# Analysis, Evaluation and Simulation of Railway
## 3 Results and Discussion  
### Acceleration and Power  
In order to study the storage possibilities of the different locomotive vehicles, some simulations have been performed in the railway route from Alcazar de San Juan to Cartagena. In case of the full-electric locomotives (S-253 and S-252), although some simulations have been carried out in the whole itinerary, nowadays it is only possible to drive along the route from Alcazar de San Juan to Chinchilla, as the rest of the railway track from Chinchilla to Cartagena is not electrified.  
Figure 7: Elemental model for a supercapacitor module (Maxwell MOD0500). This model is associated in series and parallel to define the aggregated ESS model linked to traction or hotel loads.  
The simulator tool has been developed by authors in Matlab, based on the equations already described in Section 2 for obtaining the resistance forces and the tractive effort-velocity and acceleration curves. Once the resistance forces (curve, rail vehicles and grade, if this force is against the acceleration of the train) and the traction effort (motor and, in some cases, grade) is computed, it is easy to obtain the position, speed, acceleration, power and energy that determine the train performance in each trip on the route. For the section been considered, resistance force, due to curves is limited (see Figure 1b). Moreover, Talgo coaches have independent wheels which limit these effects respect to conventional (bogies) coaches. A preliminary version of this tool was presented in References [16; 17].  
The power profile of the locomotives is calculated as the product of the propulsive force and the velocity of the train. When the power takes negative values, it means the engine is generating energy. Acceleration could be obtained from Equation (2). Results obtained for the acceleration and power demand for the different locomotives simulated are shown in Figures 8 and 9.  
As can be seen in Figures 8 and 9, the train has negative acceleration throughout the itinerary, normally when it has to stop in a station, or it reduces speed below the limits of each of the sections of the route. This negative acceleration is achieved through braking. Electrical locomotives have regenerative braking (the traction motor works as a generator), but sometimes the generated energy cannot be returned through the catenary, so braking is achieved through the use of electrical resistors. In this case, the simulation software considers the possibility to inject power (if there are other trains on the track section) or the use of pneumatic, blending or resistive bank braking options, i.e., there is some feedback from Electric and Kinematical parts of the model. This is an important issue because electromechanical limitations can have a major impact on the kinematical behavior of the model (e.g., the variation in traction and braking curves, due to voltage values on overhead lines, which affects accelerations and changes timetables). The interest and impacts of this feedback is analyzed in the  
Figure 8: Power and acceleration for locomotives (**a**) diesel (S-334); (**b**) hybrid (S-730).  
Figure 9: Power and acceleration for electric locomotives (**a**) S-253; (**b**) S-252.  
literature [66]. In the case of diesel units, they also have dynamic braking, in which the power supplied by motors are used to feed roof resistors cooled with forced ventilation. In both cases, energy is used in a non-efficient way.  
In order to improve the energy efficiency and make use of the energy generated in the regenerative braking, the idea is to install batteries and/or supercapacitors, recovering and storing the braking energy. The recovered energy can be used for feeding the same train when it is accelerating, reducing the power peak consumption. In addition, in electrified paths, it could feed other locomotives circulating in the same itinerary or give it back to the grid through the catenary (in the case of reversible substations).