The wireless charging technology in the railroad sector


The wireless charging methods are increasingly more common in the automotive and mobile telephony sectors, where many manufacturers bet on devices which do not require wires or plugs to charge the batteries of electrical vehicles and smartphones. This type of chargers, called inductive, transfer the energy from the issuer to the receiver through an electromagnetic field induced in between.

Public transport has been the last one to benefit from this method. The railroad company from Guipuzcoa CAF and the Technological Centre IK4-IKERLAN have developed a wireless charging system of trams which does not require, unlike the conventional methods, any type of direct electrical contact, such as catenaries, wires or plugs, to charge train batteries.

The novel device comprises two coils which are in charge of inducing the electromagnetic field which enables the transfer of energy. The first coil, called primary or issuer, is buried underground, where it remains connected to the electrical network, in areas where the tram makes its stops. The second coil, called secondary or receiver, is installed at the bottom of the train and carries a small converter.

Thus, when the tram reaches the area where the primary coil has been placed, this one generates current and produces an electromagnetic field which induces another current in the secondary coil, transferring the power which charges the train batteries. This energy transfer is safe by nature and does not affect passengers, since it can only be activated when there is a tram on top.

Thanks to this development, we can take advantage of the stops the tram makes along its way to charge the batteries automatically, with no need to perform any action by the driver, such as the moment we wait for a traffic light, while passengers get off at a stop or when parking in the own parking space.

Prototype for tram

The development has been carried out within the framework of the project ICPT (Inductive Coupling Power Transfer), which started in 2014 and has lasted three years. This proposal is framed within the NUSUR initiative which is in turn subsidized by the Etorgai program of the Basque government.

During this time, IK4-IKERLAN has worked on a prototype designed to transfer 50kW of power which, after validating it in its laboratories, it has been installed in a tram CAF model URBOS, on the test track which it has in Zaragoza.

The result is a compact piece of equipment completely automatic of fast installation and easy maintenance. It offers a power of 50kW, and taking into account the technology used, it could reach the 100kW, values much higher than those dealt with in the automotive sector.