Sustainable traction drives

This paper presents an overview of railway traction systems. Railway vehicles are characterised by low rolling resistance, and high inertia, therefore the traction drives must have suitable capabilities to deliver the required vehicle performance. Both AC and DC motors are in common use in the railway sector, but have very different power delivery requirements, and there are a multitude of power conversion stages that are necessary to transfer the power from the network to the wheels of the vehicle in a smooth manner. These power converters have evolved from simple camshaft controlled mechanical switches, through to compact power electronic converters. State-of-the-art systems are able to regenerate high quality power back into both DC and AC power systems. For those routes which are uneconomic to electrify, the use of on board energy storage offers a means to improve energy efficiency, by providing a store for braking energy which can then be released during acceleration. These types of systems are currently in the development phase, but are expected to enter regular passenger service in the future. Energy storage on the wayside is also being implemented to improve the power performance of existing systems, and to improve the overall energy efficiency by improving the receptivity of the line to regenerated power.