**2. Electric Traction Applications**

The electric traction drives can be applied to diverse means of transport that use the road or rail transport modes. Regarding the road mode, SCs might be applied in:


On the other hand, within the vehicles that move on rails, it is possible to distinguish between:


Whether they are vehicles that move on rails or on the road, they have a common structure: a traction drive and control system. Its power stage is formed by the traction motor, the power electronic converter, a braking chopper or dynamic brake and a high impedance/ high power density power supply. This power supply has the capacity to absorb high power consumption peaks, while the power inverter drives the traction motor, and the braking chopper limits the DC voltage during braking dissipating the excess energy into a resistor. Figure 5 shows a general electric scheme of the traction system for this type of vehicles.

**Figure 5.** Electrical diagram of a traction converter connected to a high energy/high impedance power source.

Regarding the stages in which the route of a vehicle can usually be divided, the followings are distinguished:


As a consequence, the power fluctuations are very high: positive, minimum and finally negative. The problems in the power system derived from this highly irregular power profile are:


A possible solution to the aforementioned problem is the inclusion of a storage system in the vehicle's power train to supply/absorb high power peaks for short periods (acceleration and deceleration section) and to recover braking energy by eliminating or reducing considerably the size of the chopper. When sizing the storage system, it is required to define the maximum power peaks (positive and negative) and the stored energy level. In general, those vehicles use other main power systems and the storage system would usually operate for periods of less than 1 min. Considering the particular characteristics of SCs (high power density and low energy density), they are a highly recommended option for this type of application.
