Energy Efficiency in Train Operation Christian DUBY, Alstom transport (France)

Energy Management Context In recent years, energy prices have soared, which of course have increased costs for railway operators: it is why we need to research new means to save energy. Simultaneously, the energy market has considerably changed: in most developed countries, it is deregulated, giving railway operators an opportunity to define new ways of using energy. Efficient operation of the Railway system is considered as an essential way to energy saving while an efficient management of power level helps to lower the reference subscribed power, giving access to better energy rates. Optimizing such a system on space / time scale as a whole is impossible: problem should be shared in simpler ones.

RailEnergy In 2005, the European Commission has initiated the RailEnergy program to encourage initiatives about energy saving in Railways. While some working groups explore new technologies to decrease energy consumption of future rolling stock and infrastructure, a dedicated working group Energy Efficient Timetabling and Driving explores new ways of using efficiently all existing rolling stock and infrastructure. The working group has conceived a dedicated and comprehensive system for saving power and energy: EETROP (Energy Efficient Train Operation).

EETROP Definition EETROP Domain EETROP aims at optimizing energy costs of any rail transport system, either with AC or DC traction: Intercity Railways, Regional Railways, Suburban Railways, Freight Railroads, Mass Transit, Tramway

EETROP Architecture EETROP comprises 4 cycles operating at different time scales:

Seasonal cycle: energy efficiency applied to Timetable (EETROP Planner) Daily cycle: optimization of daily power (EETROP Manager) Real time cycle:

o Train traffic coordination (EETROP Dispatcher) o Train economical driving (EETROP Driver).

Principles of efficient driving The basic principle of efficient driving is clever use of the time slack, that is the time margin left in each segment of a train journey, with reference to the fastest runtime, in order to dampen any delay during previous segments.

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Two methods are available and can be combined to save traction energy:

Cutting traction and let train coasting when sufficient speed is reached

Limit available power, thus reducing acceleration.

The limitation of power involves the shift to a lower tractive effort / speed curve:

These methods lead to different speed profiles as illustrated hereunder. Adequate combination of methods by a train driving simulator provides energy efficient speed profile. Such simulator and its algorithms are the key components of an EETROP system.

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EETROP benefits EETROP provides substantial benefits to operators:

For all trains where economical driving can be applied, energy saving may reach easily 15 % with a time margin of 5 % only.

Management of power allows a reduction of 15 to 20 % on the reference power used as basis of invoice by power supplier.

EETROP components EETROP Planner EETROP Planner is a tool completing timetabling tools by providing energy efficiency involving one or several criteria or methods. First a timetabling tool is used to produce a timetable meeting commercial objectives (number of passengers per hour or freight tons per day) while respecting safety constraints (occupancy of track circuits and single track sections, etc). Then EETROP planner improves the timetable with respect to energy efficiency while keeping respect of safety constraints and possible commercial constraints.

Objectives EETROP Planner shall be used to save energy in different ways:

Limitation of traction power to smoothen power demand peaks, Improving efficiency of recuperation of regenerative braking, Allowing extensive use of energy efficient driving (EED).

Functions EETROP Planner is an engineering tool supporting timetable design:

The timetable is improved according to selected criteria,

The effects on energy consumption or regenerative braking potential are measured and displayed to engineer;

The robustness of timetable is assessed.

Principle Basic principle starts from effective traction / braking curve vs. distance showing positive peaks (traction) and negative peaks (braking). Adequate positioning of trains on timetable may provide peak compensation:

Power demand is smoothened Regenerative braking is more

efficiently recovered.

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EETROP Manager EETROP manager manages energy at daily level on the complete rail system: train traffic and auxiliaries. Optimizing ways are:

Smoothening of power demand to lower subscribed power and unloading critical zones

Setting economical modes of driving when possible to save energy. The main means are:

The assessment of global power to identify periods of power overload and under-load with reference to subscribed power,

The identification of the peaks of power when they are used as reference for invoicing Functions EETROP Manager is a decision support system: it is not an automatic train operation system; it does not interact directly with train control but provides advices to traffic controller; in that frame, it meets two main functions:

Reporting: inform traffic controller about power demand and energy consumption, with reference to subscribed tariff data,

Optimizing: advise traffic controller about measures able to smoothen power demand and save energy

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Monitoring of power EETROP Manager shall receive electrical measurements from Power SCADA or from dedicated monitoring systems in traction and service substations able to transmit data according to standard protocols (IEC 60870-5 CS 101 or 104, Modbus). Parameters measured are:

Feeding source availability Instant active and reactive power Voltages and currents, Cumulated active and reactive energy

EETROP Dispatcher EETROP Dispatcher operates in real time in coordination with Automatic Train Supervision system (ATS).

Functions EETROP Dispatcher functions are executed in real time with a short time horizon (next hours):

Analyzing online timetable to find out journey time margins (time slacks) Conflict solving (eg single track meeting points) Defining target points (time, place and speed) for each journey segment Communicating target points and power level to on-board EETROP Driver

Interfaces EETROP Dispatcher works with following parameters:

Permanent information: o Track description o Path description o Rolling stock characteristics

From EETROP Manager: o Power limitations on some trains

From ATS: o On-line Timetable o Train priorities o Train position / Signalling events

From EETROP Driver o Train running mode o Optionally, real position of train (e.g. GPS)

EETROP Dispatcher issues following parameters to EETROP Driver:

Speed restrictions Target points for next movements: Future train position specified arrival time as required, at earliest or at latest Power limitations

EETROP Driver A train is like a car: it can be driven cool or nervous with same punctuality results and different energy consumptions. EETROP Driver starts from driving parameters computed by EETROP Manager and assigned by the traffic controller:

Target time of arrival at each next network point Power level to be applied

EETROP Driver uses the train driving simulator, either trackside or on-board, to compute optimized speed profile.

Operation EETROP Driver can be used as:

A Driver Assistance System: system displays speed profile or recommended speed on the Driver HMI in cab

An Automatic Train operation component: after train start and selection of mode by the Driver, the system controls directly traction and braking.

EETROP Driver is coordinated with ETCS when the train is fitted to ERTMS. This is an example of such HMI in cab:

Simulation results In the frame of the Railenergy Energy efficiency working group, many simulations have been undertaken to prove the validity of the concepts of efficient driving. A typical use case is the regional train Milano Voghera in Italy chosen by Trenitalia as a benchmark.

Driving simulation Here are examples of speed profiles using respectively the fastest run (tight mode), the coasting with maximum acceleration (eco mode) and the lo power mode (lp mode with power limited by 80%). Compared with the tight run the eco mode saves 14 % of energy with 5 % of time margin, low power mode provides 15% and a combination of the two provides 16 %.

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Timetabling simulation Timetabling simulation allows detection of worst peaks of power depending on relative position of trains in the timetable. It is a valuable tool for the timetable generator.

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Conclusion The proceedings of RailEnergy Energy Efficiency working group lead to the definition of concepts, methods and system architecture that are of great interest for the designers of railway control systems. Alstom has initiated R & D actions to implement EETROP concepts and architecture in the frame of the REMS system (rail Energy management System).

The Author Christian Duby started career in the software business in 1969 and particularly managed an energy management project at Electricity de France. Then he has been working since 1979 for various Alstom units: oil and gas, hydro and nuclear power generation, Transmission & Distribution . He is system engineer since 2001 in Alstom Transport Information Solutions Division, responsible for Central Control Systems activity design, including Energy Management Systems. He is presently representing Alstom Transport in collaborative projects sponsored by European Commission: InteGRail and RailEnergy.