This paper presents an analysis on using an on-board energy storage device (ESD) for enhancing braking energy re-use in electrified railway transportation. A simulation model was developed in the programming language C++ to help with the sizing of the ESD. The simulation model based on the mathematical description has been proposed for a train equipped with on-board ESD for analysis of effectiveness of its application. A case study was carried out for a metro line taking into consideration train characteristics, track alignment, line velocity limits and a running time table. This case study was used to assess the energy savings and perform a cost-benefit analysis for different sizes of the on-board ESD by applying the proposed approach. It was shown that when additional environmental benefits (reduction of CO2 emissions) are considered, this may significantly improve effectiveness of the investments due to CO2 European Emission allowances.

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Abstract. Electric traction vehicles cooperating with a 3kV DC traction system and equipped with drive systems based on voltage source inverters are the most significant sources of disturbances for a railway signalling system. Every traction vehicle to be authorised for operation on railway lines must fulfil the limits imposed on current harmonics magnitudes and those provided by railway operators. The solution introduced for prototypes of most modern traction drives is to replace the two-level inverters with three-level topology. Therefore, it is essential to establish the influence of the new solution on the railway signalling system. This paper presents a comparative analysis between simulation results delivered for two and three-level traction drive system regarding generation of disturbing current harmonics. Two types of VSI modulation techniques were taken under consideration: sinusoidal PWM (SPWM) and a new one, proposed by the authors, based on selective harmonic elimination (SHE). Furthermore, the authors presented application of one of the SHE based optimization techniques for shaping the EMU's (electric multiple unit) DC side input current harmonics spectrum in order to meet the required limits. The described technique is based on off-line generation of a set of solutions for each of the VSI operating points and selection of the best solution for the assumed criteria. The applied simulation models and the concept of SHE control were verified in a laboratory by means of a low-power drive stand. Using the three-level inverter in traction drives system results in less current harmonics than using two-level topology without modification of the modulation technique. Thus, it does not guarantee fulfilling all limits assumed in this paper. The proposed modulation technique allows for fulfilling the limits, and the technical implementation of the proposed technique in a traction drive system will be considered in future studies. fore, it generates less current and torque harmonics, resulting in lesser power losses and increased life-time of the drive. Another problem is developing a control strategy to make this type of inverters suitable for operation in traction and industrial environment. The application of a direct torque control (DTC) strategy for this purpose was presented in [6].The preferred topology of the three-level inverter for traction application seems to be the neutral point clamped NPC topology (Fig. 3b). This solution requires an additional modification of modulation to eliminate the neutral point voltage fluctuations [5,7,8].

Implementing high-speed trains on Polish railway lines requires a new approach to the issue of power and energy supply via a 3 kV DC power system. Due to the control systems used, modern rolling stock equipped with asynchronous drive allows maintaining a set speed, as far as a locomotive’s power and voltage in a catenary allow it. Characteristics of traction vehicles with asynchronous drives enables run at voltage lower than the rated voltage, however, it entails decrease of consumed power (required for locomotives with power above 2 MW) and loss of motion dynamics. Modernisation of a railway power supply system conducted in Poland since the mid-1990s of the 20th century has intensified in the past couple of years (so-called MUZ-I program) due to the purchase of Pendolino trains, and it primarily include the main lines. A number of modernisation investments (lines E65, E20, E30) are implemented with co-financing from the EU funds. Due to the predicted trains’ speed (200 km/h and above), in order to fulfil the requirements specified in TSI, a power supply system on these lines should ensure achieving high parameters, that is supply of trains with current up to 3.2 kA, while the so-called mean useful voltage should not be lower than 2.8 kV. The article presents solutions introduced on Polish railway and aiming at adjusting the power supply used to the TSI requirements. The range of conducted modernisation works allows for conclusion that the process is in fact a re-electrification of railway power supply systems.