Novel Control Method for Improving Energy Efficiency of DC Electric Railways

In DC electric railways, trains dissipate excess regenerative braking energy in braking resistors. This energy cannot be recovered and increases the temperature inside the underground tunnels requiring further energy for cooling. Consequently, it is beneficial to use energy storage systems (ESSs) to capture the regenerative energy and release it back to the trains when needed. ESSs have been shown in literature to enable energy saving, reduce peak demand, and minimise voltage peaks and troughs. This paper focuses on the high power and high energy requirements of the ESS that exceed the capabilities (within physical and cost constraints) of the state of the art storage technologies such as batteries. In this study it is discussed how batteries can be combined with supercapacitors to create a Hybrid ESS (HESS) that has high energy and high power capability. The limitations of using such a system in this application are discussed and a novel control method is proposed to maximise potential gains. This novel control method is implemented as an electrical model of a DC electric railway that is designed using Matlab. The simulation results indicate that the proposed control methodology can increase the energy efficiency of the DC electric railway while minimising the ESS size, cost, and degradation.