Energy efficiency on train control: design of metro ATO driving and impact of energy accumulation devices

Reduction in energy consumption has become a global concern, and the EU is committed to reducing its overall emissions to at least 20% below 1990 levels by 2020. In the transport sector measures are focused on planning, infrastructure, modal change, the renewal of vehicles and also programmes for efficient driving. In metro lines equipped with ATO systems, the ATO speed profiles are designed to comply with running times requirements, taking into account comfort and operational restrictions. In the design process, energy consumption can also be considered in order to design the speed profile that minimizes the consumption. A design procedure, based on detailed simulation and on decision theory has been proposed and applied to Metro de Madrid (Madrid Underground). Average energy savings of 13% have been measured. The simulation requires high precision in calculations because the different speed profiles in service differ in a few seconds (around 5s). Given that, all the features of the ATO system, the track, the traction and braking curves and the efficiency of the motor, must be considered. The objective of that design was the minimization of energy consumption without considering the energy of regenerative braking. In metropolitan railways, the regenerated energy is not used if there is no other train starting up at the same time and it is wasted heating resistors. However, the proposed design based on simulation also allows the analysis of different technologies such as on board energy storage devices to improve the use of regenerative energy and its impact on total energy consumption. ATO speed profiles can be redesigned considering the existence of these devices which can take advantage of the regenerated energy increasing the transported mass instead. As a result, the advantages of investing in an on board storage device can be analysed.