Application of Energy Storage Systems for Electric Railways Case Study of Addis Ababa Light Rail Transit
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Date
2019-09
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Addis Ababa University
Abstract
Today‘s innovative technologies for Railway Electrification and Rolling Stock enable an
energy-efficient operation of railway vehicles supplied by the overhead contact line. In
case there is no possibility to recover the braking energy, an onboard energy storage unit
allows absorption of this energy for later use. Therefore the energy consumption and the
Greenhouse gases (CO2) emission can be reduced significantly and the operation of such
rail vehicles equipped with onboard EES on tracks without overhead contact lines is
possible. However, the energy storage system‘s capability of powering the train during
normal power supply system failure has been evaluated. East-West line of Addis Ababa
Light Rail has been considered in modelling and simulation. The energy consumption has
been calculated for the whole line for proper sizing of the onboard energy storage.
The analysis of different storage technologies considering their storage capacities charge
and discharge capability has been reviewed and Lithium-ion battery has been modeled
with a capacity of 76.5kWh. For the supercapacitor, it is difficult to be used alone due to a
higher weight to be added on the train since onboard energy storage is preferred in the
design. Thus, the combination of batteries and Supercapacitor modules has been modelled.
The supercapacitor is used for quick exchange of power between the supply and the train
(power efficiency) while Lithium-ion battery is used for energy efficiency. A power
conversion system using bidirectional DC-DC converter for the charge and discharge and
energy management system is used for the realisation of catenary free system.
The simulation results from Matlab Simulink show that to supply the train with the
traction energy of 10.325kWh, the battery state of charge fall down to 99.9% from fully
charged capacity. On the other hand the state of charge of the supercapacitor technology is
92% and recharged to 99%. The ESS supplies 640kW of power for acceleration time in
the simulation. Energy storage technologies are effective solution to recover the
regenerated energy and power the train during an emergency. The energy storage system
is recharged during stops at stations and by the use of available braking energy.
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Keywords
Energy Storage System, Rail Power Supply System, Light Rail Trains