
tends to grow (following the economy growth) and so do the
noted that the main objective of the STD can be very
electrical requirements. As long as the operation is less
diverse: minimizing the energy consumption, adapting
demanding than planned, the electrification can provide the
the train consumption to the capacity of the infrastructure
power the trains request. But once the limits of the electrifiin a specific area, and reducing the cost of the electricity.
cation start being reached (e.g., some line sections are temIn Figure 6, in addition to minimizing the energy conporally overloaded, the voltage drops become too large in
sumption (case A), which has been taken as the base case,
specific points, etc.), the electrification starts creating bottletwo other types of driving changes are introduced. Case B
necks to the operation at specific peak moments in specific
corresponds to a limitation of the power peak supplied by
locations. When this occurs, it is, of course, possible to
the electrical grid 2, e.g., due to temporary capacity limitaupgrade the electrification by adding some reinforcements
tions. Naturally, depending on their type (current or volt(additional conductors to the catenary, new substations, etc.).
age capacity limitations), the power consumption should
A different approach would be possible by using RESG techbe modulated differently for better results. If these limitanologies: adapting the operation so that the rated limits of
tions were at a TSS level (instead of at an electrical grid
the electrification are not exceeded. This is the goal of several
level), the adjustments would be similar, but covering a
ongoing research projects, which are exploring these control
different area. Finally, case C corresponds to a transfer of
mechanisms and developing different RESG technologies. An
part of the energy consumption from electrical grid 2 to
example is the project MERLIN, a European initiative that is
electrical grids 1 and 3, which could be advantageous, for
expected to deliver the final results by the end of 2015 (see
instance, if the prices of the energy were higher in the
"The MERLIN Project").
electrical grid 2 [price-oriented driving (POD)].
This section describes some of the features that will be
It should be noted that, in general, modifying the power
possible in future RESGs, grouped into three categories:
profile normally implies modifying the speed profiles and,
1) smart train operation, 2) smart operation of the RPS, and
therefore, the arrival times to the RP. Consequently, in addi3) smart interaction with other power systems.
tion to a spatial shifting of the power consumption, a temporal shifting is also performed. When performing POD, this
Smart Train Operation
can be useful as electricity prices often vary, not only with
As discussed in the "Railway Power System Grids" section,
the location of the supply but also with the time.
train driving provides a flexible tool to the RSO to adjust the
In addition to driving the trains, another important aspect
power consumption profiles to the needs of the system. As
of the smart train operation is the management of all of the
the traction energy consumption represents an important
part of the operation cost, railway companies have devoted
Position
much effort to optimize the driving strategies to minimize
RP 4
the energy consumption. This is normally an offline
(Destination)
process where the results are a reduced set of driving stratRP 3
egies, each for a different journey duration.
Train 1
Train 2
Smart train driving (STD), i.e., controlling online the
RP 2
way the trains are driven, is the most direct mechanism
for performing an active management of the demand
RP 1
Time
(AMD), a key feature in most ESGs, in RPSs. Because of the
(Origin)
computational load it involves, optimizing the train drivFigure 4. The traffic mesh for two consecutive identical trains.
ing in a short time is a major challenge the RESG will have
IEEE Elec trific ation Magazine / s ep t em be r 2 0 1 4

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2014