Hybrid trains for the Highlands? Computer Simulations of Fuel-cell/Battery-electric Trains on Secondary Routes in Scotland

Murray-Smith, D. J. and Fisher, P. (2021) Hybrid trains for the Highlands? Computer Simulations of Fuel-cell/Battery-electric Trains on Secondary Routes in Scotland. Technical Report. University of Glasgow, Glasgow. (Unpublished)

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Although electrification is the preferred choice in the decarbonisation of railways in the United Kingdom there are important secondary routes where the business case for electrification is not strong. Examples include the lines north and west of Inverness and the West Highland lines linking central Scotland to Oban, Fort William and Mallaig. These routes all involve relatively long journeys, with few intermediate stations, prolonged gradients and many speed restrictions. Hydrogen fuel-cell/battery-electric hybrid units offer a possible solution for de-carbonisation of passenger services on lines such as these and, early in 2020, Transport Scotland and Scottish Enterprise announced financial support for development of a hydrogen fuel-cell/battery-electric multiple unit for trials in Scotland. The Hydrogen Accelerator group at St Andrews University is involved in management of the project and a contract for converting a former ScotRail Class 314 three-coach electric multiple unit to a hybrid configuration has been awarded to a group of companies led by Arcola Energy Ltd. This project forms part of a more broadly-based move to strengthen relevant industrial and business supply chains within the rail transport sector in Scotland and help promote new industrial/academic collaborations. Hydrogen fuel-cell stacks are characterised by a sluggish response to demanded power-level changes and their efficiency depends on the operating condition. Powertrain control strategies may therefore involve fuel-cell stack operation with slow rates of change that capture power demand, with fast dynamic changes and peak loads being supplied by the battery pack. The battery pack recharges through regenerative braking or from available power from the fuel-cell stack. Optimal powertrain component sizes depend on route characteristics, with relatively flat routes and operation at constant speed favouring large fuel-cells, while routes with prolonged and steep gradients or larger accelerations require larger batteries. Specifications for lengthy routes involving steep and prolonged gradients such as those encountered in the Scottish Highlands present significant difficulties. Mathematical models for longitudinal train motion involving second-order nonlinear ordinary differential equations, derived using Newton’s second law, provide a basis for conventional forward simulation of a train. Power or tractive force variables are applied as an input, with acceleration, speed and distance travelled being defined as outputs. In contrast, the analysis of road-vehicle powertrains often involves a reverse procedure which starts from a duty cycle based on a record of speed versus time with static or quasi-static models being used to estimate steady-state power and energy demands, However, although also involving an inverse type of approach, the simulation methods applied in this paper are based on dynamic models which allow transient power requirements to be understood more fully. These methods have been applied to the assessment of hydrogen train designs for some specific routes and also for test routes having profiles that are chosen to be typical of the routes of interest, but with simplified profiles. It is believed that use of these simplified test routes provides useful physical insight regarding the effect of train characteristics on the specifications for fuel cell stacks, battery packs and other powertrain components. Use of inverse modelling techniques has been found to allow straightforward investigation of performance sensitivities, not only in terms of the longitudinal train dynamics but also the powertrain parameters and route characteristics. Trade-off investigations using these inverse simulation models can be used to reduce the weight and volume of powertrain components and the cost of the train. Fuel-cell efficiency can also be considered, as larger cells allow operation over a wider range of conditions. Findings from the test routes considered allow estimation of powertrain ratings and storage requirements for operation of a three-coach hybrid hydrogen fuel-cell/battery electric train on the Glasgow to Fort William line.

Item Type:Research Reports or Papers (Technical Report)
Additional Information:This is a progress report on an industry and University collaboration. An abbreviated version of this report has been published as an article entitled “The Highlands Hybrid” in the launch issue of a journal entitled Electrical and Hybrid Rail Technology, July 2021, pp 48-50.
Keywords:Hydrogen fuel cell, battery, powertrain, train performance, simulation, inverse, Scotland.
Glasgow Author(s) Enlighten ID:Murray-Smith, Professor David
Authors: Murray-Smith, D. J., and Fisher, P.
Subjects:Q Science > QA Mathematics > QA76 Computer software
T Technology > TF Railroad engineering and operation
T Technology > TJ Mechanical engineering and machinery
T Technology > TK Electrical engineering. Electronics Nuclear engineering
College/School:College of Science and Engineering > School of Engineering
Publisher:University of Glasgow
Copyright Holders:Copyright © 2021 The Authors
Publisher Policy:Reproduced with the permission of the Author

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