Hybrid and dual mode railway traction - Impact of new technologies

The use of electricity as traction power for rail systems offers many advantages: clean energy with low CO ₂ emissions, high energy efficiency with the possibility of recovering braking energy, the ability to travel at high speeds, and a high freight train load that reduces the number of heavy goods vehicles on the roads. But it requires costly fixed installations, such as substations and catenary wires, which are reserved for high-traffic lines. However, the demand for uninterrupted regional train service (TER), local service to ports and private sidings, where it is technically impossible to install catenary systems for safety reasons, means that on-board traction units must be fitted with energy sources capable of providing sufficient autonomy to carry out their mission.

Urban communities also want to preserve their environment by building new tramway lines, while limiting the installation of overhead contact lines in city centers and reducing the visual impact in the vicinity of historic sites.

Several architectures can be imagined, depending on the target objective: total or partial autonomy, significant reduction in polluting emissions in the case of thermal traction, reduction and smoothing of energy consumption in general. These are dual-mode and hybrid architectures using several energy sources. The continuous improvement in performance and the maturity of certain energy production, conversion and storage technologies, as well as the emergence of new technologies, have made these new architectures possible. Manufacturers and rail operators are seizing this opportunity to design and operate rolling stock.

After outlining some of the basic principles defining dual-mode and hybrid drive systems in the railway sector, we will attempt to assess the suitability of these new "technological bricks" for railway applications, based on their intrinsic characteristics, to meet the objectives set, and in particular their integration on rolling stock.

In the following sections, we'll look at the design of these powertrains, and use a few examples to describe them.

Recent experiments and the operation of these vehicles demonstrate the benefits of these new traction chain architectures. Dual-mode equipment has become commonplace, for example the Nice tramway, AGC self-propelled trains and Régiolis trains. It's also worth noting the desire of rail operators for a "last mile" locomotive, able to cover long distances in electric mode and complete their mission in autonomous mode on port sidings, for example. Traction of long-distance trains at commercial speeds of around 100 km/h requires power of the order of 4 to 6 MW. Transporting the same train to...